Patent GB-845866-A (GB)
Title: Improvements in or relating to relief valves for fluid pumps for example as used in hydraulic variable pitch propeller control apparatus
Inventor: WALL RICHARD JAMES
IPC: F16K17/06
Filed: 1955-11-09
Abstract: 845,866. Relief valves; fluid-pressure servomotor control-systems. ROTOL Ltd. Oct. 26, 1956 [Nov. 9, 1955], No. 32089/55. Class 135. A fluid pump relief valve 60 comprises a closuremember 77 loaded by resilient means and a doubleacting fluid motor 100 for varying the loading of the resilient means and hence the pressure at which the closure-member will open. The closure member 77 is of tubular form and incorporates radial ports 78 of rectangular configuration with the sides thereof inclined to the axis of the member 77 to ensure a smooth opening movement; a disc 90 is urged against a seat 91 on the inner end of the closure-member 77 by a spring 92, the other end of which abuts a disc 93 that seats on a stop 95 in the casing. The disc 93 abuts a rod 75 which extends into the cylinder of a double-acting piston 74 and abuts said piston. The chambers on either side of said piston are connected by lines 80, 84 to conduits 24, 25 which lead to a propeller pitch change motor 18 supplied with fluid from a pump 54 under the control of a governor valve 32 as described later. The pump delivery pressure acts in the outer end of the casing 76 via a conduit 57 and upon exceeding the pressure setting of the spring 92 the ports 78 open to a space 101 and connect the conduit 57 with a conduit 61 which leads to the pump inlet, the disc 90 provides an emergency valve that opens should the valve member 77 become jammed in the casing. The loading of the spring 92 is determined by the position of the piston 74 which is movable between two positions in accordance with which conduit 24, 25 is receiving fluid from the pump 54. The governor valve 32 is in a housing 31 and has two lands 33, 34 and a central bore 35 that interconnects lower and upper chambers 36 and 40 through ports 137 whilst a rotatable sleeve with three sets of radial ports 37, 38 and 39 co-operates with the valve 32, the radial ports registering with annular grooves 41, 42 and 43 respectively in the casing; in the equilibrium position shown, lands 33 and 34 close ports 37 and 39. The valve 32 is lifted or lowered for coarse or fine pitch operation respectively in accordance with the position of flyweights 48 pivoted on the engine-driven sleeve 136; the loading of the governor spring 52 is adjusted to vary the datum setting. The pump 54 supplies fluid to an annular space 63 between the lands 33, 34 via the groove 42, whereupon any movement of the valve 32 places the space 63 into communication with either conduit 24 or 25 by way of grooves 41 or 43, the other conduit 25 or 24 being connected to the pump intake through a conduit 62, chamber 40 and/or chamber 36. The piston 17 is thereby moved to the right or left to adjust the aeronautical propeller blades 12 in a coarse or fine pitch direction. The relief valve 60 ensures as described above, that the pump provides a higher pressure for movement of the piston 17 in the coarse pitch direction than in the fine pitch direction.