5 Factors to Consider When Choosing...

Pneumatic Control Valves

You have many options at your disposal when it comes to selecting a pneumatic directional control valve for your application. Each type of pneumatic control valve has a specific function, so it is important to understand the differences and select the type that best suits your requirements.

To help you arrive at the valve “type” that’s right for your pneumatic application, this article will highlight five basic requirements to consider:

Media
Method of Valve Actuation
Spring-Return Valve or Detented Actuation Valve?
Pneumatic Valve Configuration
Flow Capacity (Valve Size)

Media

Ensure that a valve is compatible with the media and its pressure before checking other factors. Here are some questions to consider.

What gas or liquid will be regulated by the pneumatic control valve?
What is the media’s input pressure?
Is the media compressed air, water, negative pressure or gas?

Method of Valve Actuation

There are various methods to open and close a pneumatic control valve. The four most common methods of valve actuation are:

Solenoid operated (via electrical current)
Manually operated (by skilled labor via a lever, pushbutton, foot peddle, etc.)
Mechanically operated (via tooling or workpieces in contact with a cam, ball or plunger)
Remote air operated (via an output signal from another valve)

Spring-Return Valve or Detented Actuation Valve?

The return method on a pneumatic valve takes the valve back to its original, unactuated state. The mechanism is usually a mechanical spring or a separate form of the same actuation method. Manufacturers call those methods spring-return and detented valve types.

Spring-return valves provide momentary contact and momentary output. Detented actuation valves deliver momentary contact for maintained output.

You will need to decide whether you want your valve to return to its initial position or stay in its final position after actuation.

Pneumatic Valve Configuration

Most pneumatic directional control valves are 2-, 3- or 4-way configurations, which account for their active media ports.

2-way valves: These valves have one INLET and one OUTLET port. Upon actuation, the valve allows media to pass through (2-way Normally Closed) or stops the flow of media (2-way Normally Open).
3-way valves: These valves add a third port (EXHAUST) to vent pressure at the OUTLET port when the INLET port is blocked. A 3-way valve is available in Normally Closed or Normally Open configurations.
4-Way Valves: This valve adds a second OUTLET and corresponding second EXHAUST port to the 3-way function. Most 4-way valves are used for controlling double-acting pneumatic cylinders and actuators. Upon actuation, the 4-way valve INLET pressure switches from one OUTLET port to the other.

Additionally, 4-way valves can be configured in three positions with the center position as a “neutral” position choice of three OUTLET options (exhausted, pressurized or checked).

Flow Capacity (Valve Size)

An undersized valve will slow fill time in the system, while an oversized valve wastes media. It’s important to estimate a maximum flow capacity for your application and select the appropriate valve size. All valve suppliers provide flow capacity specifications with reference material to assist you. Your valve must fill a specific downstream volume within an allotted period.

Tip: Most manufacturers state a “Cv” value, a universally accepted flow capacity index known as the flow coefficient. That allows you to compare similarly sized valves.