Hydraulic Flow Control Valve

Flow-control or speed-control valves are used to control the volume of oil that passes a given point. A flow-control valve is a metering valve and a check valve built into one housing. The volume may be controlled as it approaches a component or as it leaves a component. The design of the metering valve may vary from a needle to a cam-shaped device.

Cam-operated, flow-control valves are of value where flow control is only required for a portion of the cylinder stroke. They can be used as a cushioning device to provide extra long cushioning for a cylinder or for slip feeding arrangements by placing multiple cams on a trip bar. The one disadvantage of this type of valve is that the orifice must be designed for each size of pump as there is no adjustment means available.
Flow-control valves are normally built in sizes from ¼ -inch up to 2-inch pipe size. The majority are built for 1500 lb per sq in. maximum pressure but a number are available for much higher pressures.

Uses of Hydraulic Flow Control Valves

Basically hydraulic flow control valves are expected to control:

• Stopping of flow
• Direction of flow
• Flow media pressure
• Flow quantity

Flow-control valve gives trouble due to one of the following reasons:

1. If they are placed incorrectly or backwards in the circuit- This occurs inspite of the fact that they are usually marked with a large arrow showing the direction of the controlled flow.
   
   
2. Dirt lodging in the orifice causes it to clog up and produce erratic feed. Dirt under the check valve seat does not allow the check to seal off thus producing leakage.
   
   
3. A considerable change in oil viscosity has a definite effect on the flow-setting, especially on a needle-type metering device.
   
   
4. Excess internal leakage produces poor flow control. In this case, if the leakage becomes too much, it is possible that even changing the setting on the needle from one extreme to the other will not change the flow rate appreciably.