GB1002331A - Improvements in or relating to compensating units for hydraulic actuating mechanisms - Google Patents

Abstract

1,002,331. Hydraulic apparatus. ARMSTRONG PATENTS CO. Ltd. Aug. 21, 1962 [Sept. 14, 1961], No. 32930/61. Heading F1P. A compensating unit for a hydraulic actuating mechanism having a pump connected in a closed circuit to a motor comprises first and second reservoir chambers 11, 12 arranged to be placed in communication with the circuit when the pump of the actuating mechanism is not in operation to accommodate changes in the volume of the circuit, the second chamber coming into use when the volume changes are too large to be accommodated by the first chamber alone. The unit is housed in a casing 5 in which is a passage 4 having threaded ends 6 for connection into one of the pipes of the mechanism. A passage 7 containing a ball valve 13 joins the passage 4 to a bore 8 from which branch passages 9, 10 lead to the chambers 11, 12. The ball valve 13 is normally urged to a closed position by a spring 15 but can be opened to connect the main passage 4 to the branch passage 9, 10 by manual rotation of a cam shaft 17 in the bore 8 displacing a push rod 16 which lifts the ball from its seating 14. The chambers 11, 12 are in the form of cylinders containing pistons 25, 26 connected together by a yoke 22, the piston 26 being urged upwardly by a spring 30 so that the piston 25 acts to pressurise the liquid in the branch passage at a valve lower than that in the main passage 4 when the pump is operative. The pressure in the branch passages urges a ball valve 32 in branch passage 10 on to its seating 33 to normally isolate the chamber 12. When the pump is not operative, the cam shaft 17 is rotated by a lever to cause the push rod 16 to open the ball valve 13 and connect the main passage to the branch passages 9, 10. If, as the result of a temperature increase, the volume of fluid in the circuit increases, a flow of fluid will occur from the main passage through branch passage 9 into chamber 11 moving piston 25 upwardly against spring 30. If the volume increase is such as to cause piston 25 to move to the top of chamber 11, a peg 27 on piston 26 abuts a push rod 35 to open ball valve 32 and permit fluid to pass into chamber 12 and through a passage 28 in piston 26 into the upper part 29 of the casing, the flow of fluid into chamber 12 reducing the pressure in chamber 17 so that its piston moves downwardly under the action of spring 30 and increases the pressure in passage 10 to re-seat the ball valve 32. If the volume of fluid in the circuit decreases as a result of a fall in temperature, the spring 30 moves piston 25 downwardly to cause fluid in chamber 11 to pass to the main passage 4. When the piston 25 reaches the bottom of chamber 11, the spring 30 is no longer effective and the pressure in passage 10 drops to permit valve 32 to open and fluid from chamber 12 to pass to the main passage 4. The casing may contain a second identical compensating unit for connection to the second pipe of the actuating mechanism, the cam shaft 17 being common to both units. When the unit is connected to an actuating mechanism which is load supporting when the pump is not operative, a hydraulic locking device, such as described in Specification 910,889, may be incorporated in the circuit. Specification 826,229 also is referred to.