GB1144055A - Slide valves - Google Patents

Abstract

1,144,055. Valves. DOWTY HYDRAULIC UNITS Ltd. 7 July, 1966 [4 June, 1965], No. 23972/65. Heading F2V. [Also in Division G3] A spool valve 15 is biased to the neutral position shown by a spring 27 and in this position connects an inlet (29) to an exhaust port 40 via chamber (30) of a similar parallel spool valve (16), check valve (37) and chamber 41. When spool 15 is moved to the left by lever 17, land 25 stops communication between chamber 41 and port 40 and connects passage 39, which also communicates with the inlet, with chamber 48 leading to one side of a jack 51. Fluid from the other side of the jack is expelled to exhaust port 40 via line 68, check valve 67 (which is opened by cam 65 on the spool), chamber 51 and passage 45. Rightward movement of the spool from the neutral position connects the left-hand side of the jack to passage 39 via chamber 51 and check valve 67 and connects the right-hand side of the jack to exhaust via chamber 48 and passage 46. Each spool 15, 16 has a separate operating lever 17 and grooves 53, 54 which co-operate with a respective spring-pressed detent ball 61 to hold the spool in its work positions. Radial passages 72, 73 in the lands 24, 25 communicate with axial passage 70 in the spool, the end of the latter normally being closed by a relief valve 71. If, when the spool is in one of its work positions, the pressure supplied to the jack exceeds a predetermined value, then the relief valve is unseated and allows fluid pressure to act on one or the other of the seats for spring 27 to cause the spool to be returned to its neutral position. The spool may be replaced by a valve of rectangular cross-section having an elongated slot which at all times is open to a pressure supply port, this slot being capable of connecting the supply to either of the work ports whilst the end edge portions of the valve control exhaust of fluid from the unpressurized work port. The detent means may be withdrawable from the indents automatically under fluid pressure when the pressure in the work ports exceeds a predetermined value.