Abstract: A regenerative pump is provided in which an impeller is centrally located within a cavity and variable volume side channels are provided such that the pump characteristic can be varied. A control mechanism is provided for controlling the volume of each side channel in a symmetrical manner.

Abstract: A gear pump has a pair of externally meshed gears, and an inlet port and an outlet port on respective sides of the zone of mesh of the gears. The teeth of the gears have their non-working flanks relieved so as to increase an inter-tooth volume lying between two adjacent contact areas of the gears, this inter-tooth volume first decreasing and then increasing as the gears rotate. The relief of the non-working flanks is such that each successive inter-tooth volume communicates with the inlet port before that volume increases from its minimum value.

Abstract: A control valve arrangement for regulating a servo pressure which in turn controls the stroke of a variable displacement pump has a control element positioned by means of an operating pressure derived from the pressure at the pump outlet. A solenoid valve is operable to reduce the operating pressure and thereby to position the control element so as to cause the pump stroke to be reduced. Movement of the control element beyond a predetermined position in a pump stroke reducing direction opens a bypass connection which maintains a small cooling flow through the pump.