Abstract: A hydraulic variable-displacement axial piston pump comprising a swash means which tends to move to a de-swashed condition when the pump is working, and a torque limiting device, the torque limiting device comprising a piston and cylinder arrangement having a movable member which when extended acts via the swash means to increase the displacement of the pump, a spool, and a spring which has one end acting on the spool and its other end acting on the movable member thereby placing the spool under a spring load which varies with the extension of the movable member, the spool being coupled to pump delivery pressure at its end remote from the spring and the spool being arranged to control the flow of fluid to the movable member, whereby a limitation on the on-swash condition of the swash means is obtained which is inversely proportional to the pressure at which the hydraulic fluid is discharged from the pump.

Abstract: A pump comprising a casing, a shaft which rotates in the casing when the pump is in use, a seal which is subjected to pump inlet pressure, a flexible ring member positioned between the seal and an inlet for the pump, and a non-flexible ring member positioned between the seal and the flexible ring member, the pump being such that one of the flexible or non-flexible ring members is mounted on the shaft for rotation with the shaft and the other flexible or non-flexible ring member is mounted around the shaft but spaced from the shaft, whereby when the flexible ring member is not flexed pump inlet fluid can pass to the seal and whereby any sudden increase in pump inlet pressure causes the flexible ring member to flex and sealingly engage with the non-flexible ring member to prevent the sudden increase in pump inlet pressure the seal.

Abstract: A hydraulic pumping arrangement for pumping a liquid to a hydraulic system, which comprises pumping means for pumping the liquid, swash means including a variable swash member which enables the liquid output of the pumping means to be infinitely varied between minimum and maximum, a first piston-and-cylinder arrangement for increasing the position of the swash member to increase the liquid output of the pumping means, a second piston-and-cylinder arrangement for decreasing the position of the swash member to decrease the liquid output of the pumping means, control means for controlling the flow of liquid for the second piston-and-cylinder arrangement, switching means operative to pass liquid from the system to the control means at a first condition in the system and operative to stop liquid from the system passing to the control means at a second condition in the system, and valve means for isolating the pumping arrangement from the system and from a main pump normally supplying liquid to the system, the cont