5 Ways to Control Hydraulic Cylinder Speed
5 Ways to Control Hydraulic Cylinder Speed
5 Ways to Control Hydraulic Cylinder Speed
Hydraulic cylinders are unique in that they are almost 100% volumetrically efficient, although they suffer losses due to mechanical efficiency. This means that almost all of the fluid filled into them results in proportional linear motion, but only a fraction of the pressure they require is to move their charge. Regardless, speed calculations with cylinders are quite accurate and make controlling the speed quite simple. Here are 5 ways to control hydraulic cylinder speed.
Metered Hydraulic Flow Control
The most common method of controlling the speed of a hydraulic cylinder is to limit the flow rate entering the operating ports. You can install metered flow control valves directly on the operating ports, along the operating lines, or behind the valve stack or manifold. For reasons I will explain shortly, it is imperative that the flow control use a reverse flow check valve to allow free flow through the operating ports.
Non-metered Hydraulic Flow Control
As you would expect from the description, and unlike the first example, metering prevents the liquid from leaving the cylinder to control the speed. The cool old adage, "When in doubt, measure out" should save you a lot of doubt. In some cases, reducing the dosage may cause pressure concentration, leading to possible leakage or malfunction. Never take measurements when the rod-side fluid is responsible for holding the load of a double-acting cylinder, which, when exposed to retraction pressure, will combine with the load pressure to increase the rod-side pressure to dangerous levels. The possibility of intensification is why working port needle valves are unpopular for hydraulic cylinders and require a reverse flow check valve.
Hydraulic Needle Valves
As we mentioned before, you need to be careful here. However, in many cases this is the most effective and cost-sensitive method of controlling roller speed. Without check valves, needle valves restrict flow in both directions, making them suitable for low-speed gravity applications.
Priority type 3 port Hydraulic Flow Control
This valve has a single inlet and dual outlet, and the adjustment controls the rate of flow exiting each of these ports. The priority (CF) port is usually pressure compensated. Manages the flow hierarchy so that if the incoming flow drops below the priority flow setting, the flow is no longer available on the third port (EF).
You'll often see all-in-one 3-port flow controls with built-in relief valves, making them perfect for controlling one or two actuators in the system. Be careful in applications where inlet flow is high and controlled flow is low; because all incoming flow is subjected to operating pressure and any excess flow is wasted as heat.
Hydraulic Proportional Directional Valves
A proportional valve changes spool position using variable power via a PWM controller. The spool contains metering notches to provide a metered flow, essentially working like double-needle valves. However, depending on the spool type, pump type and control circuit, energy loss can be reduced.
If the valve spool moves a little, the valve will flow a little. Pressure balancing, load sensing or advanced electronic control gives the proportional valve superior performance in controlling cylinder speed.
Regardless of the control method, it is always beneficial to provide your rollers with a method to control speed. Even a simple bore can control hydraulic cylinder speed, but its performance may be improved compared to more advanced methods such as proportional control.