Using Steady Flow Force for Unstable Valve Design: Modeling and Experiments

In single stage valves, the main spools are stroked directly by solenoid actuators. They are cheaper and more reliable than multistage valves. Their use, however, is restricted to low bandwidth and low flow rate applications due to the limitation of the solenoid actuators. Our research focuses on alleviating the need for large and expensive solenoids in single stage valves by advantageously using fluid flow forces. For example, in a previous paper, we proposed to improve spool agility by inducing unstable transient flow forces by the use of negative damping lengths. In the present paper, how steady flow forces can be manipulated to improve spool agility is examined through fundamental momentum analysis, CFD analysis and experimental studies. Particularly, it is found that two previously ignored components viscosity effect and non-orifice momentum flux, have strong influence on steady flow forces. For positive damping lengths, viscosity increases the steady flow force, whereas for negative damping lengths, viscosity has the tendency of reducing steady flow forces. Also, by slightly modifying the non-orifice port geometry, the non-orifice flux can also be manipulated so as to reduce steady flow force. Therefore, both transient and steady flow forces, can also be used to improve the agility of single stage electrohydraulic valves.