FLOW CONTROLS
Technical
Help Guide
Thermal Expansion Valves
Solenoid Valves
System Protectors
Regulators
Basic Rules of Good Practice
Troubleshooting Guide
2006
Table of Contents
Thermal Expansion Valves . . . . . . . . . . . . . . 1
Solenoid Valves . . . . . . . . . . . . . . . . . . . . . . 30
System Protectors . . . . . . . . . . . . . . . . . . . . 42
Regulators . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Basic Rules of Good Practice . . . . . . . . . . . 56
Troubleshooting Guide . . . . . . . . . . . . . . . . 59
Thermal Expansion
Valves
1
2006
Thermal Expansion Valves
The Thermal Expansion Valve is a precision device designed to regulate
the rate of refrigerant liquid flow into the evaporator in the exact proportion
to the rate of evaporation of the refrigerant liquid in the evaporator.
This controlled flow prevents the return of refrigerant liquid to the compressor. The TXV controls the
flow of gas by maintaining a pre determinated super
heat.
The amount of refrigerant gas leaving the evaporator can be regulated since the TXV responds to: (1)
the temperature of the refrigerant gas leaving the
evaporator and (2) the pressure in the evaporator.
Three forces which govern the TXV
operations are (1) the power element
and remote bulb pressure (P1), (2) the
evaporator pressure (P2), and the
super-heat spring equivalent pressure
(P3) see Fig. 1
We are concerned with the single
outlet type of TXV and shall discuss it
under two headings: (1) A valve with
an internal equalizer, and (2) the use
of external equalizer feature.
Internal Equalizer
gas leaving the evaporator decreases, the pressure in the
remote bulb and power assembly also decreases and the
combined evaporator and spring pressure cause the valve
pin to move in a closing direction (P1 less than P2+P3).
For example, when the evaporator is operating with
134a at a temperature of 40°F or a pressure of 35 psig
and the refrigerant gas leaving the evaporator at the
remote bulb location is 45°F a condition of 10°F superheat exists. Since the remote bulb and power assembly
are charged with the same refrigerant as that used in the
system R-134a, its pressure (P1) will follow its saturation
pressure-temperature characteristics. With the liquid in
the remote bulb at 45°F, the pressure inside the remote
bulb and power assembly will be 40 psig acting in an
opening direction. Beneath the diaphragm and acting in a
closing direction are the evaporator pressure (P2) of 35
psig and the spring pressure (P3) for a 10°F superheat
setting of 5 psig (35+5=40) making a total of 40 psig. The
valve is balanced, 40 psig above the diaphragm and 40
psig below the diagraph.
Three conditions present themselves in the operation
of this valve: first, the balanced forces; second, an
increase in superheat; third, a decrease in superheat.
The remote bulb and power element make up a closed
system (power assembly), and in the following discussion, it’s assumed that the remote bulb and power
element are charged with the same refrigerant as that in
the system.
The remote bulb and power element pressure (P1),
which corresponds to the saturation pressure of the
refrigerant gas temperature leaving the evaporator, moves
the valve pin in the opening direction.
Opposed to this opening force on the underneath side
of the diaphragm and acting in the closing direction are
two forces: (1) the force exerted by the evaporator
pressure (P2) and (2) that exerted by the superheat
spring (P3). In the first condition, the valve will assume a
stable control position when these three forces are in
balance. (See figure 1A) (that is, when P1 = P2 + P3). In
the next step, the temperature of the refrigerant gas at the
evaporator outlet (remote bulb location) increases above
the saturation temperature corresponding to the evaporator pressure as it becomes superheated. (P1 greater than
P2+P3) and causes the valve pin to move in an opening
direction. Conversely, as the temperature of the refrigerant
Changes in load, increasing the superheat, will cause
the TXV pin to move in an opening direction. Conversely, a
change, decreasing the superheat will cause the TXV pin
to move in a closing direction. (Fig 1)
2
Thermal Expansion Valves
Factory Settings of Valves
The factory superheat setting of TXVs is made with the valve pin just starting
to move away from the seat. The superheat increase necessary to get the
pin ready to move is called static superheat.
Thermal Expansion Valves are so designed that an increase in superheat of
refrigerant gas leaving the evaporator, usually over and beyond of the factory
static superheat setting, is necessary for the valve pin to open to its rated
position.
This additional superheat is known as gradient. For
example, if the factory static is 6°F superheat, the
operating superheat at the rated stroke or pin position (full
load rating of valve) will be 10°F to 14°F superheat (See
fig. 2).
If the operating superheat is raised unnecessarily high,
the evaporator capacity decreases, since more of the
evaporator surface is required to produce the superheat
necessary to operate the TXV.
Manufacturers usually furnish the adjustable type TXV
with a factory static superheat setting of 6°F to 10°F
unless otherwise specified by the customer.
It also is obvious then that a minimum change of superheat to open the valve is of vital importance because it
provides saving in both initial evaporator cost and cost of
operation.
When using non-adjustable TXVs, it’s important that they
order with the correct factory superheat setting. For
manufacture’s production lines it is recommended that an
adjustable TXV be used in a pilot model lab test to
determine the correct factory superheat setting before
ordering the non-adjustable type TXV.
The TXV operation discussed thus far pertains to the
internal equalizer type of valve.
The evaporator pressure at the valve outlet is admitted
internally and allowed to exert its force beneath the
diaphragm.
External Equalizer
psi is present (See fig. 3). The pressure at point “C” is 27
psig or 10 psi lower than at the valve outlet, point “A”,
however, the pressure of 37 psig at point “A” is the
pressure acting on the lower side of the diaphragm in a
closing direction. With the valve spring set at a compression equivalent to 10°F superheat or a pressure of 9.7
psig, the required pressure above the diaphragm to
equalize the forces is (37 + 9.7) or 46.7 psig. This
pressure corresponds to a saturation temperature of 50°F.
It is evident that the refrigerant temperature at point “C”
must be 50°F if the valve is to be in equilibrium. Since the
pressure at this point is only 27 psig and the corresponding saturation temperature is 28°F, a superheat of 50°F
minus 28°F or 22°F is required to open the valve. This
increase in superheat, from 10°F to 22°F makes it
necessary to use more of the evaporator surface to
produce this higher superheated refrigerant gas. Therefore, the amount of evaporator surface available for
absorption of latent heat of vaporization of the refrigerants
is reduced, the evaporator is starved before the required
superheat is reached.
When the pressure drop through the evaporator is of any
consequence, i.e., in general a pressure drop equivalent
to 3°F in the air conditioning range, 2°F in the commercial
temperature range, and 1°F in the low temperature range,
it will hold the TXV in a relatively “restricted” position and
reduce the system capacity, unless a TXV with an
external equalizer is used. The evaporator should be
designed or selected for the operating conditions and the
TXV selected and applied accordingly.
For example, an evaporator is fed by a TXV with an
internal equalizer, where a sizable pressure drops of 10
3
Thermal Expansion Valves
Since the pressure drop across the evaporator, which
causes this high superheat condition, increases with the
load because of friction this “restricting” or “starving” effect
is increased when the demand on the TXV capacity is
greatest.
side of the remote bulb location.
In general and as a rule of thumb, the equalizer line
should be connected to the suction line at the evaporator
outlet. If the external equalizer type of TXV is used, with
the equalizer line connected to the suction line, the true
evaporator outlet pressure is exerted beneath the TXV
diaphragm. The operating pressure on the valve diaphragm is now free from any effect of the pressure drop
through the evaporator, and the TXV will respond to the
superheat of the refrigerant gas leaving the evaporator.
In order to compensate for an excessive pressure drop
through an evaporator, the TXV must be of external
equalizer type, with the equalizer line connected either
into the evaporator at a point beyond greatest pressure
drop into the suction line at a point on the compressor
When in the same conditions of pressure drop exist in a system with a TXV,
which has the external equalizer feature (see fig. 4), the same pressure drop still
exists through the evaporator, however, the pressure under the diaphragm is now
the same as the pressure at the end of the evaporator, point “C”, or 27psig.
The required pressure above the diaphragm for equilibrium is 27 + 9.7 or 36.7
psig. This pressure, 36.7 psig, corresponds to a saturation temperature of 40°F
and the superheat required is now (40°F minus 28°F) 12°F.
The use of an external equalizer has reduced the superheat from 22°F to 12°F1
Thus the capacity of a system, having an evaporator with a sizable pressure
drop, will be increased by the use of a TXV with the external equalizer as
compared to the use of an internally equalized valve.
When the pressure drop through an evaporator is in excess of limits previously defined, or when a refrigerant distributor is used at the evaporator inlet,
the TXV must have the external equalizer feature for best performance.
The diagram used in this Section thus far has shown the single outlet type of
TXV. Although a multi-circuit evaporator in itself may not have an excessive
pressure drop, the device used to obtain liquid distribution will introduce a
pressure drop that will limit the action of the TXV without external equalizer,
because the distributor is installed between the valve outlet and the evaporator inlet (See fig. 5).
1 This change from 10°F to 12°F in the operating superheat is
caused by the change in the pressure-temperature characteristic of R-12 at the lower suction pressure of 27 psig.
4
Thermal Expansion Valves
Location of External Equalizer
If individual suction lines from the separate evaporator outlets to the common suction line are short,
then install the external equalizer lines into the
separate evaporator suction headers, or as described in the preceding paragraph.
As pointed out earlier, the external equalizer line
must be installed beyond the point of greatest
pressure drop. Since it may be difficult to determinate this point, as a general rule it is safest to
connect the equalizer line to the suction line at the
evaporator outlet on the compressor side of the
remote bulb location. (See fig. 4 & 5). When the
external equalizer is connected to a horizontal line,
always make the connection at the top of the line in
order to avoid oil logging in the equalizer line.
When the pressure drop through the evaporator is
known to be within the limits defined on page 2, it is
permissible to install the external equalizer connection at one of the return bend midway through the
evaporator. Such an equalizer location will provide
smoother valve control particularly when the TXV is
used in conjunction with an Evaporator Pressure
Regulator. However, in all case where any type of
control valve is installed in the suction line, the
external equalizer line for the TXV must be connected on the evaporator side of such a control
valve or regulator.
On a multi-evaporator system including two or
more evaporators each fed by a separate TXV, the
external equalizer lines must be located so that
they will be free from the effect of pressure
changes in the evaporators fed by other TXV. At no
time should the equalizer lines must be joined
together in a common line to the main suction line.
Do not under any circumstance cap or plug the external equalizer connection on a TXV, as it will not operate. If the TXV is furnished with an external
equalizer feature, the external equalizer line must be connected.
Superheat
A vapor is said to be superheated whenever its temperature is
higher than the saturation temperature corresponding to its pressure. The amount of the superheat equals the amount of the
temperature increase above the saturation temperature at the
existing pressure. For example, a refrigeration evaporator is
operating with Refrigerant 134a at 35 psig suction pressure (See
fig. 6). The Refrigerant 134a saturation temperature at 35 psig is
40°F. As long as any liquid exist at this pressure, the refrigerant
temperature will remain 40°F as it evaporates or boils off in the
evaporator.
As the refrigerant moves along in the coil, the liquid boils off into a
vapor, causing the amount of liquid present to decrease. All of the
liquids are finally evaporated at point B because it has absorbed
sufficient heat from the surrounding atmosphere to change the
refrigerant liquid to a vapor. The refrigerant gas continues along the
coil and remains at the same pressure (35 psig); however, its
temperature increases due to continued absorption of heat from
the surrounding atmosphere. When the refrigerant gas reaches
the end of the evaporator, (See point “C”) its temperature is 50°F.
This refrigerant gas is now superheated and the amount of superheat is 10°F. (50°F minus 10°F).
5
The degree to which the
refrigerant gas is superheated
depends on (1) the amount of
refrigerant being fed to the
evaporator by TXV and (2) the
heat load to which the evaporator is exposed.
Thermal Expansion Valves
Adjustment of Superheat
superheat, the recommended practice is to install a
calibrated pressure gauge in a gauge connection at
the evaporator outlet. In the absence of a gauge
connection, a tee installed in the TXV external
equalizer line can be used just as effectively.
The function of a TXV is to control the superheat of
the suction gas leaving the evaporator in accordance with the valve setting.
A TXV which is performing this function within
reasonable limits, it can be said to be operating in a
satisfactory manner.
A refrigeration type pocket thermometer with appropriate bulb clamp may be used or more effective is
the use of a service type potentiometer (electric
thermometer) with thermocouples (leads &
probes).
Good superheat control is the criterion of TXV
performance. It is important that this function be
measured as accurately as possible, or in the
absence of accuracy, to be aware of the magnitude
and direction of whatever error is present.
The temperature element from your Temperature
Meter should be taped to the suction line at the
point of remote bulb location and must be insulated
against the ambient. Temperature elements of this
type, as well as thermometers, will give an average
reading of suction line and ambient if not insulated.
Assuming an accurate gauge and Temperature
Meter, this method will provide sufficiently accurate
superheat readings for all practical purpose.
Superheat has been previously defined as the
temperature increase of refrigerant gas above the
saturation temperature at the existing pressure.
Based on this definition, the pressure and temperature increase of the refrigerant suction gas passing
the TXV remote bulb are required for an accurate
determination of superheat. Thus, when measuring
Common Incorrect Methods of Reading Superheat
On installation where a gauge connection is not
available and the valve is internally equalized
there are two alternate methods possible. Both of
these methods are approximation only and their
use is definitely not recommended:
unknown and will vary with the load. For this
reason, the two-temperature method cannot be
relied on for absolute superheat readings.
It should be noted that the error in the two-temperature method is negative and always indicates
a superheat lower than the actual figure.
1. The first of these is the two-temperature
method, which utilizes the difference in temperature between the evaporator inlet and outlet as the
superheat. This method is in error by a temperature equivalent of the pressure drop between the
two points of temperature.
2. The other method commonly used to check
superheats involves taking the temperature at the
evaporator outlet and utilizing the compressor
suction pressure as the evaporator saturation
pressure.
Where the pressure drop between the evaporator
inlet and outlet is 1psi or less, the two-temperature method will yield fairly accurate results.
However, evaporator pressure drop usually is an
The error here is obviously due to the pressure
drop in the suction line between the evaporator
outlet and the compressor suction gauge.
6
Thermal Expansion Valves
On packaged equipment and close-coupled
installations, the pressure drop and resulting
error are usually small. However, on large builtup systems or systems with long runs of suction
lines, considerable discrepancies can result.
trouble call is due to the use of improper methods
of instrumentation rather than any malfunction of
the valve.
One other error that will be present when trouble
shooting in mountain areas (such as Denver,
Colorado or Salt Lake City, Utah), is the low
gauge pressure compared to sea level readings.
Use a Pressure-Temperature chart that has
correct readings such as Emerson Climate
Technology Flow Control’s 5,000 ft. correction
pocket chart.
Since estimates of suction line pressure drop
are usually not accurate enough to give a true
picture of the superheat, this method cannot be
relied on for absolute values. It should be noted
that the error in this instance will always be
positive and the superheat resulting will be
higher than the actual value.
Restating the above, the only method of checking superheat that will yield an absolute value
involves a pressure and temperature reading at
the evaporator outlet.
Other methods employed will yield a fictitious
superheat that can prove misleading when used
to analyze TXV performance.
By realizing the limitations of these approximate
methods and the direction of the error, it is often
possible to determine that the cause of the
Factors Involved in Valve Selection
possible vertical lift. The only exception to this is
where the valve is located considerably below
the receiver and static head built up is more than
enough to offset frictional loses. The liquid line
should be properly sized giving due consideration to its length plus the additional equivalent
length of line due to the use of fitting and hand
valves. When a vertical lift in the liquid line is
necessary, and additional pressure drop, due the
loss in static head, must be included.
Proper TXV size is determined by the BTU/HR or
tons load requirement, the pressure drop across
the valve, and the evaporator temperature. It
should not be assumed that the pressure drop
across the TXV is equal to the difference between discharge and suction pressures at the
compressor. This assumption will lead to incorrect sizing of the valve.
The pressure at the TXV outlet will be higher
than the suction pressure indicated at the compressor, due the frictional losses through the
distribution header, evaporator tubes, suction
lines, fittings, and hand valves.
The pressure drop across the TXV will be the
difference between the discharge and suction
pressures at the compressor less the pressure
drops in the liquid line, through the distributor,
evaporator, and suction line. ASHRAE tables
should be consulted for determining pressure
drops in liquid and suction line.
The pressure at the TXV inlet will be lower than
the discharge pressure indicated at the compressor, due to frictional losses created by
length of liquid line, valves and fittings, and
7
Thermal Expansion Valves
liquid refrigerant to ensure solid liquid entering the
TXV at all time!!
Since the capacity and the performance of the
TXV is based on solid liquid entering the valve,
careful consideration must be given to the total
pressure drop in the liquid line to determine if
there will be sufficient sub cooling of the liquid
refrigerant to prevent the formation of flash gas.
If the sub cooling of the liquid refrigerant from the
condenser is not adequate then a heat exchanger, liquid sub cooler, or some other means
must be used to obtain enough sub cooling of the
Emerson Climate Technologies has prepared
extended capacity tables for use with the above
mentioned conditions in mind. These extended
tables can be found in the catalog section of each
type of Emerson’s TXVs. Therefore, where
possible always select TXV for actual operating
conditions rather than nominal valve capacities.
Application
In general, for best evaporator performance, the TXV should be
applied as close to the evaporator as possible and in such location
as to make it easily accessible for adjustment and servicing. On
pressure drop and centrifugal type distributors, apply the valves as
close to the distributor as possible. (See fig.7)
The “T” Series valves [with the exception of the “W”-(MOP), G(MOP) or GS-(MOP) gas charged types] may be installed in any
location in the system. The gas charged type must always be
installed in such a manner that the power assembly will be
warmer than the remote bulb. The remote bulb tubing must not be
allowed to touch a surface colder than the remote bulb location. If
the power assembly or remote bulb tubing becomes colder than
remote bulb, the vapor charge will condense at the coldest point
and remote bulb will lose control.
Remote Bulb Location
sure that remote bulb of each valve is applied to the
suction line of the evaporator fed by that valve.
Since evaporator performance depends largely
upon good TXV control, and good valve control
depends upon response to temperature change of
the refrigerant gas leaving the evaporator, considerable care must be given to types of remote bulbs
and their locations. In general, the external remote
bulb meets the requirement of most installations. It
should be clamped to the suction line near the
evaporator outlet, and on a horizontal run. If more
than one Thermal Expansion Valve is used on
adjacent evaporators or evaporators section, make
Clean the suction line thoroughly before clamping
the remote bulb in place. When a steel suction line
is used, it is advisable to paint the line with aluminum paint to minimize future corrosion and faulty
remote bulb contact with the line.
On lines under 7/8” OD the remote bulb may be
installed on top of the line. With 7/8” OD and over,
the remote bulb should be installed at the position
of about 4 or 8 o’clock. (See fig. 8 on next page)
8
Thermal Expansion Valves
If it is necessary to protect the
remote bulb from the effect of an
air stream, after it is clamped to
the line, use material that will not
absorb water with evaporator
temperatures above 32°F. Below
32°F cork or similar material
sealed against moisture is
suggested to prevent ice logging
at the remote bulb location.
Remote Bulb Well
is trapped (See fig. 10). If the liquid refrigerant
collects at the point of remote bulb location, the
Thermal Expansion Valve operation will be erratic
and possibility the valve will be thought to be defective.
When it becomes desirable to increase the sensitivity of the remote bulb, it may be necessary to use
a remote bulb well. This is a particularly true for
short coupled installations and installations with
large suction lines (2 1/8” OD or larger). Remote
bulb wells should be used (1) when very low
superheats are desired and (2) where converted
heat from warm room can influence the remote
bulb. (See fig. 9).
Large fluctuations in superheat in the suction gas
are usually the result of trapped liquid at the remote
bulb location. Even on properly designed suction
lines, it’s sometimes necessary to move the remote bulb a few inches either way from the original
location to obtain best valve action
Do not under any circumstances locate either type
of remote bulb in a location where the suction line
On multi circuit evaporators fed by one valve, locate
the remote bulb away from immediate suction
outlet at point where the suction gas from several
parallel circuits has had an opportunity to mix in the
suction header. Be sure to pull up tight on clamps
so that the remote bulb makes good contact with
the suction line. NEVER APPLY HEAT NEAR
REMOTE BULB LOCATION WITHOUT FIRST
REMOVING THE REMOTE BULB!!
9
Thermal Expansion Valves
Hunting
“Hunting” of TXVs can be defined as the alternate overfeeding and starving of the refrigerant flow to the evaporator.
It is recognized by extreme cyclic changes in both, the
superheat or the refrigerant gas leaving the evaporator and
the evaporator or suction pressure.
“Hunting” is a function of the evaporator design, length and
diameter of tubing in each circuit, load per circuit, refrigerant
velocity in each circuit, temperature difference (TD) under
which the evaporator is operated, arrangements of suction
piping and application of the Thermal Expansion Valve
remote bulb. “Hunting” can be minimized or eliminated by
the correct rearrangement of the suction piping, relocation of
the bulb and use of the recommended remote bulb and
power assembly charge for the TXV.
Operation at Reduced Capacity
The conventional TXV is a self-contained direct operated
regulator which does not have any built in anticipating or
compensating factors. As such it is susceptible to
“Hunting” for causes which are peculiar to both valve
design and the design of the system to which it is
applied.
The ideal TXV flow rate would require a valve with perfect
dynamic balance, capable of instantaneous response to
any change in the rate of evaporation (anticipation) and
with a means of preventing the valve from over shooting
the control point due to inertia (compensation). With
these features a TXV would be in phase with the system
demand at all times and “Hunting” will not occur.
A conventional TXV does not have built in anticipating or
compensating factor. This means that a time lag will exist
between demand and response, along with the tendency
to over shoot the control point. Thus the conventional TXV
may get out of phase with the system and “Hunt”.
Assume that increase in load occurs, causing the
superheat of suction gas to increase. The time interval
between the instant the remote bulb senses the increase
and causes the valve pin to move into opening direction
allows the superheat of the gas to increase still further.
In response to the rising superheat during the time lags,
the valve has moved further in the opening direction,
overshot the control point and admitted more refrigerant to
the evaporator that can be boiled off by load.
During the time lag between the instant the remote bulb
senses the returning liquid refrigerant and the valve
responds by moving in the closing direction, the valve
continues to over-feed the coil. Thus, when the valve does
move in a closing direction, it will again overshoot the
control point and remain in an overly throttled position
until most of the liquid refrigerant has left the evaporator.
The ensuing time delay before the valve moves in the
opening direction allows superheat of the suction gas to
again rise beyond the control point. This cycle, being selfpropagating, continues to repeats itself.
10
Thermal Expansion Valves
Experience has shown that a Thermal Expansion Valve is
more liable to “Hunt” at low load conditions when the valve
pin is close to the valve seat. This is generally thought to
be due to an unbalance between the forces which operate
that valve.
In addition to the three main forces that operate the
Thermal Expansion Valve the pressure difference across
the valve port acts against the port area, and depending
on valve construction, tends to force the valve either open
or closed.
When operating with the pin close to seat, the following
will occur:
With the valve closed, we have liquid pressure on the inlet
side of the pin and evaporator pressure on the outlet.
When the valve starts to open allowing flow to take place,
the velocity through the valve throat will cause a point of
lower pressure at the throat, increasing the pressure
difference across the pin and seat.
This sudden increase in pressure differential while acting
on the port area will tend to force the valve pin back into
the seat. When the valve again opens, the same type of
action occurs and the pin bounces off the seat with a
rapid frequency. This type of phenomenon is more
frequently encountered with the larger single ported TXVs
as the force due to the pressure differential is magnified
by the larger port area.
We have seen that a TXV may “Hunt” due the lack of
anticipating and compensating features and an unbalance
in the equilibrium forces at lower end of its stroke.
We know from some experience that a TXV, when
intelligently selected and applied, will overcome these
factors and operate with virtual no ”Hunt” over a fairly wide
load range.
Single ported TXVs will generally operate satisfactory to
somewhat below 50% of nominal capacity but it’s again
dependant on evaporator design, refrigerant piping, size
and length of evaporator, and rapid changes in loading.
Nothing will cause a TXV to hunt quicker than unequal
feeding of the parallel circuits by a distributor or unequal
air loading across the evaporator circuits.
Double-Ported Balanced Thermo Valves
We have seen (above) that the flow pattern of the single ported TVX can cause
difficulties at low load conditions. The larger the port area (larger tonnages) the
more prone is the valve to hunt. Certain type of Emerson’s TXVs have been
designed with two ports or “double ported”. The inlet is so designed as to create a
“counter flow” against the double-ported balance ported valves and thus eliminate
any unbalance across the two ports. (See fig. 11)
Flow through the upper port enters the upper radial holes of the cage seat assembly, moves upward and across the upper seat, down through the internal passage
of the spool and out the holes in bottom of the spool.
The pressure drop across this port exerts a force in a closing (upward) direction.
Flow through the bottom port enters the lower radial holes of the cage seat
assembly and moves downward through the port formed by the cage seat and the
valve spool. High-pressure liquid acts downward on the spool and the pressure
drop across the spool and seat exert a force in an opening direction.
Since the effective port area of both the upper and lower cage port is very nearly
the same, the net force unbalance across them is negligible.
This feature makes it possible for the double-ported cage assemblies to modulate
over a much wider load range than was possible with the old style, single port
valves. The reverse-flow valves provide satisfactory control at loads less than 15%
of nominal valve capacity. Their performance is superior to any competitive product
available. Actual field performance has proven the superiority of double-ported
Emerson’s TXVs and their ability to reduce “Hunting” to a very minimum.
11
Thermal Expansion Valves
TXV Charges
Over the years or more precisely, since Emerson
Climate Technologies produced the first valve for
ammonia in 1925, the matter of a proper power
charge in the thermal sensing element has been a
major concern. Liquid charges, gas charges, cross
liquid charges, cross vapor charges, high temperature charges, ultra-low temperature charges,
commercial charges, etc. all have been tried with
varying degrees of success.
An explanation of each type of power element
charge would be in order except for the fact that for
the past several years Emerson has had and still
uses a rather unique power element charge that
covers nearly all types of applications in temperature ranges of –20°F to +50°F. This “C” charge is
available for R-134a, R22, R404, R507 and others.
The “C” Charge
the refrigeration unit pulled down in temperature
resulting in the necessity to make readjustment
at times.
The cross charges (C & Z) usually would create
conditions of high superheat upon start up and
reduce the superheat as the unit pulled down
thus again the need to adjust as the unit got
colder. Between the operating conditions of –
20°F to +50°F the straight C charge rarely if ever
needs to be re-set after a satisfactory superheat
has been established. In fact, the straight C
charge as received from the factory will not have
to be re-set at all in the majority of cases.
Unlike certain past charges; i.e.: G, GA and Q,
the straight C charge (no MOP) will not lose
control in cross-ambient conditions. This is to
say that if the TXV body should get colder than
sensing bulb the gas charge will migrate from
the bulb to the valve head and thus become
inoperative.
The straight C charge absolutely will not “cross
ambient” or lose control as in the above conditions.
The old liquid (L) and gas (G) charges could
create conditions of low superheat upon start up
and would increase the superheat conditions as
M.O.P.
Once below the MOP, the TXV will re-open and feed
in a standard manner or until such time as there is
an overload again.
Maximum Operating Pressure (sometimes
referred to as Motor Overload Protection) is
the ability of a TXV to close down, starve, or
completely shut off if the suction pressure
should approach a dangerously high predetermined limit condition. A condition such as to
cause overheating a suction cooled compressor or loading the crankcase with too dense a
vapor pressure.
The C charge can be supplied with the MOP
feature if needed for system protection. This need
rarely occurs in modern day refrigeration except
such conditions as immediately after defrost or on
gasoline driven compressors such as truck refrigeration.
With the TXV in a closed condition due to MOP the
compressor has a chance to gain on the excess
low side pressure and pull the suction back down to
satisfactory operating conditions.
12
CAUTION: The C charge with MOP will be
effected by extreme cross ambient conditions.
If this condition should exist install an electric
strip heater around the top part of the TXV.
Thermal Expansion Valves
Emerson TXV Catalog
Solder Bodies
For exact valve selection (ie: refrigerant tonnage,
connections, equalizer style, cap tube length,
adjustment and proper application, air conditioning,
commercial, low temperature) refer to Emerson
catalog.
When soldering, remove power assembly, cage
assembly, and all gaskets. Keep heat away from all
valve parts, except body flange. Use a brazing alloy
or low temperature solder. Be careful to retain all
the solder in the connection.
Direction of Flow
For integral (one-piece) body types be sure to use
plenty of wet rags or chill blocks and direct flame
away from valve body.
Be sure the flow of refrigerant is in the direction
indicated by the arrow on the valve body.
Adjusting T-Series Valves
To adjust, remove seal cap on side of valve and
turn adjusting stem. Turning stem to right
decreases flow and raises superheat.
Turning stem to left increases flow and lowers
superheat. Adjust all “T” series 2 turns (1°F) at
a time. Adjust each valve separately and wait
between each adjustment to observe all results. Always tighten any loosened connections
and replace seal cap. It should be noted that
superheat adjustment will change the M.O.P.
point
13
Thermal Expansion Valves
Installation & Service Data
Emerson “T” series TXVs have three component
parts. Power Assembly, Cage Assembly, and Body
Flange. There are no working parts in the body
flange. It is never necessary to break the line
connections to service the valve. Emerson her-
metic integral TXVs are assembled units which
cannot be taken apart in the field; except that the
strainer may be easily removed for inspection and
cleaning by disconnecting the valve from the liquid
line and removing the inlet flare connection.
Servicing
To inspect, clean, or replace parts on all take-apart types
remove the two cap screws, lift off the power assembly, and
remove cage assembly. Be sure gaskets are replaced in
proper places when reassembling valve (See Figure 12).
When assembling External Adjustment valves (TCL,
TJL, TER, TIR or THR) be sure the two lugs on the cage
assembly fit into the grooves provided for them in the power
assembly (See ,Figure 13). Don’t force valve together. Make
the cage fit properly before tightening body flange. See
EMERSON’s “Service Hints” for detailed procedure recommended for “trouble shooting” a refrigeration or air conditioning
system.
Solenoid Liquid Stop Valves
The TXVs, while produced as a tight seating device, cannot be
depended upon for positive shut off since the seating surfaces
are exposed to dirt, moisture, corrosion, and erosion. In addition,
if the remote bulb is installed in a location where during the “off’
cycle it is influenced by a higher ambient temperature than the
evaporator, the valve will open during a portion of the “off” cycle,
and admit liquid to the evaporator. For these reasons the
installation of a Solenoid Liquid Stop Valve ahead of any
TXV is highly recommended.
Filter-Driers for System Protection
To protect the precision working parts of control valves from
dirt and chips which can damage them and render them
inoperative, and to protect the entire system from the damaging affects of moisture, sludge and acids, a filter-drier should
be installed on every system.
The EMERSON “EK” FILTER DRIER provides the finest
possible protection available with superior filtering action and
the removal of moisture, sludges, corrosive acids and waxes.
14
Thermal Expansion Valves
Pressure Switch Setting
On valves with M.O.P.- Pressure Switch must be
set to cut in at a pressure lower than M.O.P. rating
of the TXV.
Factory Superheat Setting
Unless otherwise specified, all valves will be preset
at the factory at a bath temperature which is predetermined by the charge symbol and/or the MOP
rating. The bath temperature at which the valve
superheat has been set is coded alphabetically in
the superheat block on the valve nameplate, as
shown in Fig. 15.
Thus a valve with “10A” stamped in the nameplate
superheat block has been set for 10°F static
superheat with a 32°F bath. In like manner, a valve
stampled “10C” has been set for 10° of static
superheat with a 0°F bath.
When ordering a valve for an exact replacement,
specify the code letter as well as the superheat
setting desired. When ordering for general stock, it
will not be necessary to specify either the superheat or the code letter, since the standard setting
will cover most applications and minor superheat
adjustments may be made in the field.
Fig. 15
REFRIGERANT CODE NAMES
ARI Standard 750-81 recommends the
following color coding of the TXVs:
R-12
R-22
R-502
R-134a
R410A
R404A
Yellow
Green
Orchid
Light Blue
Rose
Orange
15
Bath
Temperature
Code
Letter
+32°F
+10°F
0°F
-10°F
-20°F
A
B
C
D
E
Thermal Expansion Valves
TXVREPLACEMENTCHARGESYMBOLSCROSSREFERENCE
OLD BULB CHARGES VS. NEW REPLACEMENT BULB CHARGE
AIR CONDITIONING
OLD CHARGE
REPLACEMENT
FW
FG55
FW55
FQ55
FGA
FLA
FGS
FWS
FC
FWS
HC
HW
HG100
HW100
HQ100
HGA
HLA
HW85
HGS
HWS
HCA
HC
HW85
HWS
COMMERCIAL REFRIGERATION
OLD CHARGE
REPLACEMENT
REFRIGERANTR12/R134a
F OR FL
FC
FC
FW
FG35
FW35
FW35
FQ35
—
—
FGS35
FGS35
FWS
FWS
REFRIGERANT R22
H OR HL
HC
HW
HG65
HW65
HQ65
HC
HW65
—
—
HGS65
HGS65
HWS
HWS
REFRIGERANTR502/R404A/R507
RL
RC/SC/PC
RW
RW65
RW65
RWS
RWS
LOWTEMPERATURE
OLD CHARGE
REPLACEMENT
—
—
FWZ
—
FW15
FW15
—
FZ
—
FW15/MW15
—
—
FWS
FZ/MZ
FX
FWS
FZ/MZ
FX
—
—
HWZ
—
HW35
HQ35
—
HZ
—
HW35
—
—
HWS
HZ
HX
HWS
HZ
HX
—
—
RWZ
RZ
RW35
RW45/SW45
RWS
RWS
RWS
RZ
RZ/SZ/PZ
NOTE
NOTE: ALL OTHER CHARGE SYMBOLS MUST BE REPLACED WITH AN IDENTICAL MODEL OR AT THE OPTION OF THE ALCO TECHNICAL SERVICE DEPARTMENT WHO MAY MAKE ENGINEERING AUTHORIZED
SUBSTITUTION OF EQUIVALENT TYPE TO PROVIDE EQUIVALENT OPERATION AND PERFORMANCE.
NOTE
NOTE: FOR FIELD REPLACEMENT PURPOSES, HC CAN BE USED TO REPLACE HCA
HCA.
RW
RW110
RWS
RC/SC/PC
16
Thermal Expansion Valves
Servicing Thermal Expansion Valves
The How, The Why, The When!
Thermal Expansion Valves (TXV) are critical parts of a heat pump, refrigeration, or air conditioning system. Proper sizing, installation and adjustment of
a TXV makes the difference in whether the system operates properly or
causes callbacks.
TXV Meters the Flow
Metering the refrigerant flow to the evaporator is the
sole function of a TXV. What’s critical is that it must
meter that flow at the same rate it is being vaporized by the heat load. To do this, it keeps the coil
supplied with the proper amount of refrigerant to
maintain the right superheat of the suction gas
leaving the evaporator.
Superheat: The Measurement
Fig 1. How thermal expansion valve
controls refrigerant flow.
Figure 1 explains how it works. At A, hot, highpressure liquid refrigerant enters the TXV. At B,
cold, low-pressure liquid, plus flash gas, enters the
evaporator. At C, the entire liquid refrigerant has
been boiled off, or vaporized by the heat load (latent
heat). Between C and D, the vapor temperature
increases dramatically as further heat load is
applied (sensible heat). At this point, the gas is
superheated above its saturation temperature. At D,
suction line temperature of the superheated gas is
monitored by the sensing bulb, which signals the
TXV to open or close accordingly.
17
Thermal Expansion Valves
How To Measure Accurately
Because good superheat control is the criterion of TXV performance, accurate measurement is vital.
That involves four steps, shown in Figure 2:
Step A- Determine the suction pressure at the
evaporator outlet with an accurate gage. If there is
no gage connection, a tee installed in the valve’s
external equalizer line can be used.
Step B- Refer to a temperature pressure chart for
the refrigerant used in the system, and determine
the saturation temperature at the observed suction
pressure.
Step C- Measure the temperature of the suction line
at the remote sensing bulb location.
Fig 2. Measuring superheat for proper valve performance
Servicing, Step One
This can be accomplished by a “strap on” thermometer or an electric device similar to an “Annie”
or “Simpson” meter. Be certain the spot chosen for
measurement is clean, to ensure accurate readings.
Step D- Subtract the saturation temperature determined in Step B from the suction gas temperature
measured in Step C. The difference is the operating
superheat.
If the test indicates that a valve adjustment is required, remove the seal cap covering the adjusting stem.
Rotate the stem clockwise to decrease refrigerant flow through the valve and increase superheat; counter
clockwise increases flow and decreases superheat.
When to Use Which Valve
Some servicemen seem rather uncertain as to when to use an internally equalized thermal expansion
valve and when to use an externally equalized one.
Our experience has shown that whenever pressure drop through the evaporator reaches 3psi in a 3-ton
(or 3-hp) air-conditioning system (evaporator temperature range of 30°-50°F), or 2psi in a 2-ton commercial refrigeration system (evaporator temperature of 10°-30°F), or 1psi in a 1-ton low temperature system
(evaporator temperature of zero F or below), an externally equalized valve should be used.
On this basis, an externally equalized valve would automatically be the selection for any system in excess
of 3 tons, regardless of the application.
18
Thermal Expansion Valves
More Rules of Thumb
Always use an externally equalized valve whenever a refrigerant distributor is incorporated in the system.
Good temperature feedback to the TXV is vital for control, so place the bulb where it will provide the best
possible feedback.
Where to Place the Bulb
Fig 3. How to place remote bulb in relation to suction line size
Figure 3 shows the ideal placement
(horizontal) of the bulb in relation to
suction line size. Never put the bulb
at 6 o’clock because it may sense
the temperature of the oil flowing
through the pipe, rather than the
temperature of the refrigerant. And
be sure the bulb location is on a freedraining suction line.
Emerson’s “T” Series: The Simple Answer
Choosing the proper TXV for the specific system remains the first step
in good service and no callbacks.
Emerson’s exclusive “Take-A-Part” series remains the most versatile
TXV on the market and is the only valve you can service in minutes with
one wrench.
And, with its long list of interchangeable power heads, cages and body
flanges, you can mix and match from stock with over 1200 combinations
to fit your job exactly. On anything from heat pumps to commercial units,
1/4 to 100 ton capacities.
Be sure to carry a few Emerson “T” series Take-A-Part thermal expansion valves with you on every call.
See your Emerson Wholesaler for complete specs, and for a look at the
complete line of Emerson precision controls for all your refrigeration and
air conditioning jobs.
19
Emerson’s TXV
Thermal Expansion Valves
Thermal Expansion Valve Charges:
What They Do, and How They Do It.
The basic function of a thermal expansion valve is to control super-heat. But there are several types of
thermal valves, and several types of charges in them. Each has its own specific use; understanding the
power element charge and how it affects the pressure to the power diaphragm is basic to good service.
Types of Charges You’ll Meet
About Liquid Charges
Several basic types of charges are in common
use today. Most common are: liquid charge, gas
charge, liquid cross-charge, gas cross-charge,
and adsorption charge.
Here, the power element contains the same refrigerant as the system in which the valve is used. In
manufacturing, it is put into the remote bulb in a
liquid state. Volume is controlled so that within the
design temperature range of the power element,
some liquid always remains in the bulb.
So power element pressure is always
the saturation pressure corresponding to
the temperature of the remote bulb.
Liquid charges have both advantages
and disadvantages. They include: not
subject to cross-ambient control loss;
little or no superheat at start-up; superheat increases at lower evaporator
temperatures, and slow suction pressure
pull down after start-up.
Liquid Cross Charges
When a liquid cross-charge is used,
the power element contains a liquid
refrigerant different from the system
refrigerant. The pressure temperature
curve of the charge crosses the curve
of the system refrigerant (hence,
cross-charge).
Their advantages include:
• Moderately slow pull down
• Insensitive to cross-ambient conditions
• Dampened response to suction line temperature
changes (minimizes tendency for valve “hunting”)
• Superheat characteristics can be tailored for
special applications
Gas and Gas Cross-Charges
Using a gas charge in place of a liquid alters the
operational characteristics, because gas compresses. At some predetermined temperature, the
gas in the remote bulb becomes superheated,
limiting the force it exerts. This produces higher
superheat at higher evaporator loads and is labeled
the Maximum Operating Pressure (MOP) effect.
Fig 1. Typical cross-charge
pressure/temperature relationship
Note: Emerson charges “C” and “Z” are
liquid cross-charges.
Any MOP point temperature depends on how that bulb was initially charged and where it will be used. All
gas charges are susceptible to cross-ambient control loss when the power element is colder than the
remote bulb. They are inherently faster to respond, but tend to “hunt” for the proper operating level, so a
ballast is often added to the remote bulb to minimize that tendency.
As in liquid charges, the remote bulb can be filled with the same refrigerant as the system refrigerant. Or,
it can be filled with a different refrigerant, producing a gas cross-charge.
20
Thermal Expansion Valves
Adsorption Charges
The final type of charge is adsorption.
In adsorption, solids hold large quantities of gas, not by
taking them into the body of the solid, as in absorption,
but by gathering them and holding them on the surface
of the solid without chemical reaction.
The vapor penetrates into the cracks and furrows of the
solid, allowing considerably greater capacity than
possible with absorption.
Fig 2. What happens with an adsorption charge
The advantage of an adsorption charge is that in a fixed
volume, the quantity of vapor adsorbed varies with the temperature and the system. So it can be used to
exert operating pressure as a function of temperature.
Typical adsorbents include: charcoal, silica gel, activated alumina.
Where to Use Each Type
The chart on the left can help match the
charge to the application
• Adsorption charge “W” – air conditioning, commercial medium temperature
refrigeration, chillers
• Liquid cross-charges “C” and “l”commercial (medium and low temp.)
refrigeration, transport refrigeration, ice
makers
Other types of charges available include:
Liquid charge “L” - icemakers, pilots,
liquid injection valves;
Gas charge “G” - air conditioning (including mobile), water chillers;
Gas cross charge “B” – heat pumps.
Fig 3. Typical operating ranges of today’s most
common TXV charges
If you would like copies of this chart for your wall,
ask your participating Emerson Wholesaler.
Emerson Delivers The Right Charge
Since Emerson invented the modern control valve in 1925, we have carefully developed new charges to
deliver closer control. Specific Emerson Thermal Expansion Valves are available with a variety of charges,
developed in our own laboratory, each designed for long life and close control in specific applications.
Ask Your Emerson Wholesaler
When you plan to replace an expansion valve, check with your Emerson Wholesaler for the quality Thermal Expansion Valve that best fits your application.
21
Thermal Expansion Valves
Troubleshooting Thermal Expansion Valves Part 1:
Causes of Low Suction Pressure
When a thermal expansion valve malfunctions, the cause may not be the valve itself. So many
other components of the refrigeration or air conditioning system may affect it that the key is
proper diagnosis of the problem. We can’t adequately cover the entire subject in one Tech Tips.
So we’ll start with problems resulting in low suction pressure.
A second Tech Tips deals with problems delivering high and fluctuating suction pressure.
Low Suction Pressure With High Superheat
Generally, this is caused by a flow restriction
through the evaporator. If the thermal expansion
valve itself is limiting the flow, look for these probable causes:
1. Inlet pressure might be too low because of excessive
vertical lift; or the liquid line might be too small; or
condensing temperature might be too low. All three result
in inadequate pressure differential.
Solution: Increase head pressure, or replace the
liquid line with the proper size specified by the manufacturer.
2. There may be gas in the liquid line from pressure drop,
an insufficient charge or non condensable gases in the
system. Use a sight glass, or listen for a characteristic
whistling sound at the expansion valve.
Solution: Depending on the cause, either add charge
to the system or purge the non condensable, clean the
strainers and replace the filter-driers, check for proper
line size, or increase head pressure, decrease temperature (provide sufficient sub-cooling) to assure solid liquid
at the valve inlet.
3. The valve might be restricted by the pressure drop
through the evaporator.
Solution: Switch to an Emerson thermal expansion
valve with an external equalizer.
4. The valve orifice might be plugged.
Solution: If ice (moisture) or wax plugs it, there’ll be
a sudden suction line pressure rise after the system is
shut down and warms up or the valve body is artificially
warmed. Moisture and dirt problems are remedied by an
Emerson EK filter-drier. Wax or oil buildup is usually
caused by the wrong type of oil. Replace it with the
proper oil.
5. Superheat adjustment may be set too high.
Solution: Readjust it to the manufacturer’s specifications, following the instructions supplied with the valve.
Fig. 2 Basic forces at work on TXV
6. The valve’s power assembly might have lost charge or
failed.
Solution: Either replace the assembly or the entire
valve.
7. In a cross-ambient condition, a gas-charged power
assembly or the remote bulb tubing may become colder
than the sensing bulb, and the bulb loses control.
Solution:
a) insulate or provide artificial heat to the
power assembly;
b) replace with an Emerson Liquid Cross
Charged Valve.
8. The system’s filter screens might become clogged.
Solution:Clean all filter screens.
22
Thermal Expansion Valves
Something other than the thermal expansion valve
could cause a restriction. If so, you’ll usually find frost
or lower than normal temperatures at the restriction
point. Look for these probable causes:
1. Strainers or filter-driers could be clogged or too
small.
Solution: Replace or clean all the strainers, and
then add an Emerson EK filter-drier to the system.
2. A solenoid valve could be malfunctioning or failed.
Solution: Either way, replace it with the proper
Emerson solenoid valve.
3. The service valve at the liquid receiver, a hand
valve, or the discharge/suction service valve might be
too small or not fully opened.
Solution: Repair or replace the faulty valve if you
determine it can’t be fully opened, and replace any
undersized valves with the correct-sized unit.
Fig 3. Highly efficient Emerson’s EK
Liquid line filter-drier
Protect the System
No matter what the cause, every time
you provide major service to any system,
be sure to protect it (and reduce callbacks) by installing an Emerson EK
liquid line or an Emerson ASD suction
line filter-drier. You’ll be glad you did.
4. Miscellaneous problems could cause trouble, like
plugged lines, too small liquid lines and suction lines.
Solutions are self-explanatory, once you have
determined the cause.
Low Suction Pressure With Low Superheat
Low pressure and low superheat usually mean the
system has poor distribution or inadequate evaporator loading. Look for these probable causes:
1. When distribution is poor in the evaporator,
liquid can short-circuit along favored passes and
throttle the valve before all passes are properly
charged.
Solution: Clamp the power assembly to a free
draining suction line. Clean the line before clamping
the bulb in place. Install a distributor and balance
the evaporator load distribution.
3. The evaporator may be too small, demonstrated
by excessive ice formation.
Solution: Install the proper-sized evaporator.
4. Low air flow resulting from plugged filters or an
inoperative fan motor.
Solution: Clean or replace filter. Check fan motor
speed and repair or replace.
There are additional possibilities but generally you
will find that these are the major problems associated with low suction pressure.
2. The compressor can be oversized, or it can be
running too fast due to a wrong-size pulley.
Solution: Provide compressor capacity control
for oversize; change to the proper-sized pulley.
23
Thermal Expansion Valves
Troubleshooting Thermal Expansion Valves Part 2:
Causes of High Suction Pressure
When troubleshooting a thermal expansion valve malfunction, the key to correcting it is knowing how to diagnose the problem. And the cause might not be the valve itself. So many other
components of the refrigeration or air conditioning system may affect the valve that it is impossible to adequately cover the entire subject in one Tech Tips.
In a previous Tech Tips we covered problems resulting in Low Suction Pressure. This Tech
Tips covers High and Fluctuating Suction Pressure.
High Suction Pressure With High Superheat
High Suction Pressure With Low Superheat
Generally, this is caused by an unbalanced system due
to an oversized evaporator, undersized compressor, and/
or a high load on the evaporator. Either way, the load will
be in excess of design conditions.
Solution: The system must be balanced by increasing compressor size or decreasing evaporator size. Test
system capabilities with proper meters. Your Emerson
Wholesaler can supply a chart listing proper temperature
pressure relationships for all popular refrigerants to help
you.
Several system conditions cause this problem. Look for
these probable causes:
A second cause of high suction pressure and high
superheat can be leaking compressor valves.
Solution: Test compressor and replace valves, or
compressor.
1. The compressor may be undersized.
Solution: Test the system’s capacity and replace
with specified compressor size.
2. The valve superheat setting may be too low.
Solution: Determine the suction pressure with an
accurate gauge. Determine the saturation temperature at
the observed suction pressure. Measure the suction gas
temperature at the remote bulb by taping a thermocouple
to the bulb. Then subtract the saturation temperature from
the remote bulb temperature to determine the superheat
of the gas. Follow the valve manufacturer’s directions to
adjust superheat to the proper setting.
3. There may be gas in the liquid line (from pressure drop
or an insufficient charge) with an oversized TXV.
Solution: Replace the TXV with a proper-sized valve
and then correct the cause of the “flash gas” (see Tech
Tips TT-01285 on Low Suction Pressure Causes).
4. The valve may be held open by foreign material at the
seat with liquid flood-back.
Solution: Clean or replace the damaged parts. Then
install an Emerson EK filter-drier to remove all foreign
material from the system.
5. Either the diaphragm or the bellows in a constant
pressure (automatic) TXV may have ruptured with liquid
flood-back.
Solution: Replace the valve.
6. The valve’s external equalizer line may be plugged, or
capped.
Solution: Clean a plugged equalizer, or repair it. Or,
completely replace the valve with one having a correct
equalizer.
Fig 1. Emerson expansion valve for small
refrigeration systems
7. Moisture in the line may be freezing the valve open.
Solution: Apply hot rags to the valve to melt the ice.
Then install an Emerson EK filter drier to have a moisture24free system.
Thermal Expansion Valves
Causes of Fluctuating Suction Pressure
Fluctuating pressure indicates a variety of possible causes:
1. Superheat adjustment may be incorrect.
Solution: Adjust the superheat following guidelines in #2
under high suction pressure with low superheat, above.
2. The cause could be a trapped suction line.
Solution: Install a “P” trap to allow for free drainage in the
suction line.
3. Liquid refrigerant may flood back because of an improper
distributor, uneven evaporator loading, or improperly
mounted evaporator.
Solution: Replace the faulty distributor; install power
load distribution devices to balance air velocity evenly over
the evaporator coils; finally, check the evaporator mounting
to provide the proper angle.
4. The external equalizer lines may be tapped at a common
source with more than one TXV in the same system.
Solution:Each valve must have its own separate equalizer line going directly to an appropriate location on the
evaporator outlet. See Figure 3 for an example.
Fig 3. Recommended piping of suction
lines to common main
5. Radical pressure differences across the TXV may be
caused by excessive condenser or blower cycling.
Solution: Check coil surfaces, control circuits, thermostat overloads, etc., and repair or replace any defective
parts.
There are additional possibilities, but these are the most common.
Choose the Proper TXV
Every manufacturer offers a variety of
thermal expansion valves to match the
many conditions you will meet in the
field. If you have any questions about
the proper size, consult your Emerson
Representative. He can advise you
and offer detailed information on which
Emerson valve to select for any
application.
Fig 2. Basic refrigeration system schematic
25
Thermal Expansion Valves
How to Select the Right Capacity TXV for the Job
Assume you must install a new thermal expansion valve in a system because the old one
failed and you don’t know the proper capacity valve.
What do you do? Install a too large valve and you’ll get erratic performance or evaporator
flooding. Too small and you get a starving condition which could result in compressor failure
Don’t Trust Labels
Box labels, valve labels, compressor labels all
give you a rating. But it is a nominal rating based
on a specific set of conditions determined by
ARI or ASHRAE, and may be totally different
than your job. Follow them blindly and you may
end up with expensive callbacks.
Extended Capacity Charts
Each valve manufacturer has an extended capacity
chart to help you determine exactly what valve goes
in what application.
To use them, you need to determine four basic facts:
•
•
•
•
Refrigeration system load;
Liquid temperature entering the valve;
Saturated evaporator temperature;
Pressure drop across the valve.
Here’s how to obtain the information you need:
1. Refrigeration system load
Determine the size of the system in BTU’s or Tons
(12,000 BTU /hr. = 1 Ton). Check the system
manufacturer’s literature, if available. If not, find the
compressor rating on its label, but don’t try to
match your valve to that rating, because the
compressor’s rating may vary, depending on the
desired temperature of the cooled space. Average
evaporator temperature for air conditioning is 45°F;
for refrigeration, it’s 15° to 20°F below the temperature of the coldest product stored. The capacity of
the compressor in refrigeration may be considerably less than its nominal rating on the label. It’s
only a guide to the true valve rating.
Fig 1. Emerson TCLE 2HC,
a typical thermal expansion valve.
2. Liquid temperature entering the valve
With a strap-on thermometer, determine the temperature of the liquid entering the valve. Nominal
valve capacities are established 100°F, vapor-free
liquid entering the valve. If liquid temperature entering the valve is higher or lower, correction factors
on the extended capacity chart will help you compensate.
3. Evaporator temperature
If unknown, estimate the temperature of the evaporator, following the guidelines under (1.) above. It
must be lower than the temperature required in the
cooled space, or no heat transfer will take place.
4. Pressure drop across the valve
Determine the difference between the pressure on
the inlet side versus that on the outlet side of the
valve, not the difference between the head pressure
and the suction pressure, a common mistake. It
may be necessary to estimate taking into consideration pressure drop in fittings, valves, driers, distributors, etc.
26
Thermal Expansion Valves
Here’s An Example
In Figure 2, we selected a nominal 2-ton Emerson TCL (E)
2FC TXV operating at +20°F. evaporator pressure, with a 175lb. Pressure drop - giving a capacity of 3.4 tons. Operating at
liquid temperature of 110°F, the 3.4-ton capacity becomes 3.2
tons when multiplied by the .94 correction factor. In this case,
a nominally-rated 2-ton valve has plenty of capacity for a 3-ton
system. In the same situation, a nominally-rated 3-ton valve
would actually be too big, delivering 4.7 tons and possibly
flooding the evaporator.
So, when you don’t know the exact
valve size, take a few minutes to follow
this scenario and you may save yourself some expensive call backs.
If you would like an Extended Capacity
Chart to help you in your work, ask your
participating Emerson Wholesaler.
Fig 2. Typical Extended Capacity Chart TCL(E) 2FC shown in the shaded bar
Valve Capacities are based on 100°F vapor free liquid refrigerant
entering the valve. To determine the capacities for other temperatures
of vapor free liquid refrigerant entering the valve, multiply the capacity
listed in the above chart by the correction factor listed here.
Liquid Temperature Correction Factors
Refrigerant
Type
R-12
R134a
R-22
R404A
Refrigerant Liquid Temperature (°F)
0
1.60
1.70
1.56
2.00
10
1.54
1.63
1.51
1.90
20
1.48
1.56
1.45
1.80
30
1.42
1.49
1.40
1.70
40
1.36
1.42
1.34
1.60
50
1.30
1.36
1.29
1.50
60
1.24
1.29
1.23
1.40
70
1.18
1.21
1.17
1.30
80
1.12
1.14
1.12
1.20
90
1.06
1.07
1.06
1.10
Fig. 3 Typical correction factor chart
27
100
1.00
1.00
1.00
1.00
110 120 130 140
.94 .88 .82 .75
.93 .85 .78 .71
.94 .88 .82 .76
.90 .80 .70 .50
Thermal Expansion Valves
Balanced Port Valves: Old Solution to New Problems
Back in the days when energy was cheap, refrigeration engineers would routinely overspec their systems. Often, condensing temperatures would run as high as 100°, using
much more energy, but they allowed plenty of “slop” to compensate for a wide range of
varying ambient conditions. And everyone was satisfied with the results.
But times change.
Many of today’s systems use base condensing temperatures in the range of 60° to 70°.
They’re more efficient; they provide greater capacity; and they last longer.
But they can also unbalance much more readily, changing superheat, capacity and efficiency, maybe even flooding the compressor.
Balanced Port: Balanced System
Cancelled Forces
A useful solution to the unbalance
problem is an idea that has been
around for a long time, 30 years in
fact, balanced port valves (sometimes called “double-port valves”).
The difference in construction of the two
types of valves makes all the difference. In
the balanced port valve, Fig. C, a small
shaft connects the valve pin to the closefitting rod above the line opening. It is equal
in area to the effective port area.
In effect, balanced-port valves
“balance” the system by operating
at a constant superheat over a wide
range of head pressure and load
variations.
How It Works
In a conventional expansion valve,
Fig. B, with the flow direction such
that inlet pressure is applied under
the valve pin, as pressure increases, the valve tends to move in
an opening direction.
Conversely, when inlet pressure
falls, the valve tends to move in a
closing direction. This change in
valve pin position with a change in
inlet pressure is called unbalance. It
results in erratic operation and
variation from the original superheat
setting.
When increased pressure is applied, it
pushes on both the pin and the rod.
Because it is acting on two equal areas in
opposite directions, the pressure change
Fig A: Emerson HF –
cancels out - and the valve remains in its
typical balanced port TXV
original modulating position.
Applications
It would seem, then, that a balanced port
TXV is a system “cure all.” But although it
will allow the system to operate in a
slightly wider range of head pressure and
load conditions, valves must still be
properly selected to ensure proper system
performance.
Fig B: Standard TXV in
unbalanced condition:
pin being forced open
The same phenomenon occurs
when the outlet (evaporator) pressure varies as load conditions vary,
with the same results.
28
Normally, the properly sized standard TXV
will work well in the system for which it
was designed.
When properly sized, it will keep the
system operating at high efficiency, with
good economy.
If your area has a tendency toward rapid
wide swings in temperature (30° or more
in 24 hours), you may want to consider
balanced port TXVs on some of the
“trouble” systems.
Thermal Expansion Valves
Emerson’s HF Line
At that time, see your Emerson Wholesaler about the Emerson
HF line of balanced port valves. He can give you full specs and fit
your needs perfectly with Emerson quality.
HF Series Features
• Capacities 1/8 thru 13 tons for R-404A/R502
• Bar-stock brass body
• Replaceable power assembly
• Internal/external equalizer
• Field-proven internal seal construction
• Tailored bulb charges for specific temperature ranges
• Interchangeable with other commercial refrigeration TXV’s
Fig C. Balanced port TXV, forces balanced
Advantages/Benefits
• HF-series TXV’s improve valve operation and stability
under varying system conditions such as: high and low
head pressures; high and low degrees of sub-cooling;
wide range of pressure drops across the valve; and
varying evaporator loads.
• Wider load range characteristics of HF valves can result
in fewer models required to cover the normal range of
commercial refrigeration requirements.
• Larger H-size removable power element provides
smoother and consistent valve control.
• Replaceable power element offers flexibility in matching
charge requirements with system refrigerant.
29
Solenoid Valves
30
2006
Solenoid Valves
Introduction
In most refrigeration applications, it is necessary to start or stop the flow in a refrigerant
circuit in order to automatically control the flow of fluids in the system. An electrically
operated solenoid valve is usually used for this purpose. Its basic function is the same as a
manually operated shut off valve, but by being solenoid actuated, it can be positioned in
remote locations and may be conveniently controlled by simple electrical switches.
Solenoid valves can be operated by a thermostatic switch, float switches, low pressure
switches, high pressure switches or any other device for making or breaking an electric
circuit, with the thermostatic switch being the most common device used in refrigeration
systems.
What Are Solenoid Valves?
A solenoid valve consists of two distinct but integral acting
parts, a solenoid and a valve.
The solenoid is nothing more than electrical wire wound in a
spiral around the surface of a cylindrical form usually of circular
cross section. When an electric current is sent thru the windings, they act as an electromagnet. The force field that is
created in the center of the solenoid is the driving force for
opening the valve. Inside is a moveable magnetic steel plunger
that is drawn toward the center of the coil when energized.
The valve contains an orifice through which fluid flows when
open. A needle or rod is seated on or in the orifice and is
attached directly to the lower part of the plunger.
When the coil is energized, the plunger is forced toward the
center of the coil, thus lifting the needle valve off of the orifice
and allowing flow. When the coil is de-energized, the weight of
the plunger and in some designs, a spring, causes it to fall and
close off the orifice, thus stopping the flow through the valve.
Figure 1A and 1 B show a simple schematic
of a solenoid valve in operation.
Solenoid Anatomy
31
Solenoid Valves
Principles of Solenoid Operation
Solenoids are either direct acting or pilot operated.
The application determines the need for either of
the above types. The direct acting valve is used on
valves with low capacities and small port sizes.
The pilot operated type is used on the larger valves,
thus eliminating the need for larger coils and plungers.
1. Direct Acting
In the direct acting type valve, as discussed under
Solenoid Valve operation, the plunger is mechanically connected to the needle valve. When the coil
is energized, the plunger pulling the needle off the
orifice is raised into the center of the coil. This type
of valve will operate from zero pressure differential
to its maximum rated pressure differential, regardless of the line pressure.
The direct acting type valve is only used on small
capacity circuits because of the increased coil size
that would be required to counteract the large
pressure differential of large capacities. The required coil would be large, uneconomical, and not
feasible for very large capacity circuits. In order to
overcome this problem on large systems, pilot
operated solenoid valves are used.
2. Pilot Operated Valve
The pilot operated solenoid valves use a combination of the solenoid coil and the line pressure to
operate. In this type valve the plunger is attached to
a needle valve covering a pilot orifice rather than the
main port. The line pressure holds an independent
piston or diaphragm closed against the main port.
See figures 2a and 2b. When the coil is energized,
the plunger is pulled into the center of the coil,
opening the pilot orifice. Once the pilot port is
opened, the line pressure above the diaphragm is
allowed to bleed off to the low side or outlet of the
valve, thus relieving the pressure on the top of the
diaphragm. The inlet pressure then pushes the
diaphragm up and off of the main valve port and
holds it there allowing full flow of the fluid. When the
coil is de-energized, the plunger drops and closes
the pilot orifice. Pressure begins to build up above
the diaphragm by means of a bleed hole in the
piston diaphragm until it, plus the diaphragm’s
weight and spring cause it to close on the main
valve port. This type solenoid valve requires a
minimum pressure difference between inlet and
outlet in order to operate.
Types of Solenoids
So far we have explained how a solenoid valve
operates. Now we will discuss the many types of
valves and their respective applications. The three
main types of valves are the 2-way, 3-way, and 4way valves.
2 Way Valves
The 2-way valve, which is the most common type
of solenoid valve, controls fluid flow in one line. It
has an inlet and an outlet connection. This valve
can be of the direct acting or pilot operated type of
valve depending on the need. When the coil is deenergized, the 2-way
valve is normally closed.
Although normally closed
is the most widely used,
two way valves are
manufactured to be
normally open when the
coil is de-energized. See
Figure 3 for an example
Fig 3
of a 2-way valve.
32
Solenoid Valves
Solenoid Valve Selection
and outlet valve pressures. If a valve has a 500 psi
inlet pressure and a 250 outlet pressure, and a
MOPD rating of 300 psi it will operate, since the
pressure difference (or 500-250) is less than the
300 MOPD rating. If the pressure difference is
larger than the MOPD, the valve will not open.
The selection of a Solenoid Valve for a particular
control application requires the following information:
1. Fluid to be controlled
2. Capacity required
3. Maximum opening pressure differential (MOPD)
4. Electrical characteristics
5. Maximum working pressure required (MWP)
The capacities of Solenoid Valves for normal liquid
or suction gas refrigerant service are given in tons
of refrigeration at some nominal pressure drop and
standard conditions. Manufacturers’ catalogs
provide extended tables to cover nearly all operating
conditions for common refrigerants. Follow the
manufacturer’s sizing recommendations. Do not
select a valve based on line size. Pilot operated
valves require a pressure drop to operate and
selecting an oversize valve will result in the valve
failing to open. Undersized valves result in excessive pressure drops.
The solenoid valve selected must have a MOPD
rating equal to or in excess of the maximum possible differential against which the valve must open.
The MOPD or Maximum Operating Pressure
Differential takes into consideration both the inlet
Consideration of the maximum working pressure
required is also important for proper and safe
operation. A solenoid valve should not be used for
an application when the pressure is higher than the
maximum working pressure. Solenoid valves are
designed for a given type of fluid so that the materials of construction will be compatible with that fluid.
Steel or ferrous metals and aluminum are used in
solenoid valves for ammonia service. Special seat
materials and synthetics may be used for high
temperature or ultra-low temperature service.
Special materials are required for corrosive fluids.
Special attention to the electrical characteristics is
also important. Required voltage and Hertz must be
specified to ensure proper selection. Valves for DC
service often have different internal construction
than valves for AC applications, so it is important to
study the manufacturer’s catalog information
carefully.
Minimum Operating Pressure Differential
33
Solenoid Valves
Installation
Solenoid Valves having a spring loaded plunger or
diaphragm may be installed and operated in any
position, however, the older style conventional
solenoid valve with a plunger, which depends on
gravity to close, must always be installed with the
plunger in an upright vertical position with the pipe
horizontal. An adequate strainer or filter drier should
be installed ahead of each solenoid valve to keep
scale, pipe dope, solder, and other foreign matter
out of the valve.
When installing a solenoid valve, be sure the arrow
on the valve body points in the direction of refrigerant flow.
When brazing solder type connections do not use
too hot a torch and point the flow away from the
valve. Allow the valve body to cool before replacing
the valve’s operating insides to ensure that the seat
material and gaskets are not damaged by the heat.
Wet rags and or chill blocks are recommended
during brazing. They are necessary to keep the
valve body cool so that body warpage on closecoupled valves will not occur. When reassembling,
do not over torque.
Application Overview
Application
Product Family
Liquid Line Service
50RB
100RB
200RB/500RB
Liquid or Suction Line Service
240RA/540RA
Hot Gas By-Pass
50RB
100RB
200RB/500RB
240RA/540RA
Pressure Differential Valve for Hot Gas By-Pass
34
710RA
713RA
Solenoid Valves
Solenoid Valve Service Hints
Symptom
Cause
Effect
Normally Closed Valve 1- Movement of plunger (armature) or
Valve Will Not Open
diaphragm restricted.
a) corroded parts
or
b) foreign material lodged in valve
c) dented or bent enclosing tube
Normally Open Valve
d) warped or distorted body due to:
Valve Will Not Close
1. improper brazing,
2. crushing in vise.
1- Clean affected parts and replace
parts as required. Correct the cause of
corrosion or source of foreign materials
in the system.
2- Improper wiring.
2- Check electrical circuit for loose or
broken connections. Attach voltmeter
and/or ammeter to coil leads and check
voltage, inrush and holding currents
3- Faulty contacts on relays or
thermostats.
3- Check contacts in relays and thermostats. Clean or replace as required.
4- Voltage & frequency rating of
solenoid coil not matched to
electrical supply:
a) low voltage
b) high voltage
c) incorrect frequency.
4- Check voltage & frequency stamped
on coil assembly to make certain it
matches electrical source. If it does not,
obtain new coil assembly with proper
voltage & frequency rating.
a) Locate cause of voltage drop and
correct. Install proper transformer,
wire size as needed. Be sure all
connections are tight and that relays
function properly.
b) Excessively high voltage will cause
coil burnout. Obtain new coil as
sembly with proper voltage rating.
c) Obtain new coil assembly with
proper frequency rating.
5- Oversized Valve
5- Install correct size valve – see solenoid catalog and extended capacity
table.
6- Valve improperly assembled.
6- Assemble parts in proper position
making certain none are missing from
valve assembly
35
Solenoid Valves
Solenoid Valve Service Hints
Symptom
Cause
Effect
Normally Closed Valve 7- Coil Burnout
Valve Will Not Open
a) Supply voltage at coil too low
(below 85% of rated coil voltage).
or
Normally Open Valve
Valve Will Not Close
7- Coil Burnout
a) Locate cause of low voltage and
correct (check transformer, wire
size, and control rating).
b) Supply voltage at valve too high
(more than 10% above coil
voltage rating).
b) Locate cause of high voltage and
correct (install proper transformer
or service).
c) Valve located at high ambient.
c) Ventilate or isolate the area from
high ambient. Remove covering or
insulation from coil housing.
d) Plunger (armature) restricted due d) Clean affected parts and replace
to: corroded parts, foreign
parts as required. Correct cause
material lodged in the valve,
of corrosion or source of foreign
dented or bent enclosing tube or
material in the system.
warped or distorted body due to
improper brazing or crushing in
vise.
e) With valve closed, pressure
difference across valve is too
high, preventing valve from
opening.
f)
e) Reduce pressure differential to
less than 300 psi.
Improper wiring:
f)
Inrush voltage drop causing the
plunger to fail to pull into magnetic
field due to:
• Wiring the valve to the load side
of motor starter.
• Wiring the valve in parallel with
another appliance with high
inrush current draw.
• Poor connections, especially on
low voltage, where connec
tions should be soldered.
Wire size of electrical supply too
small.
8- Electrical supply (voltage &
frequency) not matched to
solenoid coil rating.
36
Correct wiring according to valve
manufacturers instructions.
Solder all low voltage connections.
Use correct wire size.
8- Check coil voltage & frequency
rating to be sure it is rated for the
electrical service supplied. Install a
new coil with the proper voltage &
frequency rating.
Solenoid Valves
Solenoid Valve Service Hints
Symptom
Normally Closed Valve
Valve Will Not Open
or
Normally Open Valve
Valve Will Not Close
Valve Closes,
But Flow Continues
(Seat Leakage)
Cause
Effect
9- Diaphragm or plunger (armature) restricted due to: corroded
parts, foreign material lodged in the
valve, dented or bent enclosing
tube, or warped body due to
improper brazing or crushing in
vise.
9- Clean affected parts and replace
parts as required. Correct the cause
of corrosion or source of foreign
material in the system.
Install a filter-drier upstream of the
solenoid valve
10- Manual opening stem holding
valve in open position.
10- With coil de-energized, turn
manual stem in counterclockwise
direction, until valve closes.
11- Closing spring missing or
inoperative.
11- Re-assemble with spring in proper
position.
12- Electrical feedback keeping coil
energized, or switch contacts not
breaking circuit to solenoid coil.
12- Attach voltmeter at coil leads and
check for feedback or closed circuit.
Correct faulty contacts or wiring.
13- Reverse pressures (outlet
pressure greater than inlet pressure), or valve installed backwards.
13- Install check valve at valve outlet,
or install with flow arrow in proper
direction.
1- Foreign material lodged under
seat.
1- Clean all internal parts and remove
all foreign material.
2- Valve Seat damaged.
2- Replace valve or affected parts.
3- Synthetic seat material chipped.
3- Replace valve or affected parts.
4- Valve improperly applied or
assembled.
4- Replace with proper valve or
assemble correctly.
Special Considerations for Industrial Solenoid Valves on next page
37
Solenoid Valves
Special Considerations for Industrial Solenoid Valves
Symptom
Cause
Effect
High Internal seat leakage
(high temperature steam up to 400°)
Wrong seat elastomer
used (Buna N)
Use valve with Teflon seat
elastomer
External leakage
(high temperature steam up to 400°)
Wrong gasket material
used (Neoprene)
Use Ethylene Propylene gasket
High Internal seat leakage
(high temperature steam up to 250° or
water up to 210°)
Wrong seat elastomer
used (Buna N)
Use valve with Ethylene
Propylene seat elastomer
External leakage
(high temperature steam up to 250° or
water up to 210°)
Wrong gasket material
used (Neoprene)
Use Ethylene Propylene gasket
38
Solenoid Valves
Selecting the Right Solenoid Valve for the Job
Although solenoid valves are one of the most common controls in refrigeration and air conditioning systems, they are the source of an uncommon
amount of service troubles if they are not properly applied.
There are a series of do’s and don’ts that can make your working life a
whole lot easier if followed.
Basics of Solenoids
The solenoid’s main function is to start or stop the
refrigerant flow in the circuit automatically controlling the fluid flow to match requirements. When and
how they act depends on the type of valve, capacity, the fluid charge and the valve’s characteristics.
Simply stated, the solenoid valve consists of two
parts: an electrical solenoid coil and a valve. When
electricity passes through the windings of the
solenoid, magnetism draws the valve plunger into
the middle of the coil opening an orifice in the valve
body and allowing fluid movement.
When the current stops, the plunger returns to its
normal position, closing the orifice.
Emerson 100 RB direct-acting solenoid valve
Valve Type is Important
There are two types of solenoids: direct-acting and
pilot-operated. As a generality, direct-acting solenoids are used on small capacity circuits; pilotoperated on large systems.
For good reasons.
Pilot-Operated Valves
Typical pilot-operated solenoid valve in action.
Note how pilot bypasses main valve seat.
Direct-Acting Valves
In this type valve, the plunger is mechanically
connected to the needle valve and directly raises
the needle from its seat when the coil is energized.
It will operate from zero pressure differential to
maximum rated pressure differential regardless of
line pressure.
These solenoids use a combination of mechanical
action and line pressure to operate. Here, the
plunger is connected to a needle valve covering a
pilot orifice, rather than the main port. Line pressure
holds an independent piston or diaphragm closed
against the main port.
When the needle valve opens, line pressure above
the diaphragm bleeds off to the low side thus
relieving pressure on top of the diaphragm, and inlet
pressure opens the valve.
Unlike the directing, the pilot-operated valve requires a minimum pressure difference between the
inlet and outlet to operate.
39
Solenoid Valves
Where the Problems Begin
What seems simple has certain inherent potential
trouble-makers if you disregard basics.
To select the right valve for the job at hand, the
serviceman must consider all these factors:
Typical pilot-operated solenoid valve in action.
Note how pilot bypasses main valve seat
1. Fluid to be controlled. Each valve is rated by its manufacturer for a specific refrigerant
fluid. Don’t overlook that rating.
When the wrong valve-fluid combination occurs, the valve’s capacity changes. Over-sized
pilot-operated valves refuse to open; undersized valves cause excessive line drops.
In addition, different types of materials are used in valve seats depending on the service.
Special seat materials used for high temperatures may deteriorate rapidly in the wrong
fluid.
2. Capacity vs. MOPD. Some servicemen select for line size rather than system capacity.
For “safety’s sake” they pick the next size larger than needed. With too large or too small a
differential, the valve just won’t work as it should, if it works at all. MOPD takes into consideration both the inlet and outlet valve pressures. If a valve has 500psi inlet and 250psi outlet
pressure, and an MOPD of 300psi, it will operate because the difference (500-250) is less
than the 300 MOPD rating. If it is greater than the MOPD, the valve won’t open.
3. Electrical ratings. Both voltage and Hertz ratings of the coil must match the system
ratings. Yet some servicemen neglect these considerations - as they do the type of current
involved. DC-rated valves frequently have different internal construction than do AC-rated
valves.
4. Maximum working pressures (MWP). A solenoid valve must never be used for an
application when the pressure is higher than the maximum working pressure.
Study the Manufacturer’s Catalog
As a general rule, study the manufacturer’s catalog and its specifications carefully before
selecting the valve for the job.
Emerson provides detailed information to guide you in selecting and installing, all its products. Read it carefully, then make your selection following the above guidelines. You’ll have
a lot less trouble and fewer callbacks.
40
Solenoid Valves
Solenoid Valves for Special Applications
The relatively simple and reliable electromagnet
makes the solenoid valve a basic workhorse in
refrigeration systems. Energizing and de-energizing
its coil, either by manual or automatic control, is the
easiest means yet devised to provide on-off control
of refrigerant flow.
The most basic stripped-down model of solenoid
valve is the normally-closed direct-acting configuration, which is held shut by a spring and opened by
energizing the coil. A variation used in larger systems is the pilot-operated type, which is “powerassisted” by system pressure.
The operation and applications of these basic types
of solenoid valves will be covered at the end of this
section. In this Tech Tips we will discuss other
types of solenoid valves designed to meet more
specialized needs. A general understanding of
these special types will be helpful when you run into
one, or a need for one.
An important caution to bear in mind is that the
applicable selection criteria should be used in every
case to ensure that a given valve is compatible with
the proposed application. If there’s any uncertainty,
it’s a good idea to check with the valve manufacturer.
“Bi-Flow” Two-way Solenoid
With Check Valve
This is a conventional normally-closed solenoid
valve, usually a pilot-operated type that incorporates
an integral check valve. It will provide positive
shutoff in one direction but permit flow in the opposite direction. It will typically be installed in the liquid
line in a heat pump system.
Solenoid Coil (Energized)
Internally Adjustable Solenoids
These may be either normally-closed or normallyopen types, and may be applied as a conventional
two-way solenoid or as an adjustable differential
check valve. In the latter application,
the valve will allow flow in one direction even when
closed, when the pressure differential exceeds the
level for which it is adjusted.
These valves can be used in applications where
there is a need for a solenoid valve and check valve
in parallel, thereby simplifying the piping and reducing the number of joints. And, being adjustable, they
also provide more precise pressure control.
41
System Protectors
42
2006
System Protectors
Protecting Your Profits:
General Guidelines on Selecting Filter-Driers
Filter-driers, sometimes called System Protectors, remove harmful elements from the
circulating refrigerant before they can damage the system. There’s no mystery surrounding
them, but choosing the proper filter-drier for a specific system can be a problem if you do
not fully understand what they are and how they work.
Dirt, Waxes, Acid: Trouble
Every system you deal with, whether new installation or a repair, has contaminants in it the second
you open it. They may be insoluble, such as metal
filings not removed in manufacturing, or airborne
dirt that entered when the system was opened. Or,
they may be soluble, such as waxes, acids, water
and resins that develop through reactions between
air, the refrigerant, or lubricant.
Bead-style filter drier, Emerson’s EK-Plus.
Types of Filter-Driers
Commonly, there are two types of filter-driers; each
type has multitudes of versions, but they operate
essentially the same.
Any of these can cause callbacks from system
failure. However, installing a System Protector, an
all-purpose filter-drier, can dramatically lessen
chances for that trouble.
There are simple basic differences to consider:
type of filter, how it filters, and its true capacity.
Core style - manufactured by mixing desiccants
(which actually remove the soluble contaminants)
with a bonding agent, then baking them to give
them permanent shape and to activate the drying
ingredients. Result: a porous block serving as both
filter and drying agent.
Compacted Bead style - as its name implies, the
active desiccant is in bead or pellet form; no bonding material is used. Rather, compacting comes
from mechanical pressure exerted by a spring.
However, compacted bead-style filter-driers usually
include an additional filter network to trap solid
contaminants from the refrigerant, unlike most
block styles.
The separate and distinctive filter media can take
various forms that permit depth filtration with
significantly greater solid contaminant capacity and
achieve optimum contaminant retention during
start-up and shut- down when turbulent conditions
exist.
Fig 1. Proper placement of filter-drier in the system
Compacted Bead vs. Core - core style filter-driers
offer the maximum volume of desiccant in that both
filtering and drying must be accomplished in the
one mass. But, because the block is porous, it
does not hold all solid contaminants; often particles
are washed through channels within the block when
pressures surge. Increasing the holding power is
possible with a more compacted block. But pressure drops increase inversely.
43
System Protectors
Most manufacturers rate their filters to ARI Standard 710. But even though
two clean filter-driers may be rated the same, there can be a vast difference
in flow as the quantity of solids picked UP increases.
Absorption vs. Adsorption
One factor to consider in selection is abvs. ad-sorption. Absorption means a
material’s ability to take another substance
into its inner molecular structure.
An adsorbed substance doesn’t penetrate
the molecular structure. It simply begins
building up on the surface of the adsorbent. Walls, cracks, crevices are part of
the surface area and are able to hold other
substances, greatly increasing capacity.
Modern desiccants are extremely porous
and as such possess a very large amount
of surface area and internal pore volume
of a size and shape to effectively adsorb
and retain water molecules.
Moisture Capacities
Emerson’s EK: State of the Art
Two adsorbents are in general use today: activated alumina,
and molecular sieve; the latter being the most popular,
offering water capacity 3 to 4 times greater than other
adsorbents.
Moisture capacities of filter-driers are normally given in drops
of water per ARI Standard 710, allowing direct comparison of
different types and brands.
The most advanced filter-drier today is the
Emerson EK. Developed through extensive research in the Emerson Engineering
Laboratories, EK combines a process
controlled filter medium to remove solids
with a powerful desiccant for maximum
moisture adsorption.
SAE or all-copper fittings allow easy
installations.
Be sure to carry a few Emerson’s EK
filter-driers with you on every call.
One Important Guide
Tests have shown that the amount of acid and resin pick-up
of an adsorbing agent is almost proportional to the weight of
the desiccant. Size or granulation makes little difference.
There is presently no industry-approved method for rating
acid removal. So weight of the desiccant provides the
handiest measure.
44
System Protectors
The Case for Filter-Driers in the Suction Line
The function of filter-driers in refrigeration and air conditioning systems to trap moisture and
harmful contaminants is well understood and accepted by everyone involved with installing
and maintaining such systems. But their use in the liquid line still tends to be thought of as
the “standard” application; including them also in the suction line hasn’t yet become
standard practice to the same degree.
A filter-drier in the liquid line essentially protects the
system controls - solenoid valves, expansion
valves, pressure regulators, and the like. The
function of the filter or filter-drier in the suction line
is specifically to protect the compressor against the
ingestion of contaminants.
Emerson ASD suction line filter-drier
Such protection is generally encouraged by compressor manufacturers in any case, but there are
two sets of circumstances that make suction line
filters or filter-driers particularly advisable
Field Built-up Systems
It is practically impossible to avoid contamination when assembling a refrigeration
system in the field. Dirt, moisture, metal
particles, copper oxide from brazing all can
be present in the system despite the greatest care, and all are capable of damaging or
reducing the service life of the compressor.
In the case of large and complex systems,
like a single system serving a number of
food cases throughout a supermarket, it is a
generally accepted practice to install a
cartridge-type filter in the suction line. Then,
because of the virtual certainty of contamination during assembly of the system, the
initial cartridge is removed and replaced
after the first few days of system operation.
When considering the price of a compressor, the cost of protecting it with a suction
line filter is quite insignificant.
Cross-section shows desiccant beads surrounding accordiontype filter element
45
System Protectors
Compressor Burnout
A compressor burnout can be expected to release
a variety of pollutants into the system, including
acids. Standard procedures following any compressor burnout should include replacing the liquid line
filter-drier with an over-size unit, in addition to
installing a new suction line filter-drier. Then all
control components and strainers should be thoroughly cleaned and the system triple evacuated to
at least 50 microns before recharging.
When a severe burnout occurs, characterized by
discoloration of the oil, a strong acid odor, and the
presence of contaminants throughout both the
liquid and suction sides of the system, the system
should be flushed and the oil changed, when
possible.
After operating the system for 48 hours while
monitoring the pressure drop across the suction
line filter-drier, the oil should be checked for acid.
This can be done with an Emerson Acid Alert test
kit, and if acid is still present, both filter-driers
should be replaced again.
A Look Inside
Internally, suction line filter-driers
employ the same types of elements
as liquid line units. One is the core
type, in which the filter-drier element
consists of a rigid, cylindrical, porous
block that may perform both the filter
and drier functions, or be used in
combination with a separate accordion-type filter element.
The core type filter-drier is available
either in a hermetically sealed configuration or in take-apart designs with a
replaceable element.
What to Look for… and Look Out for
The latest advancement is the beadtype unit, in which the desiccant
consists of loose beads compacted
into the shell.
Some manufacturers have been known to add an access
valve to their liquid line filter-driers and declare them suction
line filter-driers. This is not a recommended way to go for
two reasons.
This design offers several advantages
over older types, including lower
pressure drop, more desiccant surface area, and greater capacity.
First, a suction line filter-drier should provide for greater
capacity than a liquid line unit, both for better compressor
protection and for less pressure drop.
Emerson’s ASD filter-driers and
ASF filters are both available in
many sizes, all with copper
fittings to make installation a
snap. With their state of the art
filter and desiccant materials,
they’re the most advanced and
most efficient suction line filters
and filter-driers on the market.
Typical system arrangements show suction line filter-drier
installed ahead of the compressor.
Second, when only one access valve is provided on the
filter-drier itself, it is necessary to use the access valve on
the compressor, if it has one, to measure pressure drop.
By contrast, a state-of-the-art suction line filter-drier, such
as Emerson’s ASD series, will include two access valves
for fast and convenient measurement of the pressure drop
across the filter-drier itself, which normally won’t exceed
three pounds. And they’re oversized by design, so that all
you have to do is match the line size and you’re assured of
adequate capacity, even after a compressor burnout.
46
System Protectors
All About Heat Pump Filter-Driers
A heat pump is essentially nothing more than a refrigeration system that is capable of
flowing in either direction. The key to its operation is a four-way reversing valve that routes
the discharge gas from the compressor.
Depending on whether the system is cooling or heating, the indoor and outdoor coils swap
roles, taking turns serving as the condenser and evaporator.
Since conventional refrigerant control components are designed for unidirectional operation, their use in heat pumps requires installation in pairs, one for each direction, with check
valves routing the flow through or around them. Today, because of the growing use of heat
pumps, components such as thermostatic expansion valves are available in bi-directional
versions, as are filter-driers, the subject of this Tech Tips.
One-Way Flow, Both Ways
Emerson BKF bi-directional pump filter-drier
Removing Contaminants
Just like any other refrigeration system, heat
pump system components should have the
benefit of filter-drier protection to remove
solid and soluble contaminants. This may be
handled several ways.
Inside a bi-directional filter-drier the refrigerant always
flows the same direction regardless of which way the
refrigerant is flowing through the system. The internal flow
in this case is controlled by an inlet flapper valve and an
outlet poppet valve on each side of the desiccant block. As
the liquid enters the filter-drier from either direction, the
inlet flapper valve routes it to the outside of the desiccant
core. After it flows through to the inside of the desiccant
core, it exits through the opposite poppet valve.
First, in systems with one-way expansion
valves and check valves, a one-way filterdrier might be installed in series with a check
valve. This would be a “part-time” arrangement, in that filtration would be provided in
only one direction.
Second, a one-way filter-drier might be
installed with each of the check valves, so
that one provides filtration in each direction.
And finally, the simplest arrangement is to
install a bi-directional filter-drier in the common liquid line. Used in combination with a
bi-directional thermostatic expansion valve
such as Emerson’s HF series, the complexity of multiple expansion valves, check
valves, and filter-driers can be completely
eliminated
Schematic of a basic heat pump system.
47
System Protectors
The purpose of this arrangement
is to prevent contaminants
collected in one direction from
being flushed back out when the
flow reverses.
Bi-directional components allow simplification of system
Simplifying While Servicing
When servicing or repairing heat
pump systems, especially older
units, it’s a good idea to simplify
them whenever appropriate by
replacing unidirectional components and check valves with bidirectional components such as
two-way filter-driers. When a bidirectional thermostatic expansion valve and filter-drier are
installed, one-way expansion
valves, check valves, and filterdriers can all be replaced at once
with copper tubing.
That’s about as trouble-free as
you can get.
Cross section showing BFK internal components
Refrigerant flow either direction passes from outside to
inside of desiccant block
48
Regulators
49
2006
Regulators
Hot Gas Bypass... What, Why & How
The many and varied components of air conditioning systems are normally sized as
necessary to provide adequate cooling capacity under the maximum load conditions that
will be encountered during the system’s operation. Yet these same systems are also
required to perform satisfactorily under substantially lesser loads.
In a system operating under low load conditions, the evaporator if left to its own devices
would continue to get colder and colder until it freezes up. As growing numbers of sealed
office buildings required air conditioning systems to operate at lower ambient temperatures
to remove internally generated heat, it became necessary to develop an efficient means of
preventing evaporator freeze-up.
Enter the Hot Gas Bypass Valve
How it Works
The function of the hot gas bypass valve is to feed
in, preferably ahead of the evaporator, hot gas,
which is bled from just down-stream of the compressor. This gas raises the pressure in the evaporator and hence the boiling point, thus retarding
evaporation and cooling. In effect, it artificially loads
the evaporator, reducing its cooling capacity to
match load demand.
Because the temperature in the evaporator is a
function of the pressure, it can be controlled by a
relatively simple pressure regulator. And that’s
exactly what the hot gas bypass valve is.
Through a pressure tap into the suction line ahead
of the compressor, the hot gas bypass valve
senses the pressure in the low side of the system.
As the temperature in the evaporator drops lower
and lower, the corresponding drop in pressure will
cause the valve to open, admitting by-pass gas into
the low side and boosting the pressure.
Although the bypass gas can be introduced into the
suction line between the evaporator and the compressor, as sometimes dictated by piping considerations, it is not the preferred method be- cause it
might also require the addition of a liquid injector
valve to de-superheat the gas to avoid overheating
the compressor. Besides adding to the complexity
of the system, oil return problems might also deliver
a series of undesirable side effects.
In the system, the hot gas bypass valve is operated
by a pressure diaphragm working in opposition to a
spring. System pressure acting on the diaphragm
holds the valve in the closed position until it falls
below the set point, at which time the spring overpowers the pressure and opens the valve.
Bypass system showing preferred outgoing to evaporator inlet
50
Regulators
Adjusting the Set Point
The suction pressure at which the valve opens is
selectable by increasing or decreasing the load on
the spring by turning an adjusting screw. To set it,
the evaporator must be cooled down by shutting off
the fans, blocking off the airflow, or some other
means, until the suction pressure drops to at least
five pounds below the desired set point. Then, by
allowing the pressure to be increased by the
bypass gas, the spring load can be varied until the
valve closes at precisely the desired set point.
Generally, the pressure is set to maintain an
evaporator temperature just above that at which
frost forms.
A Few Cautions
• In systems that utilize a Venturi type distributor, the bypass gas should be fed into the
system between the outlet of the expansion valve and the inlet to the distributor. In
the case of pressure drop distributors that utilize an orifice, the inlet must be between the orifice and the inlet to the distributor.
• The hot gas bypass line should be insulated to minimize system heat loss.
• In systems with sequential compressor unloading, the valve should be set to begin
opening at two to three pounds below the last stage of unloading, because compressor unloading is considerably more efficient and should be utilized before resorting to
bypassing.
• For oil return considerations. The bypass line must feed in ahead of the evaporator
when the evaporator is physically located below the compressor.
• The hot gas bypass valve should be located as close as practical to the condensing
unit, to minimize condensing ahead of it.
• In systems that operate on a pump down cycle, there must be a solenoid valve or
some other means of shutoff in the bypass line.
51
Regulators
Understanding Suction Line Regulators:
Operation & Application
Suction line regulators are used for a variety of refrigeration control functions. But their main
purpose is to balance the capacity of the refrigeration system to the requirements of the load.
By controlling the operating pressure of the evaporator, or the suction pressure of the compressor, they allow the system to meet the requirements of a wide range of load conditions,
and maintain maximum system efficiency.
You don’t have to install suction line regulators on systems of 5 tons or less (unless the system has a history of trouble), but they pay off nicely on larger refrigeration and commercial
systems.
Two Main Types
Basically, there are two main types of suction line
regulators: Upstream, or Evaporator Pressure
Regulators (EPR), and Downstream Pressure
Regulators.
Because the latter regulate pres- sure at the compressor, they are sometimes called Crankcase
Pressure Regulators (CPR).
You’ll find both types located in the outlet side of the
evaporator, between it and the compressor. In
operation, EPRs keep gas pressure at or above a
pre-set level; CPRs keep suction pressure at or
below a pre-set level.
Fig 2. Typical system using line regulators
Figure 1. Emerson EPRBS,
a typical suction line regulator
How EPRs Work
EPRs are the oldest and best known of these
suction line controls. They are designed to work on
multiple evaporator systems.
Figure 3 shows a typical EPR. Operating pressure
limit is set by adjusting the top-mounted screw,
working against the adjustable spring. Pressure
through the inlet gas passage keeps the diaphragm
up, allowing pressure to flow into the pilot port
chamber.
This maintains the main piston in its open position.
When pressure drops below the minimum, the
diaphragm moves downward, opening the pilot
valve and reducing pressure above the piston. In
turn, the piston moves in a closing direction, restricting gas flow and increasing pressure in the
line. Both the pilot and main valves can assume
intermediate or throttling positions to more evenly
regulate pressure in the lines.
52
Regulators
Crankcase Regulators
Normally open, the CPR (Fig. 4),
closes when compressor pressure
rises above the pre-set maximum,
forcing the valve back onto its seat.
As suction pressure drops, the valve
begins reopening, maintaining the
balance.
How to Apply Them
Normally, it isn’t necessary to use both
types in most systems. In fact, about 90%
of all installations are of EPRs only.
Typical installations of EPRs are in supermarket systems, large chillers, and industrial processes where large amounts of
heat must be absorbed. Smaller (including
residential) systems of less than 5 tons are
usually equipped with compressors designed to operate well within assigned 30°40°F. variations.
One of the advantages of suction line
regulators in modular systems, like those
with many cases found in supermarkets, is
that by adding EPRs you can control the
operating temperatures of the individual
cases in a single loop system.
Fig 3. cutaway of evaporator pressure regulator
(Emerson BEPR).
Where to Apply Them
EPRs are most commonly used on multiple evaporator
systems, located in the branch lines close to the required control source. They are used for indirect temperature control. They also maintain evaporator pressure during defrost, conserving power, expediting the
defrost and reducing flood back.
CPRs are usually only applied if the system is being
continually “over-pressured.” If you suspect that’s the
case, check the amp draw on the compressor while it’s
running. If it’s higher than the plate rating, the system
may be a CPR candidate.
It’s always a good idea to talk it over with
your Emerson Wholesaler, who can answer
questions about sizing and application.
Fig 4. Cutaway of crankcase pressure regulator
(Emerson OPR)
53
Regulators
The What, Why and How of Head Pressure Control
What does a head pressure control do? Why is it needed? How does it work?
Knowing the answers to these questions is
important in many refrigeration applications,
and becoming increasingly important in air
conditioning applications. Understanding the
types of systems and applications calling for
head pressure controls is especially important
to assemblers of such systems, whether
factory assembled or on-site assembled.
Emerson Headmaster 3-way valve.
How Head Pressure Contributes
Methods of Maintaining Head Pressure
To start with the basics, adequate head pressure,
the system pressure imposed by the compressor,
is necessary for optimum performance of most
systems. The function of the pressure is to (1)
maintain liquid sub cooling and prevent liquid line
flash gas, (2) apply enough pressure at the inlet
side of the thermal valve to create the pressure
drop across the valve port needed for proper valve
operation, (3) provide for proper operation of system with hot gas defrost or hot gas bypass, and (4)
supply the pressure necessary for operation of heat
reclaim systems.
When the temperature of the condenser cooling air
is an uncontrolled variable, as it typically is, head
pressure can be boosted at lower ambient temperatures by reducing the exposure of the refrigerant to the cooling air. This, in turn, can be done by
controlling either the flow of air or refrigerant
through the condenser.
Ordinarily, when ambient air temperature flowing
through air-cooled condensers is warm enough,
there is no problem maintaining head pressure. But
as ambient temperature falls, there is a corresponding head pressure drop, calling for some
means of artificially maintaining it.
Applications in which systems are required to
operate at lower outdoor temperatures traditionally
include such obvious examples as refrigeration
systems for food processing and storage. But with
today’s “sealed” office buildings, there is a growing
need for air conditioning systems, too, to operate at
cooler temperatures, removing internally-generated
heat. Computers are a primary source.
Controlling the volume of airflow through the condenser coils can be done by cycling cooling fans on
and off, or by a damper system that proportions
airflow passing through, or through bypassing the
condenser. Controlling the flow of refrigerant
through the condenser is by valving, and, because
this offers some distinct advantages over controlling the air- flow, we will concentrate here on valvetype head pressure controls.
Among its major advantages, a head pressure
control valve is capable of precision in maintaining
optimum pressure, typically within a 5-10 psi range,
while airflow control systems might vary as much
as 50psi. In addition, airflow control systems are
effective only down to a certain temperature, while
the refrigerant valving system continues to maintain
head pressure at much lower ambients. Finally, a
valve system is simpler to install and maintain.
54
Regulators
How it Works
Inside of a typical head pressure control is a valve which, when
closed, routes the refrigerant through the condenser to the
receiver, and when open, allows refrigerant gas to by-pass the
condenser. The valve is operated by a pressure charge in the
head of the valve acting on a diaphragm.
When ambient is warm enough, normal head pressure on the
opposite side of the diaphragm counteracts the pressure
charge, keeping the valve closed and routing the refrigerant
through the condenser. As the ambient temperature falls, the
pressure charge overcomes the resulting lower head pressure,
opening the valve and allowing bypass gas to enter the receiver.
This creates back pressure at the condenser outlet, causing a
buildup of condensed liquid in the condenser, popularly referred
to as “flooding the condenser,” which effectively reduces its
working surface and its cooling capacity.
Custom 3-way valve in single system
Upper: Typical single-valve system,
Lower: Typical Dual-valve system
Single & Dual Valve System
Generally speaking, the need for head
pressure control, as dictated by the
application, is adequately met with a
single valve in systems up to about 15ton capacity. This is because such
systems are usually factory-assembled,
with components sized and pre-set for
the specific system. Larger systems
usually employ two adjustable pressure
regulators, one ahead of and one after
the condenser. These systems are
normally assembled on-site from components procured
independently, thus necessitating a means of adjusting
pressures for system compatibility.
The only other component that requires specific sizing for
compatibility with head pressure controls is the receiver,
which must be large enough to accommodate the normal
operating charge plus the additional charge that would be
necessary to totally flood the condenser.
55
Basic Rules of
Good Practice
56
2006
Basic Rules of Good Practice
Basic Rules of Good Practice
Doing a good job in any line of work almost always involves following some basic “good practice” rules, and servicing refrigeration systems is no exception. Knowing and observing such
basic rules, to the point that it becomes automatic, can prevent a lot of problems by cutting them
off at the pass before they have a chance to happen.
A list of DO’s, procedures that should be followed, and a list of DON’Ts representing pitfalls that
should be avoided are presented here to promote the general adoption of good servicing practices and a better understanding of the WHYs behind them. An occasional quick review may
serve to reinforce awareness and help make their application second nature.
DOs
DO maintain test instruments in good working order and periodically check
them against accurately calibrated instruments.
Good diagnoses can’t be made with faulty inputs.
DO familiarize yourself with the operation of a control before attempting to
make adjustments or repairs.
If you don’t understand how a control is supposed to function, you can’t be sure if it’s
defective or not. When you know what you’re doing, you achieve good results on
purpose; when you don’t know what you’re doing, you achieve good results only by
accident.
DO make it a practice to check suction gas superheat at the compressor.
Too low superheat may result in liquid flood-back, while high superheats cause high
discharge temperatures. Always follow equipment manufacturers’ instructions.
DO replace filter-driers or replaceable cartridges whenever it’s necessary to
open a system for service.
Regardless of how careful you are, it’s virtually impossible to prevent the entry of
moisture and other contaminants while the system is open. Driers or cartridges
cannot be successfully activated in the field for reuse. A new filter drier or cartridge
is cheap insurance for a compressor.
DO use an accurate moisture indicator in the liquid line to watch out for
moisture contamination.
It is the single most common contaminant, and it can lead to a variety of problems
including acid, sludge, and freeze-ups.
DO check expansion valve superheat by using the temperature-pressure
method.
This involves measuring the suction line pressure at the evaporator outlet and then
referring to the appropriate temperature-pressure chart to determine the saturation
temperature. Subtracting this temperature from the suction line temperature measured at the remote bulb gives you the operating superheat, which should be
adjusted to the equipment manufacturer’s specifications.
57
Basic Rules of Good Practice
DON’T be a “parts-changer.”
DON’Ts
Analyze problems based on the symptoms, and determine the specific cause
before making any changes or repairs. Emerson’s Troubleshooting Expansion
Valves, Parts I and II, describe a wide variety of problems that may be encountered, and their probable causes.
DON’T think of a thermal expansion valve as a temperature or pressure
control.
Thinking of it as a superheat control is basic to achieving optimum system
performance.
DON’T attempt to use any control for any application other than the one it
was designed for.
Using a pressure regulator for a pressure relief valve-or any similar substitution - is
not good practice and almost certainly won’t deliver proper performance. Misapplications can lead to equipment damage and even injury. When doubt exists, check
with the manufacturer.
DON’T energize a solenoid coil while it is removed from the valve.
Without the magnetic effect of the solenoid core, the coil will burn out in a matter
of minutes.
DON’T install a previously used filter-drier or replaceable cartridge.
It could introduce contaminants that it has picked up since its removal from a
system
DON’T select solenoid valves by line size or port size, but by valve capacity.
They must also be compatible with the intended application with regard to the
specific refrigerant used, the maximum opening pressure differential (MOPD), the
maximum working pressure (MWP), and the electrical characteristics. Never apply
a valve outside of its design limits or for uses not specifically catalogued.
DON’T rely on sight or touch for temperature measurements.
Use an accurate thermometer. Once again, you can’t get accurate diagnoses with
faulty inputs.
One last tip:
DO read the instructions first.
DON’T wait until all else fails!
58
Troubleshooting
Guide
59
2006
TROUBLESHOOTING EXPANSION VALVES
Superheat Is Too Low -- TXV Feeds Too Much
Problem
Symptoms
1) Liquid Slugging
Valve Feeds
2) Low Superheat
Too Much
3) Suction Pressure Normal or High
Causes
Corrective Action
Oversized Valve
Replace with correct size valve
Incorrect Superheat Setting
Adjust the superheat to correct setting
Moisture
Replace the filter-driers; evacuate the system
and replace the refrigerant
Dirt or Foreign Material
Clean out the material or replace the valve
Incorrect Change Selection
Select proper charge based on refrigerant type
Incorrect Bulb Location
Relocate the bulb to proper location
Incorrect Equalizer Location
Relocate the equalizer to proper location
Plugged Equalizer (Balanced Port Valve)
Remove any restriction in the equalizer tube
Superheat Is Too High -- TXV Doesn't Feed or Doesn't Feed Enough
Problem
Valve
Doesn't
Feed or
Doesn't
Feed
Enough
Symptoms
1) Evaporator Temperature Too High
2) High Superheat
3) Low Suction Pressure
Causes
Corrective Action
Short of Refrigerant
Add correct amount of refrigerant
High Superheat
Change superheat setting
Flash Gas In Liquid Line
Remove source of restriction
Low or Lost Bulb Charge
Replace power element or valve
Moisture
Replace driers or evacuate the system and
replace refrigerant
Plugged Equalizer (Conventional Valve)
Remove restriction in equalizer tube
Insufficient Pressure Drop or Valve Too
Small
Replace existing valve with properly sized valve
Dirt or Foreign Material
Clean out material or replace valve
Incorrect Charge Selection
Select correct charge
Incorrect Bulb Location
Move bulb to correct location
Incorrect Equalizer Location
Move equalizer to correct location
Charge Migration (MOP Only, Vapor
Charges)
Move valve to a warmer location or apply heat
tape to powerhead
Wax
Use charcoal drier
Wrong equalizer Type Valve
Use externally equalized valve
Rod Leakage (Balanced Port Valve)
Replace valve
Heat Damaged Powerhead
Replace powerhead or valve
No Superheat At Start Up Only
Problem
Symptoms
Valve Feeds 1) Liquid Slugging
Too Much At 2) Zero Superheat
Start Up
3) Suction Pressure Too High
Causes
Corrective Action
Refrigerant Drainage
Use pump down control; Install trap at the top
of the evaporator
Compressor or Suction Line in a Cold
Location
Install crankcase heater; Install suction solenoid
Partially Restricted or Plugged External
Equalizer (Balanced Port Valve)
Remove restriction
Liquid Line Solenoid Won't Shut
Replace powerhead or valve
Superheat Is Erratic Or Hunts
Problem
System
Hunts or
Cycles
Symptoms
1) Suction Pressure Hunts
2) Superheat Hunts
3) Erratic Valve Feeding
Causes
Corrective Action
Bulb Location Incorrect
Reposition Bulb
Valve Too Large
Replace with correctly sized valve
Incorrect Superheat Setting
Adjust superheat to correct setting
System Design
Redesign system
60
Superheat Appears Normal -- System Performs Poorly
Problem
Valve Doesn't Feed Properly
Symptoms
1) Poor System Performance
2) Low or Normal Superheat
3) Low Suction Pressure
Causes
Corrective Action
Unequal Circuit Loading
Make modification to balance load
Flow From One Coil Affecting
Another Coil
Correct piping
Low Load
Correct conditions causing low load
Mismatched Coil/Compressor
Correct match
Incorrect Distributor
Install correct distributor
Evaporator Oil-Logged
Increase gas velocity through coil
TROUBLESHOOTING SOLENOID VALVES
Problem
Normally Closed Valve Will Not Open
-orNormally Open Valve Will Not Close
Causes
Corrective Action
Movement of plunger or diaphragm restricted
a) Corroded parts
b) Foreign material lodged in valve
c) Dented or bent enclosing tube
d) Warped or distorted body due to improper
brazing or crushing in vice
Clean affected parts and replace parts as
required. Correct the cause of corrosion or source
of foreign materials in the system.
Improper wiring
Check electrical circuit for loose or broken
connections. Attach voltmeter to coil leads and
check voltage, inrush and holding currents
Faulty contacts on relays or thermostats
Check contacts in relays and thermostats. clean or
replace as required.
Voltage and frequency rating or solenoid coil not
matched to electrical supply:
a) low voltage
b) high voltage
c) incorrect frequency
Check voltage and frequency stamped on coil
assembly to make certain it matches electrical
source. If it does not, obtain new coil assembly
with proper voltage and frequency rating:
a) Locate cause of voltage drop and correct.
Install proper transformer, wire size as needed. Be
sure all connections are tight and that relays
function properly.
b) Excessively high voltage will cause coil burnout.
Obtain new coil assembly with proper voltage
rating.
c) Obtain new coil assembly with proper frequency
rating.
Oversized Valve
Install correct sized valve. Consult extended
capacities tables.
Valve improperly assembled.
Assemble parts in proper position making certain
none are missing from valve assembly.
Coil Burnout
a) Supply voltage at coil too low (below 85% of
rated coil voltage)
b) Supply voltage at valve too high (more than
10% above coil voltage rating)
c) Valve located at high ambient
a) Locate cause of low voltage and correct (check
transformer, wire size, and control rating)
b) Locate cause of high voltage and correct
(install proper transformer or service)
c) Ventilate the area from high ambient. Remove
covering from coil housing
d) Plunger restricted due to: corroded parts,
d) Clean affected parts and replace as required.
foreign materials lodged in valve, dented or bent Connect cause of corrosion or source of foreign
enclosing tube or warped or distorted body due to material in the system
improper brazing or curshing in vise
e) With valve closed, pressure difference across e) Reduce pressure differential to less than
valve is too high preventing valve from opening
300psi
f) Improper wiring. Inrush voltage drop causing
f) Correct wiring according to valve manufacturers'
plunger to fail to pull magnetic field due to:
instructions. Solder all low voltage connections.
- Wiring the valve to the load side of the motor
Use correct wire size.
starter
- Wiring the valve in parallel with another
appliance with high inrush current draw
- Poor connetions, especially on low voltage,
where connections should be soldered
- Wire size of electrical supply too small
g) Electrical supply (voltage and frequency) not
Check coil coltage and frequency to ensure match
matched to solenoid coil rating
to electrical service rating. Install new coil with
proper voltage and frequency rating.
61
Problem
Causes
Normally Closed Valve Will Not Close
-orNormally Open Valve Will Not Open
Corrective Action
Diaphragm or plunger restricted due to: corroded
parts, foreign material lodged in valve, dented or
bent closing tube, or warped body due to
improper brazing or crushing in vise
Clean affected parts and replace parts as
required. Correct the cause of corrosion or source
of foreign materials in the system. Install a filterdrier upstream of solenoid valve
Manual opening stem holding valve open
With coil de-energized, turn manual stem in
counter clockwise direction until valve closes
Closing spring missing or inoperative
Re-assemble with spring in proper position
Electrical feedback keeping coil energized, or
switch contacts not breaking circuit to coil
Attach voltmeter at coil leads and check for
feedack or closed circuit. Correct faulty contacts
or wiring
Reverse pressures (outlet pressure greater than
inlet pressure), or valve installed backwards
Install check valve at valve outlet, or install with
flow arrow in proper direction
Problem
Causes
Corrective Action
Foreign material lodged under seat
Valve Closes, But Flow Continues
(Seat Leakage)
Clean internal arts and remove foreign material
Valve seat damaged
Replace valve or affected parts
Synthetic seat materials chipped
Replace valve or affected parts
Valve improperly applied or assembled
Replace valve with proper valve or re-assemble
Special Considerations For Industrial Solenoid Valves
Symptoms
Causes
High Internal Seat Leakage (high temperature
steam up to 400°)
Corrective Action
Wrong Seat Elastomer Used (Buna N)
Use Valve with Teflon Seat Elastomer
External Leakage (high temperature steam up to
Wrong Gasket Material Used (Neoprene)
400°)
Use Ethylene Propylene Gasket
High Internal Seat Leakage (high temperature
steam up to 250° or water up to 210°)
Wrong Seat Elastomer Used (Buna N)
Use Valve with Ethylene Propylene Seat
Elastomer
External leakage (high temperature steam up to
250° or water up to 210°)
Wrong Gasket Material Used (Neoprene)
Use Ethylene Propylene Gasket
TROUBLESHOOTING BALL VALVES
Symptoms
Causes
Doesn't Flow
Corrective Action
Valve Isn't Open
Turn Stem
Leak at Access Schrader Valve
Schrader Valve Isn't Tight
Tighten Schrader Valve
Leak at Stem
Valve Stem is Leaking
Replace Valve
Excessive Pressure Drop
Valve Isn't Fully Open
Turn Stem to Open Valve
TROUBLESHOOTING SYSTEM PROTECTORS
Allowable Pressure Drop -- Permanent Installation
Evaporator Temperature
Refrigerant
40°F
20°F
0°F
-20°F
-40°F
R12, R134a
2.0
1.5
1.0
0.5
-
R22, R410A
3.0
2.0
1.5
1.0
0.5
R502, R404A/507
3.0
2.0
1.5
1.0
0.5
TROUBLESHOOTING STORAGE DEVICES
Suction Line Accumulators
Problem
Causes
Bleed Hole in U-Tube Plugged
Oil Not Returning to Compressor
Corrective Action
Replace Accumulator; Install Filter Ahead of
Accumulator
U-Tube Broken Off
Replace Accumulator
Accumulator Too Large for Application
Replace with Smaller Accumulator
Accumulator Installed Incorrectly
Re-Install with Correct Inlet & Outlet Connections
62
Liquid Refrigerant Receivers
Problem
Causes
Flashing In Liquid Sight Glass Downstream Of
Receiver
Corrective Action
Receiver Outlet Not Fully Open
Open Valve Fully
On Receivers with Top Outlet Connections, the
Dip Tube may be Broken Off Or Plugged
Replace Receiver
Receiver Installed Upside Down
Re-Install Receiver Correctly
TROUBLESHOOTING OIL CONTROLS - OMB
Problem
Causes
OMB out of calibration
Replace OMB
Too much oil in system
Remove oil from oil separator or reservoir until
proper level is maintained
Too much oil coming back from evaporator
Check system piping design for:
- Proper velocities
- P-traps at the bottom of all suction risers
- Piping pitched to compressor
- Overlapping or defrosts that are not staggered
Debris under solenoid valve seat
Unscrew solenoid valve from TraxOil; clean &
replace
Oil Level Too High In Sight Glass
Problem
Oil Level Too Low In Sight Glass
Problem
Causes
Corrective Action
Oil separator or reservoir empty
Add oil to maintain a liquid seal in teh bottom of
the serparator or reservoir
Plugged oil line filter
Replace filter
Plugged inlet strainer(s) on OMB
Remove and clean strainer on all affected OMB
Solenoid coil defective
Replace coil
Power loss to OMB
Check power to OMBl. Green light should be lit.
Causes
Corrective Action
Flood back through suction; Increase superheat
on expansion valve; Refrigerant condensing in oil
separator - add heater to oil separator and/or
adjust system setting to eliminate flood back
Liquid refrigerant in oil
Foaming In Sight Glass
Problem
Corrective Action
If so equipped, liquid injection overfeeding
Correct liquid injection overfeed
Excess quantity of oil in crankcase
Remove excess oil
Causes
Corrective Action
"Filling" light remains on even though level is 1/2
Replace OMB
above sight glass
Alarm light on all the time
Replace OMB
Intermittent oil return from system
Check system piping design for:
- Proper veloicties
- P-traps at the bottom of all suction risers
- Piping pitched to compressor
- Overlapping or defrosts that are not staggered
Nuisance Oil Alarms
TROUBLESHOOTING OIL SEPARATORS
Problem
Causes
Oil outlet valve closed or partially closed
Open oil outlet valve
Inadequate oil charge in system
Add oil in system
Oil float defective or dirty (will not open)
Disassemble and clean or replace defective float
component (flanged versions); Replace oil
separator (welded version).
Reduced or No Oil Feed to Compressor
Heat Gas Entering Compressor
Corrective Action
Separator too small for application
Replace separator with larger size
Oil float defective or dirty (will not close)
Disassemble and clean or replace defective float
component (flanged versions); Replace oil
separator (welded version).
63
TROUBLESHOOTING REGULATORS
Problem
Causes
Pilot inlet filter screen obstructed
Corrective Action
Clean or replace.
Erratic Pressure Control
Piston bleed hole restriction
Excessive dirt in pilot/solenoid
Regulator Will Not Open
(EPRBS Version)
Disassemble valve and clean. Replace if
necessary.
Piston bleed hole restriction
Coil is damaged or not energized
Verify coil is energized. Replace if necessary.
Piston bleed partially obstructed
Disassemble and clean regulator.
Excessive Pressure Drop Across the Regulator Pilot or solenoid leaking internally
Replace pilot assembly.
Refer to extended capacities table. Install correct
sized regulator.
Regulator undersized
Piston bleed port obstructed
Clean or replace.
Pilot inlet filter screen obstructed
Regulator Hunting-side Fluctuations in Controlled
Pressure
Regulator oversized
Refer to extended capacities table. Install correct
sized regulator.
Regulator and TXV have control interaction
Turn off pilot pressure. Ensure regulator is wide
open. Adjust superheat to required setting. Turn
pilot pressure back on.
Regulator and cylinder unloaders have control
interaction
The unloader should be set to control at least 5
psig lower than regulator.
Pilot inlet filter screen obstructed
Clean or replace.
Pilot inlet pressure is too low
Increase pressure ot a minimum of 25 psi higher
than the main valve outlet pressure.
Regulator Will Not Provide Pressure Control
Locate and remove the stoppage or dirt. Replace
Piston jammed due to excessive dirt; Inoperative
pilot. A broken diaphragm can be detected by
pilot or broken diaphragm
checking for leaks around the adjusting stem.
Regulator Will Not Close
(EPRBS Version)
Dirt under seat
Disassemble and clean.
Excessive piston seal leakage
Replace bell piston assembly.
Plugged pilot filter
Clean or replace.
Pilot supply turned off or restricted
Verify pilot inlet pressure is at least 25 psig
greater than valve outlet.
Excessive dirt in pilot/solenoid
Replace pilot assembly.
TROUBLESHOOTING HOT GAS REGULATORS
Problem
Causes
Low Suction Pressure - Valve Open
Will Not Bypass - Valve Not Open
Suction Pressure Swings Erratically
Bypass Continuously - Suction Pressure High
Setpoint Drifts
Corrective Action
Valve undersized
Replace valve with correct size
1. Solenoid (if present) not energized
2. Valve sticking closed
3. Not set properly
4. Bad pilot
1. Repair (replace solenoid coil)
2. Replace
3. Recalibrate
4. Replace
Oversized valve
Replace valve with correct size
1. Manual stem screwed down
2. Valve sticking open
3. Bad pilot
1. Back stem out
2. Repair/replace valve
3. Replace pilot
Bad pilot
Replace pilot
TROUBLESHOOTING CRANKCASE REGULATORS
Problem
Valve Won't Adjust or Is Erratic
Valve Throttles Constantly
Causes
Corrective Action
With system running, open the valve adjustment
to open the valve and flush away the contaminant.
If this fails, replace valve.
Dirt under seat
Re-adjust bypass and/or CPR valve so that the
On system equipped with Hot Gas Bypas Valves,
CPR setting is higher than the discharge bypass
the bypass valve setting is higher than CPR
valve
TXV with MOP feature used with the CPR
To improve pull-down time, replace TXV with
equivalent without MOP feature
Valve setting is too low
Re-adjust the CPR to a higher setting - see
adjustment procedure
Temperature Pull-Down After Defrost is Too Long
64
Problem
Causes
Compressor tripping on Internal Thermal
Protector - Fails to Start-Up and Run Long
Enough to Pull Down Temperature
Corrective Action
CPR setting too high
Re-adjust the CPR to a lower setting - see
adjustment procedure
CPR setting is too low
Valve Fails to Open
Valve defective - bellows leak, pressurizing the
upper adjustment assembly
Replace valve
TROUBLESHOOTING HEAD PRESSURE CONTROLS
Problem
Causes
Low Head Pressure During Operation
Systen Runs High Head Pressure
-orCycles on High Pressure Cut-Out
Corrective Action
Valve unable to throttle "C" port
1. Foreign material wedged between "C" port
seat and seat disc
2. Power element lost its charge
3. Insufficient winter-time system charge
1. Artificially raise head pressure and tap valve
body to dislodge foreign material
2. Change valve
3. Add refrigerant per Table 3
Wrong charge pressure in valve for refrigerant
Change valve
Receiver exposed to low ambient conditions is
acting as condenser
Insulate the receiver
Hot gas bypass line restricted or shut off
Clear obstruction or open valve
Compressor not pumping, restriction in liquid
line, low side causing very low suction pressure
Change or repair compressor; clear obstruction
or other reason for low suction pressure
Condenser fan not running or turning in wrong
direction
Replace or repair fan motor, belts, wiring or
controls as required
Fan cycling
Run condenser fan continuously while system is
running
Pressure drop through condenser exceeds
allowable 20 psi forcing "B" port partially open
Repipe, recircuit, or change condenser as
required to reduce condenser pressure drop to
less than 20 psi
Condenser undersized or air flow restricted or
short circuiting
Increase size of condenser or remove air flow
restriction or short circuit as required
"B" port wedged open due to foreign material
between seat and seat disc
Artificially reduce head pressure below valve
setpoint and tap valve body with system running
to dislodge foreign material
"B" port seat damaged due to foreign material
Change valve
Wrong charge pressure in valve for refrigerant
Excessive system charge or air in system
Purge or bleed off refrigerant or noncondensables as system requires
Obstruction or valve closed in discharge or
condenser drain line
Clear obstruction or open valve
Liquid line solenoid fails to open
Check solenoid
CHARGING THE SYSTEM - THEORETICAL METHOD
Weighing the Charge (Method has practical limitations)
Add refrigerant until the sight glass is clear and free of bubbles.
Determine refrigerant required to fill the condenser, see Table 3 below. Add this additional amount.
Table 3 - Refrigerant lbs. per ft.*
Condenser Tube Size - O.D. (in inches)** and Ambient Temperature ° F
Refrigerant
3/8"
40°
0°
1/2"
-20°
-40°
5/8"
40°
0°
-20°
-40°
40°
0°
-20°
-40°
R134a
.051
.054
.055
.057
.095
.099
.102
.105
.150
.157
.164
.167
R22
.051
.054
.055
.056
.094
.099
.102
.104
.150
.159
.163
.167
R404A/R507
.053
.056
.058
.059
.098
.104
.107
.109
.157
.166
.171
.175
* Return bends: 3/8” O.D. - 20 ft; 1/2 O.D. - 25 ft.; 5/8 O.D. - 30 ft.
** Wall thickness: 3/8” O.D. - .016”; 1/2 O.D. - .017”; 5/8 O.D. - .018”
65
Emerson Climate Technologies Flow Controls
St. Louis, Missouri 63141
(314) 569-4500
WEBSITE: www.emersonflowcontrols.com
E-MAIL: sales@emersonclimate.com
Form No. 2004FC-141 R2(4/06)
Emerson Climate Technologies and the Emerson Climate Technologies logo are service marks and trademarks of Emerson
Electric Co. All other trademarks are property of their respective owner. © 2004 Flow Controls. Printed in the USA.