Comparison of hydraulic and pneumatic flow in a proportional solenoid valve

In serial testing of hydraulic solenoid valves as part of the manufacturing process, the use of liquid mediums poses various challenges, including inconvenient part handling, frequent exchange of fluids and expensive maintenance of machinery. The present study investigates the feasibility of using gaseous mediums as an alternative for hydraulic testing without compromising established hydraulic testing standards. Using an exemplary 2/2 hydraulic proportional valve, we carried out experiments using both gaseous and liquid mediums. The experimental data indicates a consistent correlation between the two fluids across relevant pressure levels, alongside an accurate reproduction of key variables. Based on these results, a generalized methodology for determining the applicability of pneumatic methods to test similar hydraulic valve types is proposed. Corresponding Computational Fluid Dynamics (CFD) analyses reveal that supersonic velocities occur in the contraction area during pneumatic testing, resembling characteristics often found in supersonic nozzle flows. The simulations further indicate considerable differences in the flow-induced forces among the two fluids in some regions within the flow domain. Nonetheless, critical testing parameters are not affected by these effects, therefore the correlation is preserved.