The increase in pump discharge pressure during non-operation (when the valve is not supplied with a control signal).

I am using a six-way, three-position directional control valve to manage two single-acting hydraulic cylinders connected to a mechanical system that simulates the lifting and lowering process of a forklift. However, when the system is not operational (i.e., the valve is not receiving a control signal), I am experiencing an issue with high pump pressure, even though the valve is designed to allow oil to flow back to the reservoir when not in operation. What could be the problem? Is there an error in the connections, and what is the appropriate method for controlling the valve to achieve stable lifting and lowering operations?

Answer 1

[Yifeng Tang]

One thing to try: add some volume to the P port of the pump, to avoid something known as "dry node".

[Zeko]

"Could you explain more, please?"

[Yifeng Tang]

See this documentation page: https://www.mathworks.com/help/hydro/ug/troubleshooting-fluids-models.html. Look for the word "dry node".

It'll be easier for the community to diagnose your issues if you can

1. post the actual model. parameters matter a LOT. the rest of the system also matters a LOT.
2. use a newer version of MATLAB, as many users may not have the exact R2018b version any more.

If you are able to use a newer version, please consider using the isothermal liquid domain, instead of the hydraulics domain. See this documentation page for more information: https://www.mathworks.com/help/simscape/ug/advantages-of-using-isothermal-liquid-blocks.html