GB1425602A - Directional control valves - Google Patents

Abstract

1425602 Valves PARKER-HANNIFIN CORP 6 April 1973 [5 May 1972] 16632/73 Heading F2V A directional control valve for controlling two fluid motors has a pressure compensating piston 42 which, by by-passing any excess fluid, maintains a constant flow rate to the selected motor and in the event that both motors are selected for operation it provides for constant flow in the motor subject to the greater load. Fluid supply, via passage 43, is controlled by two spools 40, 41 the openings 59 in which are uncovered by the required amount to supply respective motors 50, 51 as the spools are displaced to the left or right from the neutral position shown and as fluid pressure operates secondary compensating pistons 60, 60 to uncover the orifices 61 in the spools 40, 41. At the same time check valves 62, 62 are unseated to permit pressure to be fed to the pressure compensating piston 42 via orifices 63 in the spool, passage 52 and restriction 53. Inlet pressure is fed to the chamber 57 at the other end of the pressure compensating piston via orifices 64 and 56 and the piston moves to a position to by-pass any excess flow so to maintain a constant pressure differential between the inlet pressure and that existing in the motor feed passage, i.e. to maintain a constant flow in accordance with the setting of the spool. If both motors are selected for operation the higher of the two pressures within the spool passages 68 will close the other check valve 62 to maintain the pressure in the chamber 54 of the pressure compensating piston at this higher level thus providing by-passing action in accordance with the flow to the more highly loaded motor and allowing the higher pressure to act on the secondary compressing piston 60 to control the flow to the corresponding motor. When both spools are in neutral, pressure in chamber 54 leaks away to exhaust via restrictions 53 and 58 and the piston 42 moves over to the right to provide maximum by-pass action, thus unloading the pump. Should pressure in chamber 54 becomes excessive under operating conditions valve 69 opens to provide an exhaust connection which causes piston 42 to provide an immediate relief action, restriction 53 preventing a build up of pressure in the chamber while valve 69 is open. In another embodiment, Fig. 3 (not shown), the fluid pressure for operating the pressure compensating piston (42<SP>1</SP>) is riot taken via the interconnecting passage 52 of Fig. 2 but via a check valve (78) in each spool giving access to the pressure in the axial bore of the spool upstream of the secondary compensating piston.