Flow control valve are used to control the speed of extension and retraction of cylinders.
Cylinder speed control is accomplished by adjusting the flow of air into and out of the cylinder. For air cylinders controlling the flow is usually done through the use of flow control valves.
Containing a metering needle and a check valve, flow control valves restrict the flow in one direction only. Air entering the valve in one direction is blocked by the check valve and is forced to pass through the needle valve. The setting on the needle valve is adjusted to determine the rate of flow. When the air flow is in the opposite direction it passes unrestricted through the check valve. The direction of the controlled flow is stamped on the body of the flow control valve for ease in installation.
To determine which direction to place the restriction, the pneumatic industry follows a rule of thumb. The rule is:
If in doubt, meter-out
The term ‘meter-out’ indicates that the air leaving the cylinder is controlled. By restricting the flow of air that leaves the cylinder smooth control can be attained. Restricting the flow of air into the cylinder (meter-in) will lead to chattering.
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