Dynamic Measurement of Valve Lift Force

The paper describes tests carried out on disc valves in which the valve seat was withdrawn from the valve wh).le a pressure difference existed across the valve. Simultaneous measurements were made of the force on the valve, the pressure in the plenum chamber and the displacement of the seat from the valve. Force measurements are compared with values of force measured during continuous flow conditions at selected values of pressure difference and displacement of the valve from its seat. The comparison may, therefore, be considered as relating the force on the valve during dynamic withdrawal of the seat from the valve to the quasi-steady state force on the valve at corresponding pressures and displacements during steady continuous flow through the valve. It is shown that during the early part of the withdrawal, there are significant differences between the force on the valve and the quasi-steady state force. 'J'hese differences are accentuated by the pressure difference across the valve and the rate at which the valve is opened. The quartz crystal force transducer being mounted directly on the valve had a sufficiently high natural frequency to be excited by small variations in the force on the valve at high frequencies due probably to vortex shedding at the periphery o:f the valve. The vortex shedding indicated by the force variations is now being investigated using hot wire anemometry techniques. The resonancesor peaks exhibited in this fluctuating component could be due to detachment and re-attachment of the air flow from the valve seat but, equally, could be due to coincidence of the frequency of vortex shedding w:lth the natural frequencies of vibration of the measurement system. Concurrent with this work, investigations are px·oceeding into the relationship between the force on the valve and the quasi steadystate force under conditions of continuous oscillation of the valve and in the presence of a pressure difference across it.