Abstract
In designing spool valves which are widely used in hydraulic power systems, one of the most important problems is to estimate the axial force exerted on the spool of the valve. This axial force can easily be estimated from momentum theory if the geometrical shape of the jet issuing from the metering orifice of the spool valve can be obtained.
In the present paper, a two-dimensional variable orifice was designed to observe the flow near the metering orifice of a spool valve. This orifice was partly made of transparent acrylic resins. The steady jet issuing from the metering orifice was visualized by means of air bubble method. The unsteady jet was also visualized by varying the width of the orifice sinusoidally. Photographs of the unsteady jet were taken by a high speed camera (16mm movie camera).
