| 摘要 |
A valve spool characterized by significantly lower flow induced axial force, the force being sufficiently low to render single stage servomechanical valves practical for small and moderately powered servomechanical apparatus. The present valve spool and servomechanical apparatus has a zero force metering edge which results from selection of a slope for the exit portion of the flow contour which is between that of a prior art rectangular port and that of the shallow slope typical of large negative axial force design. The present valve spool is further configured to allow metering across a small portion of the spool circumference in order to increase valve stroke and to minimize spool leakage. Preferably, a wedge is cut on two of the metering spool edges by grinding symmetrical flats across the valve spool edge to form the metering edges, the metering orifice then being defined by the intersection of the insert edge and the valve spool flat. Use of a partial circumferential opening, such as a wedge cut, in combination with a low force flow contour results in a valve spool with long stroke, low axial flow force, negligible leakage, and which can be manufactured with low tolerances.
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