GB938910A - Pressure balanced hydraulic valve - Google Patents

Abstract

938,910. Valves. CESSNA AIRCRAFT CO. Jan. 9, 1962 [March 13, 1961], No. 839/62. Class 135. An hydraulic flow control valve including a spool-type valve element having a land cooperating with a port or land in the surrounding valve housing to form a flow control orifice between two valve chambers, and including passage means for directing fluid under pressure between the valve chambers so as to produce and transmit to the spool-type valve element a resultant axial Bernoulli force which is substantially equal and in the opposite direction to that produced by the flow through the flow control orifice. In the embodiment shown in Fig. 5, the valve spool land has a control surface 44 normal to the axis co-operating with the surface 48 of the housing land. When the valve is open, the Bernoulli force acts to move the spool to the right. The spool land is provided with a blind bore 43 from which lead passages 45 at an angle of 72 degrees to the spool axis and flow through these passages provide the equal and opposite Bernoulii force. The size, location and angle of the passages 45 is found by experiment. The embodiment shown in Fig. 6 illustrates the invention applied to spool valve having notches 58 which themselves reduce the Bernoulii forces acting on the spool valve as opposed to the normal land of Fig. 5. Passages 55 are provided as above to counteract these forces and the outlet of these passages are arranged so that the body land surface 60 begins to close these outlets prior to the complete closure of the notches 58.