Patent GB-627726-A (GB)
Title: Improvements in and relating to hydraulic control valves
IPC: B30B15/18
Filed: 1946-11-22
Abstract: 627,726. Hydraulic presses. WALDIE, G. A., Nov. 22, 1946, No. 34747. [Class 69 (ii)] A control valve 25, Fig. 2, for use with hydraulic ram-circuits, which enables the direction of operation of the ram to be reversed at the end of a working stroke without shock, is of the type comprising (a) a valve casing 30 having a " first " inlet port 34 for the pressure liquid of the ram, at which the liquid pressure is at all times substantially proportional to that obtaining in the retraction chamber 14, Fig. 1, of the ram cylinder 10 to which pressure liquid is supplied during the non-working strokes of the ram plunger 12, a " second " inlet port 33, Fig. 2, for the pressure liquid of the ram, at which the pressure liquid is at all times substantially proportional to that obtaining in the advancing chamber 13, Fig. 1, of the ram cylinder 10 to which pressure liquid is applied during the working strokes of the ram plunger 12 and two distinct outlets 35, Fig. 2, and 36, 38 combined, associated respectively with the two inlet ports 34 and 33; and (b) a reciprocable valve-member 40 working within the valve casing 30 and having a " forward " stroke and a " return " stroke, the valve-member 40 being (1) continuously subject to the liquid pressure obtaining at the " first " inlet port 34 of the valve casing 30, the liquid pressure always tending to move the member 40 in the direction of its " forward " stroke, against an opposing yielding control 45 always tending to move it in the reverse direction, and (2) operative so to control the two outlets 35 and 36, 38 of the valve casing 30 as to provide a gradual release of the pressure liquid from the advancing chamber 13 of the ram cylinder 10 upon reversal of the ram and at the same time a by-passage of the liquid relatively to the ram until the release of pressure is complete. In a control valve of the above type the valve-member 40 has in the course of its " forward " stroke two successive positions-an " intermediate " position which it occupies momentarily, immediately the pressure in the retraction chamber 14 commences to build up, consequent on the reversal of the ram, and a " final " position which it occupies subsequently in the build-up of the pressure and thereafter, until in the course of the next working stroke of the ram plunger 12, the latter commences to operate under load and in that (a) at the moment of reversal of the ram, the valve-member 40 occupies an " initial " position at the end of its return stroke, in which position it cuts off communication between the two outlets 35 and 36, 38 and the respective inlet ports 34 and 33, the valve member 40 having been brought to the " initial " position by the yielding control 45 during the working-under-load portion of the working stroke of the ram plunger 12, consequent on the drop of pressure which, during the working-under-load portion of the ram working stroke, occurs in the retraction chamber 14, and (b) in the " intermediate " position of the valve-member 40, the latter opens communication between the " first " inlet port 34 and the outlet 35 and partially opens communication between the " second " inlet port 33 and the other outlet 36, 38, while (c) in the " final " position the valve-member 40 cuts off communication between the " first " inlet port 34 and the outlet 35 and fully opens communication between the " second " inlet port 33 and the other outlet 36, 38, the arrangement being one in which the valve 25 comprises only one reciprocable valve member 40 that is operable to control both the outlets 35 and 36, 38 of the valve. The portion 38 of other outlet has its degree of opening controlled by an adjustable tapered throttle valve 39. Upon energizing a solenoid 19, Fig. 1, a reversible hydraulic-pump 15 is adjusted by linkage 18 so that the pump delivers into a chamber at one end of cylinder 10 and withdraws liquid from the retraction chamber 14 at the other end of the cylinder, thereby enabling the differential ram-plunger 12 to descend under gravity and commence a working stroke. The advancing chamber 13 is also supplied with liquid from a surge tank 24 located over the cylinder 10 through a conventional pre-fill surge-valve 21. When the ram plunger 12 engages the work, pressure in the chamber 14 falls and closes the surge-valve 21, which is connected to chamber 14 by a conduit 22 incorporating a check-valve 23. The ram-plunger 12 is now forced downwards by liquid pressure from the pump until the stroke is completed. During the working stroke the low pressure in chamber 14 and hence conduit 27 is insufficient to actuate the valve 25 situated in the tank 24. To effect reversal of the ram plunger 12 the solenoid 19 is deenergized and reverses the pump supply, thereby increasing pressure in chamber 14 and hence conduit 27, which pressure is transmitted to the left-hand end of valve member 40 by channel 47. After a certain rightward movement, the valve-member 40 is topped in the " intermediate " position by a plunger extension 44 abutting a piston 51. Liquid from conduit 26 is conducted to the right-hand side of piston 51 by a conduit 52 and a check-valve 53, so that when the pressure in chamber 13 is sufficiently reduced the valve-member 40 moves to its " final " position and the liquid behind the piston 51 is discharged through conduit 52 and an adjustable choke valve 54 to the conduit 26. Another port 37 from the valve 25 enables any differences in displacement between the valve-member 40 and piston 51 to be made up from the tank 24. When the ram 12 completes its upward movement, an arm 20, Fig. 1, on the ram, actuates the linkage 18 and places the pump 15 in a neutral position. The weight of the ram maintains sufficient pressure to keep the valve-member 40 in the " final " position until the next actuation of the solenoid 19. In a modification, the piston 51, conduit 52, check-valve 53 and adjustable choke-valve 54 of valve 25 are dispensed with and communication between port 37 and the surge tank 24 is effected by an adjustable throttle valve. The Specification as open to inspection under Sect. 91 comprises also a modification in which the piston 51 is urged leftwards by a spring and the conduit 52 is replaced by a throttle-valve. This subject-matter does not appear in the Specification as accepted.