Flow control valves are used to regulate the speed of an actuator. These function by defining a flow area and can be classified as adjustable and nonadjustable. They are rated by operating pressure and capacity. They can be used in meter-in or meter-out applications. There are two general types of flow control valves:
• Fixed orifice
When meter-in is used to control flow, the valve is placed in series between the control valve and the actuator. This method of flow control is used in hydraulic circuits that continually resist pump flow such as those used to actuate a dump truck ram. A meter-out flow control valve is required when an actuator has the potential to run away. The meter-out flow control valve would be placed between the actuator and the reservoir to control flow away from the actuator.
A bleed-off flow control valve is placed between the pump outlet and the reservoir and it meters diverted flow as opposed to working flow. The result is that metered flow is directed back to the reservoir at the load pressure rather than the relief valve pressure. Bleed-off-type control valves are the least precise means of controlling flow. A simple fixed restriction in a hydraulic circuit can be used to control flow when it is located in series so that it controls actuator speed by either diverting or slowing flow.