Fluid control systems

Claim 1

In a control system of the type described comprising a constant displacement variable speed pump with an inlet and an outlet, a relief device including a relief valve having a regulating chamber, a choke, means for directing a portion of said flow from said outlet to said choke and another portion of said flow from said outlet to said relief device, said relief device serving to divide the flow from the pump in accordance with the speed of the latter into a relief flow through said relief device and a controlled power flow through said choke, the relief flow being returned to the inlet of the pump, the improvement comprising a tapping duct connected downstream of said choke to remove fluid from the controlled power flow and pass it to the regulating chamber of the relief device thereby influencing the regulation characteristic, said relief device including means for combining fluid from said regulating chamber directly with the fluid passing with the relief flow, said relief valve being arranged to open and close said last named means, part of the relief valve controlling the abstraction of fluid from the controlled flow comprising a valve piston with longitudinally extending peripheral passages which cooperate with a portion of the bore receiving the piston providing communication between the relief flow and the regulating chamber.