The purpose of this report is to analyse the performance, challenges and benefits of using ON/OFF valves as a replacement for a conventional proportional valve in a hydraulic velocity servo system.
Two models are made: one with 4 ON/OFF valves and one with a single proportional valve. All valves are commercially available.
3 main challenges are identified in this replacement: a multi-variable switching strategy should be made, the fluid hammer effect will add pressure transients every time a valve is turned ON or OFF and the switching time for each valve will restrict the switching frequency.
It is shown that the commercial valves are too slow and they should be replaced. A sliding mode controller is designed for each system. It is shown that this control strategy, along with faster valves, has a better performance than the traditional proportional valve.