STEAM TRAPS
Trap Basics
Whenever possible, steam traps should be located ~2 foot from, and
below the discharge of the equipment.
Strainers, whether built in or separate, are recommended with all
steam traps.
Install ball (or gate) valves before and after the steam trap to ease
maintenance by isolating the trap from the rest of the system.
Trap Basics
Unions should be installed between the isolating valves and steam
trap so that the trap can be easily removed and replaced as
required.
Blowdown valves are recommended at strainer outlet
A test valve or a sight flow indicator are recommended to determine
if system is operating and functioning properly
Pipe Scale & Dirt
When new piping is installed, chunks
of solder, fragments of metal parts,
packing, and even nuts and bolts are
often left inside.
In older piping systems, there is a
build-up of scale and dirt that can
break free and travel through the
steam system.
Pipe scale and dirt can permanently
damage steam equipment, especially
steam traps. To overcome this:
– Install a strainer prior to every
steam trap
– Utilize a dirt pocket in front of the
trap to accumulate dirt and scale.
Steam Main Drip Leg
Steam main drip pockets are recommended at every
horizontal and vertical change of direction in piping, and
in front of all equipment such as control valves, PRVs, or
shut off valves because these are natural collection
points.
The distance between drain pockets should decrease as
the steam main size increases because of the additional
amount of energy (water hammer) larger mains have that
could cause damage.
A rule of thumb for spacing drip pockets is the higher the
pressure or larger the main, the closer the spacing.
Steam Main Drip Leg
For steam main up to 6”, a full size drip leg should be
installed. Over 6”, a collecting leg of ½ of the pipe size
can be utilized, as long as it is not under 6”
The take off of the steam trap should be at a point ~3”
above the lower level of the drip leg, draining by gravity
Back Pressure Effect
The general rule of
thumb for calculating the
back pressure of
condensate lift
installations is 1psig
back pressure for each
2 foot of vertical lift. For
low pressures, use
1psig per foot for lift.
Bypass Loops
Bypass loops are needed when the trap capacity can
not meet the start-up requirements.
– CAUTION: Bypass could be inadvertently left open,
allowing large amounts of live steam to be lost when hot
running load is achieved.
Most steam trap manufactures discourage the use of
bypass loops. By selecting a trap with high start-up
capacity, the bypass is not needed.
Traps in Parallel
Parallel traps are used in critical process applications
where the unit can not be shut down for servicing. One
trap can be on while the other is serviced.
Good alternate to the bypass loop installation because it
eliminates the possibility of blowing live steam through
an inadvertently open bypass valve.
– Negative: More Expensive
Space Heating Equipment
In order to facilitate good drainage from the equipment, a
vertical leg (at least 12” long) should be installed on the
bottom of the equipment.
If the unit heater has a modulating valve on the inlet,
consideration must be given to the ΔP across the trap so
that there is always enough steam pressure to remove
condensate.
Space Heating Equipment
The installation of a vacuum breaker is vital whenever
steam is controlled to the unit heater with a modulating
control valve.
An air vent installed at the opposite corner from the inlet
steam supply helps remove air from the remote areas of
the equipment.
Shell & Tube Heat Exchangers
Optional vacuum breaker installed to allow free
drainage of condensate when system is off.
The air vent is used to remove the air that may
be introduced through the opening of the
vacuum breaker or from the steam supply.
Delta Element
Delta Cycle-Start up
At cold start up,
stem is full open to
allow high flow
capacity
Only one moving
part for simple
design
Delta Cycle-Closing
Stem starts to close
as condensate
temperature
increases
Flow will modulate
as condensate is
formed
Delta Cycle-throttle
Stem throttles shut
when condensate
reaches
temperature of
saturated steam
Expansion chamber
allows extra
capacity before shut
off
Delta Cycle-Shut off
Stem is tightly shut
when steam is
present
Single, open blade
design allows faster
response to
temperature
changes
The Delta Cycle
Blowing Steam vs. Flash Steam