Apparatus for controlling a fluid medium

An apparatus for the control of a fluid medium, comprising a double-acting reciprocating piston, a cylinder for housing said piston, a switching element actuated by a pressurized fluid medium, pressure source means for supplying pressurized fluid medium to the switching element, a pair of actuation elements working in opposed relationship to one another, said switching element being reversible between two switching positions by means of said two actuation elements, an actuation line provided for each actuation element for connecting the pressure source with each such actuation element, a respective normally closed shutoff valve having an inlet side and an outlet side for admitting pressurized fluid from the pressurized source means to the actuation line of each actuation element, said shutoff valves having only two positions defining an open position communicating said inlet and outlet sides and a normally closed position blocking flow between said inlet and outlet sides, means normally closing the shutoff valves, a respective throttle means provided for each actuation element and shutoff valve and connected with the outlet side of its associated shutoff valve for increasing the pressure in the actuation line to thereby operate its associated actuation element, each said actuation element being directly connected to its associated actuation line between the outlet side of its associated shutoff valve and its associated throttle means, the inlet side of each shutoff valve being directly connected to the pressure source, said shutoff valves being arranged respectively at the region of the end positions of the stroke of the reciprocating piston, each shutoff valve having a respective plunger laterally extending into the cylinder and cooperating with a control surface of said reciprocating piston for operating said shutoff valve.