Directional valves operate by compressed air. They are similar to hydraulic solenoid valves in that they both use pressure. However, the return port of a pneumatic valve, which uses air, is exhausted to the atmosphere. Pneumatic valves regulate the admission or release of air.

There are two general types of pneumatic valves: direct-acting and pilot-operated. Direct-acting pneumatic valves have a plunger that is in direct contact with the primary opening in the body. This plunger is used to open and close the orifice. The pilot-operated pneumatic valve, in contrast, works with a diaphragm rather than a plunger. This type of pneumatic valve uses differential pressure to control the flow of fluid. The air-venting valve opens to allow the pressure to equalize and permit the fluids to flow.

Important factors to consider when looking at pneumatic valves are proportionality, linearity, frequency response, repeatability, power consumption, leakage, life expectancy, and cost. Because pneumatic valves are designed to perform operations used to restrict, meter, and maintain the flow of liquid and gaseous materials, they are widely used in vastly different fields and industries.