Abstract: Apparatus for regulating the output of a system feed with a fluid medium irrespective of the instantaneous pressure in the system comprising a regulating device including an adjustable throttling connected in the inlet line of the system. A preset non-return valve is connected downstream of the throttling and a spring loaded non-return valve is connected in series with the preset non-return valve and is fitted with a leakage connection extending to a reservoir tank. A control line is connected between the pre-set non-return valve and the spring loaded non-return valve and it senses pressure drop at the throttling so that when the pressure drop reaches a predetermined value the non-return valve opens so that fluid medium is transferred and pressure in the control line increases. A central device is connected in the control line for regulating a quantity of flow to the primary line and the control device comprises a spring loaded piston actuated by increased pressure in the control line.