CFW supplies a variety of diverter valves and lean-phase pneumatic conveying solutions. Contact our sales engineers for more information.
Diverter valves are also known as switching valves, multiport or multiway valves. They control material flows by combining or splitting them. They are also used to regulate flows to different kinds of process equipment and can maintain a constant flow rate to sensitive machinery by varying the flow directed to other machinery.
It can be hard to choose between the many available kinds of diverter valves, but properly selecting one will reduce maintenance costs, improve conveying efficiency and ensure smooth operation. Your choice will depend on the following factors:
- Application: Valves can redirect a single material flow to two destinations (two-way diverger valves) – the most common application – or can be modified to combine two material flows towards one destination (two-way converger valves). Diverger valves can be altered to serve as converger valves, but this can be expensive. For some applications, multiport diverter valves, which can deal with more than two source or destination flows, are needed.
- Type of pneumatic conveying system: The choice of a dilute- or dense-phase system and negative or positive pressure system affects the pressure at which the valve needs to operate, and therefore its efficiency. The pipe diameter and pressure drops involved are also significant.
- Type of material conveyed: The particle size and abrasiveness of the material is important. Particles of the wrong size can pack and clog, become stuck, or leak into a closed downstream line. Abrasive materials can erode the valve and cause pressure drops or contamination. All this may result in expensive maintenance downtimes.
- Costs: These include the capital, shipping, installation, maintenance costs, as well as the possibility of production costs from improper functioning.
- Construction: The valve can be constructed of various materials (iron, aluminium, steel or other alloys) and may be actuated in various ways (manually, electrically, pneumatically etc.).
The rotary plug diverter valve (or tunnel diverter valve) uses a solid plug with a cylindrical hole through it to direct materials to one outlet of the valve or another. The plug rotates to direct material flows through the hole to the right destination.
A variant, the parallel-tunnel diverter valve, has two parallel holes. It suffers less valve wear because the degree of plug rotation can be reduced. Rotary plug valves do not usually handle powders, because powder can become lodged between the plug and its casing. Instead, they are used for pellets. The valve should not be shifted while conveying is taking place, as this can cause blockages in the upstream line. Rotary plug valves are suitable for both dense and lean phase applications and can be modified for abrasive materials in the case of dense-phase systems. Pressure drop is low, and the valves create no cross-contamination of materials if on-the-fly shifting is avoided and the materials are dust-free. However, the valves are some of the most expensive, as is their repair, and they are difficult to install. The seals wear down over time, resulting in material packing in the valve that requires cleaning the valve and replacing the seal.
Rotary-blade diverter valves have a metal plate that turns on an axis on its diameter, directing the direction of flow along the plate’s flat surface. On-the-fly shifting is still not advisable (the disc can trap materials in the sealing areas), but these valves are less subject to material packing and can be used for powders and small granules in dilute phase systems. This valve too can be used in either dense-phase or dilute-phase conveying and can be adapted for abrasive materials. They create low pressure drops, but are also expensive to buy and repair, and subject to seal abrasion.
Flapper diverter valves (or swing diverter valves) use a flapper on a hinge that swings to close one of the downstream lines. The hinge is placed between the two downstream lines. They can convey a wide variety of powder, granule or pellet materials, either in diverger or converger functions. They operate in both dense and lean phase systems. Changing between diverger and converger functions after installation requires expensive modifications. This valve is not suited to high-pressure dilute phase vacuum systems, because the flap can be pulled away from its seal. They have a limited ability to switch on the fly with certain powders, but there can still be problems with sealing if this is done.
This type of plug is lighter and much less costly than rotary-plug or –blade valves. The seals, however, are exposed to the material stream and can wear quickly, resulting in pressure loss, blockages or contamination. This makes them unsuitable for abrasive materials.
The sliding-blade diverter valve uses a blade that slides across the material flow. It has a hole in it so that material can pass through one of the two lines that intersect with the blade. This valve can handle powders or pellets for converger or diverger applications and lean or dense phase pneumatic conveying. It is capable of on-the-fly shifting in most cases. It is light, easy to install, and can be maintained in situ. However, it creates a bigger pressure drop than other valves and does not work as well if installed horizontally, as some material may get into the wrong downstream line.
Vertical, upward material flows work better because gravity will prevent material from getting caught on the upstream side of the blade. Sliding-blade valves are suitable for automated set-ups that allow for more than two destinations or sources.
Flexible-tube diverter valves consist of a flexible hose attached to a sliding blade that shifts the tube’s end (attached to a tube stub) to the appropriate downstream line. Like the sliding-blade diverter valve, it is flexible and usable in many contexts. Badly abrasive materials will wear out the tube. Some kinds of available seals permit on-the-fly shifting, while others do not. There is very little pressure drop and cross-contamination with this valve. However, problems can be caused because of pressure on the hose, which should be long enough to resist the stress of constant shifting. Like sliding-blade valves, flexible-tube valves can be used in automated set-ups involving multiple destinations or sources.
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