Experimental discussions on unsteady characteristics of restrictor with variable opening area to construct a dynamic model for poppet valve

The present paper intends to provide a mathematical model which can precisely predict dynamic performances of a hydraulic poppet valve. In order to obtain fundamental knowledge about unsteady characteristics of a variable restrictor required to build a model, the following two measurements were conducted. First, in a poppet valve with its opening area fixed, pressure drops across and flow rates through the restriction were precisely measured in an oscillating oil flow. Examination of hydraulic impedances of the restrictor and how they depend on the amplitude of oscillatory flow rate revealed that both a kinetically induced differential pressure and a delay of a non-linear pressure loss against the flow rate characterize an unsteady poppet valve flow, just as that was the case with an unsteady orifice flow in a pipe. Second, the unstady relatioship between the pressure drop, the flow rate and the poppet displacement was examined on the basis of their waveforms measured in a pulsating flow ; these three quantities vary, not independently but in such a mutually-related way as describing a slender loop extending closely along the steady-state characteristic curve. The formerly proposed dynamic model of a poppet valve has been modified with these findings incorporated, proving to be able to predict properly the frequency response between the pressure loss across and the flow rate through a poppet valve, which the former model was unable to.