GB1254841A - Improvements in or relating to fluid pressure operated motors - Google Patents

Abstract

1,254,841. Reciprocating motors; compressed gas engines. BUTTERWORTH HYDRAULIC DEVELOPMENTS Ltd. Dec. 4, 1968 [Sept. 8, 1967], No. 41082/67. Headings F1A and F1M. In a fluid-pressure operated motor of the type in which reciprocation of a differential pressure biased piston 17 is controlled by reciprocation of a differential pressure biased spool 16 itself controlled by movement of the piston, the arrangement is such that the volume of fluid input equals the volume output, whereby intermittent exhaust back pressure is avoided. In the embodiment illustrated, a land 16d of the spool 16 controls a port 5a so that, when the piston 17 moves against its bias, i. e. in the direction of arrow Y, the volume of fluid displaced from the constant pressure piston chamber 13 passes through passages 4, 5 to the alternating pressure piston chamber 12, Fig. 1, and, provided the crosssections A2, A3 of piston lands 17b, 17c are such that A2 is greater than A3, which is greater than A1, the piston rod cross-section, the volume of fluid exhausted from a variable volume chamber 14 equals the volume entering the alternating pressure piston chamber 12 from the input. When the piston 17 moves in the direction of its bias, Fig. 3 (not shown), the excess of fluid displaced from the alternating pressure piston chamber 12 over that passing into the constant pressure piston chamber 13 passes to the variable volume chamber 14, the rest of the fluid passing to the exhaust.