Air Valve Selection

By Jeff Bready, CFPHS

“Air” – or pneumatic – directional control valves are available in an extremely wide variety of configurations and control options. Air valves, with a naming and describing system that counts how many port connections as well as how many flow paths through the valve are included, are commonly designated as:  2-way, 3-way, 4-way 4-port, and 4-way 5-port. These descriptions, along with the air valves’ drawn graphic symbol, indicate the combinations of air flow directions through the valves. The air flow paths may include compressed air, exhaust air, and the air utilized to control the movement of an air actuator.

Additionally, air valves have a large number of operators – or, what valve element causes the air valve to shift position. These control or “shifting” mechanisms typically include a choice of either electrically-operated or manually-operated. Within the electrically-operated shifting mechanisms are solenoids with either single or double AC or DC solenoid voltage and a range of power consumption (watts) selections. The range of manually-operated shifting mechanisms is even broader. They can include shifting through the use of an air pilot, cam, lever, roller, palm button, pendant, foot operator, spring, and selector.

Air valve selection must begin with the linear or rotary actuator that the valve is intended to provide the air to move. Full cycle sequence of operation, speed of movement, cycle time, dwell times, and condition upon valve failure are all considerations which help determine the most appropriate air valve for the application.

Like most applications in fluid power, air valve selection is not an “exact science”. That is, there is not necessarily only one combination of components which could be used to achieve a desired circuit cycle result. Two 3-way valves can frequently be used instead of a single 4-way valve. A 5-port 4-way may have additional exhaust features and flow which will make it the better choice rather than a standard 4-port 4-way. How the valve should “rest” when the circuit is in neutral will have a direct impact on whether a three-position valve is incorporated and what the center valve position should contain. Selection of the valve operator is always an important consideration – for both operational and spatial concerns.

And, finally, the valve’s physical size and flow characteristics must be considered. It is a mistake to simply “match” the valve’s port size to the actuator’s port size. While this choice might provide for an easier plumbing job, it could be that the specified valve is really too large and therefore an unnecessary expense.