Fluid system and valve assembly therefor

Claim 1

A DIRECTIONAL CONTROL VALVE COMPRISING A HOUSING HAVING A BORE INTERSECTED AXIALLY THEREALONG BY INLET, CYLINDER, AND RETURN PASSAGES WHICH ARE ADAPTED TO BE CONNECTED, RESPECTIVELY, WITH A FLUID PRESSURE SOURCE, A FLUID MOTOR, AND A RESERVOIR; A VALVE SPOOL RECIPROCABLE IN SAID BORE TO POSITIONS SELECTIVELY OPENING FLUID COMMUNICATION BETWEEN SAID CYLINDER PASSAGE AND SAID INLET AND RETURN PASSAGES; STILL ANOTHER PASSAGE IN SAID HOUSING INTERSECTING SAID BORE, SAID ANOTHER PASSAGE BEING IN FLUID COMMUNICATION WITH SAID INLET PASSAGE WHEN SAID CYLINDER PASSAGE IS COMMUNICATED WITH SAID RETURN PASSAGE AS AFORESAID; A CHECK VALVE IN SAID CYLINDER PASSAGE OPENED BY FLUID PRESSURE WHEN SAID CYLINDER PASSAGE IS COMMUNICATED WITH SAID INLET PASSAGE; AND A FLUID PRESSURE ACTUATED PLUNGER MEANS IN SAID ANOTHER PASSAGE OPERATIVE TO BE MOVED TO A POSITION OPENING SAID CHECK VALVE WHEN SAID CYLINDER PASSAGE IS COMMUNICATED WITH SAID RETURN PASSAGE AND SAID ANOTHER PASSAGE IS COMMUNICATED WITH SAID INLET PASSAGE; SAID CHECK VALVE COMPRISING PILOT AND MAIN CHECKS OF WHICH THE FORMER HAS A RELATIVELY SMALL EFFECTIVE AREA AS COMPARED WITH THE EFFECTIVE AREA OF SAID PLUNGER MEANS, WHEREBY A LOWER PRESSURE ACTING ON SAID PLUNGER MEANS THAN ON SAID PILOT AND MAIN CHECKS TENDING TO CLOSE THE SAME WILL STILL BE EFFECTIVE TO CAUSE SAID PLUNGER MEANS TO OPEN SAID CHECK VALVE AS AFORESAID, THEREBY PERMITTING RETURN FLOW OF FLUID THROUGH SAID CHECK VALVE TO SAID RE TURN PASSAGE; SAID SPOOL HAVING METERING MEANS VARIABLY TO RESTRICT RETURN FLOW FROM SAID CYLINDER PASSAGE TO SAID RETURN PASSAGE AND THUS TO BUILD UP PRESSURE IN SAID CYLINDER PASSAGE TENDING TO OPPOSE MOVEMENT OF SAID PLUNGER MEANS IN A DIRECTION OPENING SAID CHECK VALVE; SAID PLUNGER MEANS BEING OPERATIVE FIRST TO ENGAGE SAID PILOT CHECK TO OPEN THE SAME AND THEN SAID MAIN CHECK IF THE FLUID PRESSURE ACTING ON SAID PLUNGER MEANS EXCEEDS THAT WHICH BUILDS UP IN SAID CYLINDER PASSAGE DUE TO METERING BY SAID SPOOL AS AFORESAID.