GB1098010A - Pilot governed control valve mechanism - Google Patents

Abstract

1,098,010. Hydraulic control circuits. HYDRAULIC UNIT SPECIALTIES CO. Nov. 8, 1965 [June 30, 1965], No. 47267/65. Heading F1P. A circuit for controlling the direction and speed of a double acting hydraulic piston 4 Fig. 1 comprises a closed centre spool valve 12 having an inlet 21, connected to the outlet of a pump 9, a return passage 33 connected to a reservoir 10, service passages 28, 29, connected to opposite ends of the cylinder 4, a main valve-controlled by-pass 74, 87, 16, 100, 31 Fig. 2 connecting the inlet passage 21 to the reservoir 10 and an auxiliary by-pass 82, 98, 97, 99, 47, 48, 49, 50 connecting said inlet 21 to reservoir 10 and including restriction means e.g. the spool 44 of a manually adjusted open centre pilot valve 13; the valve member 70 controlling the main by-pass being subjected at one side to the inlet pressure and at the opposite side to back pressure in the auxiliary by-pass generated by the restriction and which controls the degree of opening of valve 70 in accordance with the displacement of spool 44 whereby flow through valve 12 in one or other end position to the cylinder 4 is variably controlled. In operation and on moving the spool 44 to the right so as to block passage 48 and completely close valve 70, pressure in passage 47 opens a check valve 45' and gains access to a service passage 51 and to a line 53 leading to outer end of an actuator 17 which displaces the main valve spool 19 from its neutral position to its "raise" position thereby connecting the inlet 21 through a bridge passage 25 to the service passage 28 and to the head end of cylinder 4, whilst the rod end thereof is connected through passage 29 to the return passage 33; the piston 5 and rod 6 being moved at maximum speed. Reduced speed of operation is effected by so positioning the spool 44 that limited flow occurs from inlet 47 to outlet 49 through metering slots in the associated land of spool 44. Valve 70 has a skirt position 71 in which is housed a poppet valve 92 through which auxiliary by-pass portion 98 passes and which opens at an unduly high back pressure thereby venting the skirt interior to reservoir and allowing valve 70 to be unseated to relieve pressure from inlet 21. The valve 70 also acts as a "void" control valve in that it opens when pump delivery pressure falls below reservoir pressure. In a modification the main valve spool (190) Fig. 3 (not shown) may be hydraulically shifted to the left of neutral beyond its load lowering position to a "float" position at which both service passages 28, 29 are connected to the return passage; the left hand actuator 17 having a hydraulically actuated stop (109) which is withdrawn when the spool is to be moved to the "float" position. In a further modification the main valve spool (290) Fig. 4 (not shown) is movable by the pilot valve (230) to positions wherein the load is lifted at slow and fast speeds and is lowered at said speeds.