Selecting 2-Way Diverter Valves For Your Pneumatic Conveying System

Selecting a diverter valve for your pneumatic conveying application can be a difficult task, especially when you consider the different designs and manufacturers. Proper selection and application of diverter valves can offer improved plant efficiency, adding to a company’s overall profits while reducing downtime and maintenance costs.

 Factors to Consider

  •  Cost Issues: The purchase price of a diverter valve is only one of many cost factors to consider. Other cost factors are freight, installation, maintenance costs, and production down time. Material cross-contamination due to internal valve leakage is another cost issue that should be considered.
  •  System Design: System design will influence the selection of your diverter. Consideration should be given to issues such as product size or “footprint”. Air and/or material leakage past the diverter will affect system capacity and blower/line size calculations.
  •  Dilute or Dense Phase:  Consider whether the system is designed for dilute phase pneumatic conveying (vacuum or pressure) or dense phase pneumatic conveying. Dilute phase is defined as conveying line pressures to 15 psig/1 bar, while dense phase is pressure to 90 psig or 6 bars. Each manufacturer will pressure rate their particular diverter design. Accordingly, valve size can also determine system pressure capabilities.
  •  Material Handled: The characteristics of the material being handled should be considered as well as the materials particle size, weight, hardness, abrasiveness and flowability.
  • Actuators: Depending on system requirements and power availability, diverters may be selected with choice of actuators; manual, air actuated, electric motor actuators with choice of electrical enclosures and hydraulic actuators.
  • Safety: No matter which valve type is chosen for an application, make sure individual safety features are in place for each valve used. Ensure that all moving parts are shielded from pinch points.

This article analyzes four diverters commonly used in dilute phase, vacuum, and dense phase pneumatic conveying.

1.      Rotary Plug Diverters

A rotary plug diverter has an internal plug that rotates to align the inlet and outlet. To divert material to the opposite port, the plug is rotated approximately 150° causing what was the outlet port of the plug to align with the inlet of the housing and the plug inlet port to align with the outlet port of the housing.

 Benefits:
  • Material is not cross contaminated when conveyed through the same line.
  • Seals are outside of the material flow stream and protected from blast abrasion.
  • Line pressure drop is minimal.
Things to Consider:
  • Rotary plug diverter made from cast is costly to purchase, install and to maintain
  • Packing of powders between the rotating plug and external housing can cause the plug style diverter to bind.
  • Blower should be shut down before shifting ports on a rotary plug diverter, as the actuation will block the conveying line causing system back pressure.
2.      Flapper Style Diverters

vortex2A flapper style diverter uses a metal flapper that shifts to block one port and divert material and air to the open port. In some models, the flapper seals against a replaceable polyurethane liner. In other models, polyurethane is sandwiched between two metal plates to create a better seal.

Benefits:

 

  • Material can be diverted during a stream because both ports are not blocked during the shift.
  • Diverter is lightweight, therefore easier and safer to install.
  • Valve is inexpensive to purchase and to replace parts.

 

 

 

 

Things to Consider:

 

  • Flapper seals are exposed to material abrasion requiring seal replacement often.
  • Air and fine material leak past worn seals into the closed conveying line resulting in system pressure drops, cross-contamination, and potential line plugs.
  • Flapper loses its seal under high vacuum as the flap is “lifted” from the internal sealing surface.

 

 

 

 

 

3.      Sliding Blade Diverters

vortex3The sliding blade diverter is fabricated with an “orifice” machined in the blade, which slides between two hard polymer seal plates. Upon shifting, the orifice aligns with the conveying line selected, while the sliding plate blocks the opposite port.

Benefits:
  • Material can be diverted during a stream without the need to shut down system blowers or fans.
  • Diverter is lightweight and can be maintained without removing it from the conveying line.
  • Design allows for a wide variety of configurations to match unique piping patterns.
Things to Consider:
  • Valve limited to dilute phase pneumatic conveying.
  • Transition from inlet to outlet creates slight pressure drop.
  • Residual amount of material may not purge when shifting of ports resulting in cross contamination.
4. Flexible Tube Diverters

vortex4A flexible tube or hose style diverter uses the basic sliding orifice blade design. A tube stub is welded to an orifice style blade, and a flexible hose is then attached to the tube stub. As the diverter blade is shifted, the conveying line, a flexible hose, moves from one port to the other.

Benefits:
  • Very little pressure drop across a flex tube diverter.
  • Purging the conveying line prior to shifting the diverter eliminates material cross contamination.
  • Material can be diverted during a stream without the need to shut down system blowers or fans.
Things to Consider:
  • Severely abrasive applications will wear out the hose quickly.
  • Overall stack up height and hose support requires large “footprint”.
  • Exposed pinch points create a safety hazard if the hose is not totally encased.

 

 

Conclusion

 

Many types of 2-way diverter designs are available to handle a wide range of materials and application-specific requirements. No diverter can fit all applications, so it is important to do adequate research and check with multiple suppliers before you select which diverter is right for your pneumatic conveying system.

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