Robert Harkin
Powder and Bulk Engineering
Selecting a diverter valve for your pneumatic conveying system can be a tough job, especially when
you consider how many diverter valves are on the
market. Yet a properly selected diverter valve can
keep your operation running smoothly, cut maintenance costs, and improve your conveying system’s
efficiency. After outlining factors you should consider to select a diverter valve for your system, this
article provides descriptions of commonly used diverter valves, how they work, how they’re applied,
and their pros and cons.
B
efore you can select a diverter valve for your pneumatic conveying system, you need to consider several factors: your application type, your conveying
system type, your material characteristics, valve cost, and
valve options.
Application type. Most diverter valves, also called twoway diverter valves, convey material from one source to
two destinations. In some applications, a two-way diverter
valve is installed backward in the line to convey material
from two sources to one destination. When used this way,
it’s called a two-way converger valve. However, be aware
that turning a conventional two-way diverter valve into a
converger valve may require the manufacturer to make
costly design modifications that will increase the valve’s
purchase price. It may be more practical to select a valve
specifically designed for converging.
If your system has more than two material sources or destinations, you need to consider how each diverter valve can be installed to meet your system’s design criteria as well as your
budget. One way to meet these constraints is to install a diverter valve with more than two ports, called a multiport diverter valve. [Editor’s note: For more information about
multiport diverter valves, see the later section “Multiplesource, multiple-destination diverter valve configurations.”]
Conveying system type. Your diverter valve choice will
depend on whether your pneumatic conveying system is
dilute- or dense-phase and operates under pressure or vacuum. A dilute-phase system can have a conveying line
pressure up to 15 psig or vacuum pressure down to 30
inches mercury, while a dense-phase system can have a
conveying line pressure up to 90 psig. Make sure the valve
you select will operate well in your conveying phase and
at your system pressure or vacuum.
You also need to consider your pneumatic conveying system’s pressure or vacuum capabilities and line diameter, as
well as the expected pressure drop across the valve, to help
determine the valve’s minimum and maximum size. This
ensures that the valve will function properly and efficiently after it’s installed in your system. To help you narrow the field, many manufacturers pressure-rate each of
their valves and provide a valve-sizing chart listing each
valve’s specifications and limitations.
Material characteristics. Consider your material’s characteristics, such as particle size and abrasiveness, to
choose a diverter valve that can handle them. Particles that
are too large for the valve you select can become jammed
between the diverter’s internal components, preventing
Copyright, CSC Publishing, Powder and Bulk Engineering
Factors to consider when selecting
a diverter valve
Material that’s too abrasive for your valve’s design can
erode the valve components, creating a gap for air and material to pass through into the closed line. Air passing
through this gap will create a pressure drop across the system that affects the system’s capacity. And material passing through to the closed line may contaminate your
finished product.
To fix these problems, you must shut down the conveying
system and remove the valve to either clean or replace its
internal parts. This creates lengthy production downtime,
increases maintenance and production costs, and reduces
your system’s efficiency. To prevent these problems, identify your material characteristics and choose a valve that
can handle them.
Cost. A diverter valve’s purchase price is only one of
many costs you need to consider. Others include shipping,
installation, and maintenance costs, material cross-contamination costs associated with internal valve leaks, and
lost-production costs caused by maintenance downtime.
You can discover these and other performance-related
costs by asking for information from users who have installed a particular valve in an application similar to yours.
Options. Depending on your material characteristics, you
can specify that a diverter valve and its components be
constructed of cast aluminum, cast iron, stainless steel, or
a specialty alloy. And depending on your pneumatic conveying system’s specifications and power availability, you
can often specify that a valve be actuated manually, by air,
or by an electrical motor. You can also specify a valve with
an air-controlled solenoid and position-indicating
switches.
Now, keep these selection factors in mind as you explore
the types of available diverter valves. The following information covers five common diverter valves: rotary-plug,
rotary-blade, flapper, sliding-blade, and flexible-tube.
Multiple-source, multiple-destination diverter valve configurations are also discussed.
Rotary-plug diverter valve
The housing of a rotary-plug diverter valve (also called a
tunnel diverter valve), as shown in Figure 1a, contains a
solid rotating plug with a smooth tunnel-like hole bored
through it. The material flows through the tunnel from an
upstream conveying line to one of two downstream lines.
To divert flow from one downstream line to the other, the
plug rotates on a central axis, like a dial, about 150 degrees
so that the tunnel’s previous outlet becomes the tunnel’s
new inlet and the tunnel’s previous inlet becomes the tunnel’s new outlet to the other downstream line. In another
version of this valve, called a parallel-tunnel diverter
valve, shown in Figure 1b, two parallel tunnels are bored
through the rotating plug. This reduces valve wear because the plug has to rotate only about 45 degrees to shift
the material flow from one downstream line to the other.
The rotary-plug diverter valve is typically used for handling pellets rather than powders because powder can
pack between the rotating plug and housing. Shifting the
valve on the fly (that is, diverting material flow while the
conveying system is operating) isn’t recommended because it can cause the valve’s upstream conveying line to
become completely blocked.
The valve can be used in dilute- and dense-phase applications and be pressure-rated based on your application
needs, typically up to 15 psig for dilute-phase pressure
conveying and down to 30 inches mercury for dilutephase vacuum conveying. Manufacturers can also modify
the valve to achieve higher pressure ratings, allowing it to
handle abrasive materials in dense-phase high-pressure
applications. The rotary-plug diverter valve can have a
precision-machined cast housing and heavy pipe flanges
for connecting the valve to the conveying line.
The primary advantages of the rotary-plug diverter valve
are its shallow material deflection angle, which creates a
low pressure drop in the pneumatic conveying system, and
its ability to handle abrasive materials in high-pressure
dense-phase applications. As long as the conveying line is
purged before conveying a different material, the rotaryplug diverter valve’s smooth-bore tunnel eliminates material cross-contamination when handling nondusty
granules or pellets.
The primary disadvantages of the rotary-plug diverter
valve concern its cost, susceptibility to seal abrasion, and
inability to shift on the fly. This valve usually costs much
more than other valves because its precision-machined
cast housing is expensive to fabricate, hard to install, and
costly to repair. Valve replacement parts are also costly.
The rotary-plug diverter valve requires clearance between
the housing and sealing surfaces in order to actuate. Because the valve’s sealing surfaces wear with each plug rotation, material can become packed in the clearance gap
and bind the plug, preventing the valve from operating
properly. To fix it, you must remove the valve, clean it out,
and replace the seal or housing.
Copyright, CSC Publishing, Powder and Bulk Engineering
the valve from fully closing off the specified downstream
conveying line or lines (the closed line or closed lines) to
air and material flow. Particles that are too small for your
valve can become packed between the internal components, binding the diverter, or the material can pass into the
closed line.
Figure 1
Rotary-style diverter valves
a. Rotary-plug diverter valve
Actuation direction to switch lines
Material flow
Closed line
Rotating plug
b. Parallel-tunnel diverter valve
Actuation direction to switch lines
veying line to another. A metal shaft runs though the housing’s center and lengthwise through the disc, supporting
the disc and creating its central axis. An externally
mounted actuator connected to the metal shaft triggers the
disc’s rotation, and material flowing from the upstream
conveying line hits the disc’s flat surface and is deflected
into the appropriate downstream line.
The rotary-blade diverter valve is typically used for granules and powders, especially in dilute-phase systems, because it’s less subject to powder packing problems than the
rotary-plug diverter valve. However, shifting on the fly
isn’t recommended because the valve’s rotating disc can
trap material in the sealing areas during the shift.
Like the rotary-plug diverter valve, this valve can be used
in dilute- and dense-phase systems and be pressure-rated
based on your needs, typically up to 15 psig for dilutephase pressure conveying and down to 30 inches mercury
for dilute-phase vacuum conveying. The valve can be
modified by the manufacturer to achieve higher pressure
ratings so it can handle abrasive materials in dense-phase
high-pressure applications. The valve can have a precision-machined cast housing and heavy pipe flanges for
connecting it to the conveying line.
The primary advantages of the rotary-blade diverter valve
are the same as those of the rotary-plug diverter valve: its
shallow material deflection angle, which creates a low
pressure drop in the pneumatic conveying system, and its
ability to handle abrasive materials in high-pressure
dense-phase applications.
Material flow
Rotating plug
Closed line
Parallel tunnel
The primary disadvantages of the rotary-blade diverter
valve, like those of the rotary-plug diverter valve, concern
its cost, susceptibility to seal abrasion, and inability to shift
on the fly. This valve usually costs much more than other
valves because its precision-machined cast housing is expensive to fabricate, hard to install, and costly to repair.
Valve replacement parts are also costly.
c. Rotary-blade diverter valve
Actuation direction to switch lines
Material flow
Rotating blade
Central axis
Closed line
The rotary-blade diverter valve requires clearance between
the housing and sealing surfaces in order to actuate. The
valve’s sealing surfaces tend to wear quickly when exposed
to abrasive materials at high velocities. This enlarges the
clearance gap and allows air and material to migrate into the
closed line, which decreases the conveying system’s air volume and can cause material cross-contamination.
Flapper diverter valve
The flapper diverter valve (also called a swing diverter
valve), as shown in Figure 2, uses a swinging metal flapper (or gate) to divert material flow from the upstream
conveying line to one of two downstream lines. A metal
shaft runs though the housing between the downstream
Copyright, CSC Publishing, Powder and Bulk Engineering
Rotary-blade diverter valve
The housing of a rotary-blade diverter valve, as shown in
Figure 1c, contains a flat solid-metal disc that rotates on a
central axis to divert material from one downstream con-
The valve can be used in both dilute- and dense-phase pressure conveying systems to convey powders, granules, or
pellets from one source to two destinations (diverter) or
from two sources to one destination (converger). However,
once the valve’s material flow direction has been established, it can’t be reversed without costly valve modifications. Most flapper diverter valves in dilute-phase vacuum
conveying systems are limited to low-vacuum applications. In high-vacuum applications, the flapper can lose its
seal because the vacuum tends to pull the flapper from its
internal sealing surface.
With some powders, the flapper diverter valve can shift on
the fly. However, even with these powders, some material
can become trapped between the flapper and sealing surface, creating a gap for air and material leakage into the
closed line. Shifting this valve on the fly is even less suitable for materials with large particles.
The flapper diverter valve’s primary advantages are that it
typically weighs less and costs less to purchase, install,
and maintain than the rotary-plug and rotary-blade diverter valves.
One of the flapper diverter valve’s disadvantages is that
because its seals are directly in the material stream, they
can wear rapidly when the valve handles even mildly abrasive materials. And as the seals wear, air and material can
leak past the seal into the closed line, potentially causing
conveying air loss, material cross-contamination, and line
blockages. When the valve handles an abrasive material,
the seals must be replaced more frequently, which can lead
to extended downtime and increased production losses.
Because worn seals are difficult, expensive, and time-consuming to replace, select a flapper diverter valve that can
be serviced without removing it from your conveying line.
Sliding-blade diverter valve
The sliding-blade diverter valve, as shown in Figure 3, diverts material flow via its flat, rectangular, sliding metal
blade with a hole near its center. The sliding blade is installed so that it intersects and extends beyond both downstream conveying lines. To divert the flow, an actuator
slides the hole over a downstream line and the airflow carries the material through the hole into the line. The sliding
blade’s solid section stops material flow to the other downstream line. The blade can be carbon steel, aluminum, or
stainless steel, and the hole is the same size as the downstream conveying lines’ inside diameter. The valve’s
wear-compensating seals consist of a polymer pressure
plate with a rubber or silicone backing. The backing
pushes the pressure plate against the sliding blade, eliminating gaps that would allow air and material to leak into
the closed line.
The sliding-blade diverter valve can convey both powders
and pellets from a single source to multiple destinations
(diverter) or from multiple sources to a single destination
(converger) in either pressure or vacuum dilute-phase conveying systems. Because the valve’s seals create a positive
seal across the closed line, the valve can shift on the fly
with most materials.
The sliding-blade diverter valve has a precision-fabricated
structural frame as well as fabricated plastic-tube or metal-
Figure 3
Sliding-blade diverter valve
Actuation direction to switch lines
Figure 2
Seal
Flapper diverter valve
Actuation direction
to switch lines
Sliding blade
Closed line
Material flow
Closed line
Airfoil
Flapper
Flapper hinge
Material flow
Copyright, CSC Publishing, Powder and Bulk Engineering
lines and lengthwise through the flapper’s bottom, creating a hinge point that allows the flapper to swing back and
forth. In some models, the flapper seals against a replaceable polyurethane liner. The flapper diverter valve can be
made with pipe flanges or stub ends (used with compression couplings) for connection to a conveying line.
The sliding-blade diverter valve is lightweight and easy to
install, and its simple design allows you to make maintenance and seal adjustments without removing the valve.
Additionally, the valve’s weldments are easily replaced if
abrasive material wears through them, eliminating the expense of replacing the valve’s entire precision-cast housing in abrasive applications.
One disadvantage of the sliding-blade diverter valve is
that material flowing through the blade’s hole creates a
slightly greater pressure drop across the valve than is typically produced in other valves. Another disadvantage is
that the valve doesn’t function well if installed horizontally because material may not be completely purged from
the closed-line segment between the upstream conveying
line and the blade’s upstream surface, creating the potential for material cross-contamination. However, installing
the valve vertically, so that the material flows upward,
eliminates this problem because gravity eventually pulls
any material from the segment.
A naturally occurring high-pressure airfoil (Figure 3) prevents most of the material from entering the closed-line
segment, deflecting it back into the material stream. However, the airfoil can’t completely prevent cross-contamination because a small amount of material can still find its
way into the segment if the valve isn’t installed vertically.
The flexible hose is typically constructed of abrasion-resistant rubber, polymer, or flexible steel and is often
housed in an open hose-support frame. Some manufacturers offer an enclosed hose-support frame to prevent material from spilling onto the plant floor if the hose fails.
The flexible-tube diverter valve can use one of two seal
arrangements. One is a wear-compensating seal, which
ensures that a positive air-and-material-seal is maintained
when shifting. This seal allows the valve to shift on the fly
and function in both pressure and vacuum dilute-phase
systems. The other is a pneumatic seal, which uses an inflatable seal to handle the high pressures in dense-phase
systems. With this seal, the valve can’t shift on the fly because the seal must be deflated before shifting and reinflated after shifting before the material flow can be
restarted.
One advantage of the flexible-tube diverter valve is that
very little pressure drop is created across the valve because
the sliding-blade design provides smooth valve actuation
and a positive air and material shutoff to the closed line.
The valve virtually eliminates material cross-contamination because the upstream conveying line can be completely purged before the valve is shifted.
However, to work effectively, the valve’s hose must be
long enough to endure the torsional stress caused by constant shifting. If the hose is too short, the constant shifting
will fatigue the hose and cause it to break. Hose length depends on both the conveying line’s diameter and the shift-
Figure 4
Flexible-tube diverter valve
Flexible-tube diverter valve
The flexible-tube diverter valve (also called a hose diverter valve), as shown in Figure 4, operates similarly to
the sliding-blade diverter valve to divert flow in a conveying line. A tube stub is welded directly above a sliding
blade’s hole, which is installed just like a sliding-blade diverter valve, and a flexible hose is attached to the tube
stub. The flexible hose is then attached to the upstream
conveying line. To switch the flow from one downstream
conveying line to the other, an actuator shifts the sliding
blade and flexible hose together.
The flexible-tube diverter valve can convey powders and
pellets from one source to two destinations (diverter) or
from two sources to a single destination (converger) in
pressure or vacuum dilute-phase and pressure densephase conveying systems. However, the valve isn’t suited
to handling severely abrasive materials because they will
wear the hose.
Material flow
Hose support frame
Flexible hose
Actuation direction to switch lines
Actuator
Tube stub
Sliding blade
Closed line
Copyright, CSC Publishing, Powder and Bulk Engineering
pipe attachment points, called weldments. The weldments
match the conveying line construction material and serve
as attachment points to connect the valve to the lines using
compression couplings or fabricated flanges. The valve is
available in two-, three-, and four-way configurations for
more cost-effective conveying system design.
Figure 5
Multiport valve configurations
a. Three-way diverter configuration
Material flow
Sliding blades
Multiple-source, multiple-destination diverter valve
configurations
In many applications, material must be conveyed from
multiple sources to multiple destinations. Traditionally,
this has been done with a manually operated hose-andmanifold station, which requires a worker to uncouple an
upstream line from one source and recouple it to a downstream line that carries the material to the required destination. But this manual method is less than ideal. Toxic or
hazardous materials can spill when the lines are uncoupled. Material can be contaminated if the upstream line is
coupled with the wrong downstream line. Workers can injure themselves when uncoupling and coupling lines.
Downtime for uncoupling and coupling the lines can decrease production rates.
One way to successfully automate this process is to combine and stack various two-, three-, and four-way diverter
valves, as shown in Figure 5. Because the operating principles of standard rotary-plug, rotary-blade, and flapper diverter valves don’t typically allow themselves to work in
these configurations, sliding-blade or flexible-tube diverter valves, or a combination of them, are typically used
to convey materials from multiple sources to multiple destinations.
Typically, a three- or four-way diverter valve assembly is
custom-manufactured for the application. The assembly
tends to be compact, making it easier to install than a hoseand-manifold station. The assembly is independently
mounted on a standalone frame so it can be transported
and installed as a single unit. The assembly can include
connections for compressed air, electrical power, and operator controls. Be aware, however, that the multiport diverter valve assembly has a high onsite installation cost.
PBE
b. Four-way converger configuration
Material flow
Sliding blades
For further reading
For more information on diverter valves, go to www.pow
derbulk.com, click on “Article Index,” and look under the
subject headings “Valves” and “Pneumatic conveying,” or
see Powder and Bulk Engineering’s comprehensive
“Index to Articles” in the December 2003 issue.
Robert Harkin, associate editor for Powder and Bulk Engineering, produced this article based on information from
diverter valve manufacturers. PBE especially thanks
Salina Vortex Corp. [3024 Arnold Avenue, Salina, KS
67401-8105; 785-825-7177, fax 785-825-7194] for information and valve illustrations, and Paul Solt of Pneumatic
Conveying Consultants [529 South Berks Street, Allentown, PA 18104; 610-437-3220, fax 610-437-7935 (pcc
solt@enter.net)] for his assistance in preparing this article.
Copyright, CSC Publishing, Powder and Bulk Engineering
ing distance — the larger the line diameter or the greater
the shifting distance, the longer the hose.