Poppet valves which have a flange located on the top or around the skirt of a conical poppet, to compensate for the flow force, are widely used in oil hydraulic systems. This report is on an experimental study concerned with the effects of a flange on the compensation of flow force in poppet valves. The characteristics of flow rate, thrust force, the cavitation occurrence limit and noise were examined for several diverged flow and converged flow poppet valves, which had different poppet angles, different flange diameters, different distances between the flange and the valve seat, and different expanding angles for the down-stream chamber.
The results obtained by the experiments are as follows. (1) In diverged flow valves the flow force is sufficiently compensated for by the impact of the jet on the flange. (2) In diverged flow poppet valves, the flange causes change in the thrust force with a change in the valve lift to become nearly zero. (3) When the flange diameter is small and the flange location is near the seat, as in the case of a diverged flow valve, the flow force is not compensated for sufficiently. This tendency becomes clearer under cavitating conditions. (4) In converged flow valve with a flange, the flow force causes the valve to close. (5) The expanding angle of the down-stream chamber also has a large effect on the thrust force characteristics.

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The effects of a flange located on the top or around the skirt of a conical poppet to compensate for the flow force were studied. In the previous report, the effects on the characteristics of flow rate, thrust force and cavitation occurrence were clarified for typical poppet valves with different flange diameters, different poppet angles, different distances between the flange and the valve seat, and different expanding angles for the down-stream chamber. In this second report, the effect was studied more closely and the mechanics of the effect were revealed by examining a half cut model of a poppet valve which is cut in half and covered with a transparent perspex plate on the cut surface. The cavitating flow was photographed, the pressure distribution along the poppet surface was measured in detail, and the thrust forces were obtained by integrating the pressure distribution along both the whole and partial areas of the poppet surface. The results revealed by this examination are as follows. (1) In diverged flow valves the flow force is sufficiently compensated for by the rising pressure on the flange surface caused by the impact of the jet. (2) The change in the thrust coefficient caused by cavitation depends on the change in the pressure distribution along the flange surface. (3) Why the effectiveness of the flange, used for the flow force compensation, decreased as the flange location became closer to the seat (as in diverged flow poppet valves) was clarified. (4) In the converged flow poppet valves, the change in the location of the flange does not have a large effect on the thrust characteristics.

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