Abstract: A system comprising a secondary mover such as an hydraulic pump driven by a prime mover such as a motor powered, in use, by an alternating current (AC) electrical supply, whereby the operation of the secondary mover is affected by any frequency variation in a substantially constant voltage AC supply. The system further comprises adjustment means in use powered by the same AC supply as the prime mover, having inherently substantially the same operating characteristics as the prime mover, being coupled to the secondary mover and operable to adjust the operating range thereof in accordance with variations in the frequency of the AC supply.

Abstract: A rotary, variable-displacement hydraulic pump (1) in use driven by a prime mover (4), the pump (1) comprising control means (5) for varying the displacement of the pump and means (17) responsive to a signal related to the rotational speed of the pump and operable to override the control means so as, in use, to prevent stalling of the prime mover (4) within a predetermined operational range of the prime mover.

Abstract: A flow sensor comprises a body (4) formed with a through bore (5), at least one fluid inlet (6, 7) and one fluid outlet (7,6) for permitting ingress and egress of fluid to and from the sensor, and a spool (8) slidably mounted within the bore and having at least one shaped end (38) past which fluid flows from the inlet to the outlet, characterized in that the spool (8) also has resilient means (26) mounted internally thereof and acting against and between two spaced abutments (27, 28) which are connected to the interior of the spool in such a way that they move with the spool in one direction of movement thereof and slide relative to the spool in the opposite direction of movement thereof, the spool being arranged to close the outlet in the null position of the spool when no fluid takes place, and being movable against the action of the resilient means when fluid flow is present, to open the outlet, the extent of movement being representative of the rate of flow of the fluid and being sensed by sensor means (3