Air valves allow metered flow of fluid in one or both directions. Many of them allow for free flow in one direction and reduced or metered flow in the reverse direction. They are used in pneumatic circuits to regulate the rate of activation or exhaust of cylinders and other pneumatic devices.  Air valves can be configured in-line or at right angles.  In an in-line configuration the input and output ports are on the same axis.  In a right angle configuration the input and output ports are perpendicular.

Flow control choices for air valves include unidirectional (one-way), bi-directional (two-way) or three-way.  In a one-way configuration the valve permits metered (restricted) flow in one direction and free flow in the reverse direction.  In a two-way configuration the valve provides for metered (restricted) flow in both directions.  In a three-way configuration the control provides flow control in three directions.  Flow compensation is an important consideration.  Choices include noncompensated, pressure compensated, and temperature compensated.  In a noncompensated flow control the amount of flow that passes through the orifice and the pressure drop across it are directly related. Flow through the valve varies with the fluid viscosity and pressure across the valve.  A pressure compensated flow control maintains accurate output flow regardless of the input pressure, up to rated limits. The orifice is adjusted to compensate for pressure variations and maintain a set flow rate.  A temperature compensated flow control maintains accurate output flow regardless of the input temperature, up to rated limits. Sharp-edged orifices or expansion rates of dissimilar metals are used to maintain a constant flow rate.  Air valves may have adjustability.  Choices include adjustable flow or fixed flow.  Important performance specifications to consider include metered flow for gas or air, and maximum operating pressure.

Common features for air valves induce integral relief valve, integral bypass, integral check valve, meter in, meter out, tamper-proof, locking nut, and swivel. An integral relief valve is pressure limiting.  An integral bypass controls by diverting or bypassing excess flow.  A check valve offers resistance to flow in only one direction.  If the flow inlet to the actuator is controlled, it is a meter-in system.  If the actuator outlet is controlled, it is a meter-out system.  Tamper-proof controls have a feature such as a removable knob or lock to prevent inadvertent or unauthorized adjustment.  A locking nut on adjustment stem locks the metering setting.  Swivel air valves rotate or swivel for alignment on cylinder in any orientation.  Media choices include air, gas, and steam.  Mounting choices for air valves include cartridge, subplate or manifold, pipe or line mount, port mounted, or stacked or sandwich mount. 

Additional specifications to consider when searching for air valves include metered flow input connectors, free flow input connectors, adjustment, and operating conditions.