GB1360446A - Hydraulic device with back pressure isolation - Google Patents

Abstract

1360446 Power hammers WORTHINGTON CORP 3 Nov 1971 [9 Nov 1970] 51101/71 Heading B3H An hydraulic hammer has its piston 18 pressurized constantly with hydraulic fluid on its lower face and alternately connected to a fluid source or an exhaust on its upper face and the passageway to the exhaust has a Venturi so that the back pressure against the upper face during an up-stroke of the piston is maintained relatively constant. The fluid inlet 34 is connected to the hammer cylinder bore by a port 42 and through grooves 45 in the cylinder wall to the lower face 44 of the piston and by a port 46 and a slide valve 50 to the upper face 58. The chamber 56 is alternately connected to an outlet port 64 by the slide valve whose reduced diameter portion 52 has an annular projection 72 which form the Venturi with the bore 54 when the valve is open. The valve is controlled by differential pins 66, 68. The pins 66 have a smaller effective area than the pins 68 and the pins 66 are connected constantly to inlet pressure whereas the pins 68 are only intermittently connected to the inlet pressure. A by-pass conduit 80 is automatically opened by a valve 82 to connect the inlet and outlet when the tool 28 of the hammer is in its lowermost position and hence not in contact with the work. The valve 82 is operated by differential pressure on surfaces 94, 96, 98 of the valve so that if the surface 98 is connected to exhaust by an overlong stroke of the hammer the valve automatically opens. The tool 28 is held in the hammer bore by a ball 32. The tool may perform the working operations or be an anvil in contact with a separate tool. The hammer may be used in demolition work.