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.
Flow-control valve gives trouble due to one of the following reasons:
- 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.
- 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.
- A considerable change in oil viscosity has a definite effect on
the flow-setting, especially on a needle-type metering device.
- 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.
The flow control valves could be either:
a) throttle valves or flow restrictors that are pressure dependent
b) flow control valves that are pressure independent.