GB842452A - Improvements in piston pumps, more particularly for hydraulic pit props - Google Patents

Abstract

842,452. Hydraulic pit props. RHEINSTAHL WANHEIM G.m.b.H., No. 33523/56. Class 20(2) [Also in Group XXVIII] A reciprocating pump for extending a telescopic pit prop, comprises a low pressure piston 49 and a high pressure piston 50 and the low piston can be rendered inoperative at a predetermined pressure by a control cylinder 60 acted upon by the pressure in the pressure chamber 59 and the control cylinder 60 constitutes the inlet valve member for the low pressure piston. The low pressure piston 49 and the high pressure piston 50 are formed as a common piston body 48. The control cylinder 60 is arranged on the piston rod 45 and is urged downward by spring 62. The piston rod 45 is reciprocated by a crank 65 and on upward movement of the piston rod a driver disc 53 on the piston rod raises the piston body 48 and liquid flows from a reservoir chamber 35 through ducts 58 and 52 to the cylinders 44 and 43. On downward movement of the piston rod 45 the sealing edge 71 of the control cylinder 60 engages the top of the piston body 48 which then begins to move downwards and the liquid thus entrained in the cylinder 44 passes through ducts 58 and 52 to the cylinder 43 and the liquid in this cylinder is pumped past packing 56, acting as a non-return valve to the pressure chamber 59, which causes the piston 40 and the inner prop cylinder 36 to rise. When the head 41 of the prop engages the roof the pressure in pressure chamber 59 will rise and the control cylinder 60, containing liquid from the pressure chamber 59 through the hollow piston rod 45 and ducts 63, will move upwards against spring 62 so that the sealing edge 71 is higher than the bottom 55 of a thickened portion 46 of the piston rod. On downward movement of the piston rod the portion 46 moves the piston body 48 and seals the duct 52 from the chamber 35 so that liquid in cylinder 43 is pumped to the pressure chamber 59, but since the sealing edge 71 does not contact the body 48 liquid in the cylinder 44 passes freely back to the chamber 35 and the piston 49 is therefore ineffective. In the intermediate case where the edge 71 is just above the bottom of portion 46 the edge acts as a throttle valve, part of the liquid in the cylinder 44 passing back to the chamber 35 while the remainder passes to the cylinder 43 past packing 54 acting as a non-return valve. In a modification the control cylinder 60 is formed as an inverted cup shape member whose open end is closed by a thickened portion of the piston rod, the cup shaped member and thickened portion each carrying sealing rings to close the ducts 58 and 52 from the chamber 35. The pressure chamber 59 is provided with a relief valve 68 which can also be raised by a crank 69 to return the liquid in the pressure chamber 59 to the chamber 35 to lower the pit prop. Specification 780,345 is referred to.