Abstract
This paper studies velocity control of a low-pressure water hydraulic cylinder drive. Two different systems are used, one with a proportional 4/3-way directional control valve and one with a proportional flow control valve. Experimental results with the proportional directional valve show that good control results can be achieved with closed-loop control system. Compensation of system nonlinearities allows also open-loop velocity control, which gives quite good accuracy in constant conditions. However external load force increases the velocity error and when good accuracy is needed in varying load conditions, the closed-loop control system has to be used. The results with the flow control valve are not as good but on the other hand the price of the valve is lower, which supports the use of this valve if the accuracy demand is not so high.
