Abstract: A fluid flow device for minimizing the effects of fluctuating pressures on the fluid flow rate has a variable restriction in the fluid path through the device arranged to produce a lesser restriction as the pressure difference between the inlet and outlet of the device increases, and vice versa. This first, variable restriction is formed by an inlet tube and a blocking member. A second, constant restriction for the fluid flow is formed by the tube and a parallel bore through which the tube extends, to produce a pressure drop which creates a pressure differential across a diaphragm balanced by a spring. A change of the pressure differential across the device also changes the pressure differential on the diaphragm, which is connected to the blocking member, so that movement of the diaphragm has the effect of varying the restriction in the manner described to reduce flow rate variations through the device.

Abstract: A fluid-operated actuator (2) is connected to a pumping unit (12) through a control unit (10) in which are mounted control valves (30,32) for regulating the movements of the actuator. The control valves communicate with the actuator and the pumping unit through conduits in replaceable adaptor plates (60a,60b,60c). By changing the adaptor plates, different operating modes of the actuator can be selected. The pumping unit is carried on the control unit through a rotationally adjustable connection to permit it to be mounted upright although the orientation of the actuator and control unit may vary.