Inherent Non-Linear Effects in Hydraulic Control Systems with Inertia Loading

The paper considers the inherent non-linear effects of inertia load on the performance of a pilot valve and ram system. Such a system may be considered as a model for many valve and ram or valve and motor combinations which are found in hydraulic control systems, and the results are therefore expressed in generalized form. It is shown that cavitation can occur dynamically when linear analysis would predict that only l/√2 of the static stalled effort is being utilized. Prior to cavitation there is surprisingly little distortion and attenuation of the velocity wave form of the ram when the valve is moved sinusoidally. The beneficial effects of exhaust lap are discussed and the paper goes on to develop and qualify the analysis when compressibility, friction, leakage, symmetrical lap and dither are introduced. Experimental results are compared with the theoretical predictions and the paper includes a note on the validity of small perturbation theory for this type of problem.