SPOOL VALVE ASSEMBLIES

摘要

1420417 Valves PARKER-HANNIFIN CORP 29 March 1973 [19 April 1972] 15257/73 Heading F2V A spool valve for controlling a double acting fluid motor 8, e.g. for raising and lowering the boom 22 of a bulldozer or a front end loader, comprises an inlet port 3, a return port 5 and motor ports 7, and has its spool 10 provided with passage means therein. Upward movement of the spool from its neutral position shown causes the motor to lower the boom 22, actuating oil being delivered from pump 4 to the head end of the motor via port 3, lower check valve 15, spool groove 35 and lower port 7, and return oil from the rod end of the motor being delivered via upper port 7 and ports 25 into the interior of the spool where it can unseat check valve 30 and pass into lower passage 12 to supplement the pump output and thereby prevent cavitation at the motor head end. When the bulldozer blade 21 contacts the ground, consequent pressure build up at port 3 closes the check valve 30 whereafter the return oil builds up sufficient pressure to open a relief valve 23 and flows through upper passage 17 and port 5 to storage tank 6. Downward movement of the spool reverses the connections to the motor so that actuating oil is supplied to the motor via passages 28, 25, upper check valve 15 and upper port 7, and return oil passes through lower port 7, spool groove 35, lower passage 17 and port 5 to the tank 6. Raising of the spool beyond the "lower" position to the "float" position causes the motor ports 7 to be connected to the upper and lower return passages 17 via respective spool grooves 38, 37. A main relief valve 13 is provided.