This invention relates to a pressure reducing valve essentially consisting of a cylinder, a control piston movable in said cylinder,Balance Valves one end of said piston being situated in a control chamber and the other in a spring chamber housing a compression spring biasing the control piston in the opening direction; an oil supply chamber in the wall of said cylinder,Reducing Valves said oil supply chamber having a connection for a supply pressure line, and together with a control edge provided on the control piston constituting a variable restriction; an oil discharge line disposed downstream of said restriction for the discharge of oil under a reduced pressure; a load pressure pilot line connected to said spring chamber;BUTTERFLY VALVES and a feedback line connecting said control chamber to said oil discharge line. Such pressure reducing valves are often used in hydraulic control systems for adjusting, and maintaining the supply pressure from a pump or source of pressure, subject to large variations, at the correct reduced pressure. It has been found that pressure reducing valves known from practice are not capable of effecting a reduced pressure of constant level independently of variations in the supply pressure. Major deviations are caused by flow forces occurring within the pressure reducing valve, which with increasing supply pressure push the movable control piston of the pressure reducing valve further to its closed position than is necessary to effect a reduced pressure of the desired level. It is an object of the present invention to overcome this drawback and to provide a pressure reducing valve with which the desired reduced pressure can be kept virtually constant irrespective of substantial variations in supply pressure. The invention is based upon the insight that such oil streams must be supplied to the control piston of the pressure reducing valve that the control piston occupies a stable position, that is to say, that the oil stream to the control chamber is equal to an oil stream from the control chamber when the reduced pressure has reached the desired level, independently of the spurious forces exerted on the control piston. These oil streams to and from the control chamber can be so controlled, independently of the flow effects occurring in the pressure reducing valve that the stable position occupied by the control piston is adapted to the flow effects occurring within the pressure reducing valve. For this purpose the pressure reducing valve according to the invention is characterized in that said feedback line is provided with a fixed restriction, and the control chamber is connected through a conduit to the spring chamber, in which conduit a pressure-dependent restriction is provided, said control piston occupying a stable position if the rate of flow through the fixed restriction equals the rate of flow through the pressuredependent restriction. Preferably, the pressure-dependent restriction is a vanecontrolled nozzle system, the vane of which is constituted by a membrane forming a partition between, on the one hand, an auxiliary control chamber connected to the control chamber, and on the other hand, a load pressure chamber connected to the spring chamber, in which load pressure chamber the nozzle is arranged.

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