How to control the speed of a hydraulic cylinder?

Release Time :

2025-01-23

Throttling Flow Control – The most common method of controlling the speed of a hydraulic cylinder is to restrict the flow into its workport. You can install a throttling flow control valve directly at the workport, along the workline, or after a valve bank or manifold. Flow control must employ a reverse-flow check valve to allow free flow out of the workport for reasons I will explain shortly.

Throttling Flow Control – As you would expect from the description, throttling, in contrast to the first example, blocks the flow of fluid out of the cylinder to control speed. The old pneumatic adage “When in doubt, throttle” should give you a lot of pause. In some cases, throttling can cause pressure buildup, which can lead to leaks or failures. Never throttle when the rod-side fluid has the task of carrying the load of a double-acting cylinder, because when subjected to retract pressure, it will combine with the load pressure to raise the rod-side pressure to dangerous levels. The possibility of pressure buildup is why workport needle valves are unpopular in hydraulic cylinders, so reverse-flow check valves are required.

Needle Valve – As mentioned earlier, you need to be careful. But in many cases, it is the most effective and cost-sensitive method of controlling cylinder speed. Needle valves have no check valves and restrict flow in both directions, making them ideal for slow-speed gravity descent applications.

Priority-type 3-port flow control— This valve has a single inlet and dual outlets, with adjustment controlling the ratio of outflow from each port. The priority (CF) port is usually pressure compensated. It controls flow gradation, so if the inflow falls below the priority flow setting, there is no more flow from the third port (EF).

You will often see one-piece 3-port flow controllers with built-in relief valves, making them ideal for controlling one or two actuators in a control system. In applications where the inlet flow is high and the control flow is low, be aware that because all the inflow is subject to the operating pressure, any excess flow is wasted as heat.

Proportional directional valves— Proportional valves use variable power to change the spool position via a PWM controller. The spool contains metering grooves to provide metered flow and works in much the same way as a dual needle valve. However, energy losses can be reduced depending on the spool type, pump type, and control circuit.

If the spool moves a little, the valve flows a little. Pressure compensation, load sensing or sophisticated electronic control give proportional valves superior performance for controlling cylinder speed.

Regardless of the control method used, it is always helpful to provide the cylinder with a way to control speed. Even a simple orifice can control the speed of a hydraulic cylinder, although performance may be compromised compared to more advanced methods such as proportional control.


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