Air Preparation 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, bi-directional or three-way. In a one-way configuration, the valve permits metered flow in one direction and free flow in the reverse direction. In a two-way configuration, the valve provides for metered flow in both directions. In a three-way configuration, the control provides flow control in three directions.