Steuereinrichtung fuer doppeltwirkende Hydraulik-Zylinder

摘要

985,950. Valves. HYDRAULIC UNIT SPECIALTIES CO. Aug. 16, 1962 [April 30, 1962], No. 31476/62. Heading F2V. [Also in Division G3] An hydraulic control valve has a body with an inlet 18, Fig. 1, an outlet 22, a pair of service passages 13, 14, Fig. 2, connectible with a reversible hydraulic motor, a spool 12 slidable to either of a pair of operating positions at each of which one service passage communicates with the inlet while the other communicates with the outlet, a U-shaped return fluid passage 33, and a check valve 42 which opens a by-pass 41 when the pressure in the return fluid passage 33 is higher than that in the service passage connected to the inlet. Cavitation during rapid operation of the motor by its load is thus prevented. In the preferred embodiment, two spools 12 for parallel or series-parallel operation of a pair of motors are mounted in separate parts 8, 9 of a body of sectional construction, and in their neutral position, permit fluid from the inlet to flow direct to the outlet through an open-centre passage 21. Movement of one of the spools to an operating position causes fluid from a feeder passage 26 to flow through a check valve 29 and a bridging passage 27 into one of the service passages, the other service passage being connected with the return fluid passage 33 which communicates with the outlet 22 through restrictions 37 and an exhaust manifold 32. The restrictions 37 raise the pressure in the passage 33 during rapid operation of the motor to ensure opening of the check valve 42 which has an annular shoulder 50 subjected to this pressure and a hollow interior accommodating a loading spring 48 and subjected through a port 49 to the pressure in the inlet service passage. Decreasing pressure in the latter opens the valve further so that a constant pressure drop from the passage 33 is maintained. In a modification, the passage 33 is connected to the manifold 32 by a valve 137, Fig. 4, which is identical in construction with the valve 42 and replaces the restrictions 37. Moreover, the valves 42 may be replaced by combined check and high pressure relief valves 70 of the type described in Specification 960,533 or a combined valve of the type described in Specification 950,131 may be used in place of the valves 42 and 137.