GB783172A - An improved hydraulic control - Google Patents

Abstract

783,172. Hydraulic machines. PULTRA, Ltd. April 29, 1954 [May 28, 1953], No. 14835/53. Class 69 (2). An hydraulically actuated valve reverses the direction of motion of a piston connected to a machine tool table at each end of the stroke of the piston upon the pressure in the supply conduit exceeding that in the return conduit by a - predetermined amount. A variable delivery pump 18 delivers liquid to a cylinder 13 through a conduit 15 and a reversing valve 17. In the position shown liquid is delivered to the end 20 of the cylinder, liquid from the end 19 passing to a reservoir through a conduit 22 and an unloading valve 23. A differential valve 29 is disposed between conduits 15, 22 and while the machine tool table- 10 is in motion the back pressure in conduit 22 is sufficient to keep the valve 29 in its right-hand position. When the table reaches a stop 36 the pressure in conduit 15 increases until valve 29 is moved to the left and liquid passes through conduits 28, 30 to move the reversing valve 17 to the left. The end 20 of the cylinder is thus put into communication with conduit 22 and end 19 with conduit 15, and the piston 27 of a pilot valve 26 is moved to the right. The pressure in conduit 15 falls to its operating valve and the differential valve returns to its initial position. When the valve 29 is actuated on the table contacting a stop 37 liquid is directed through the pilot valve 26 to move the reversing valve to the right.