Proportional valve

A proportional valve (1) with a pilot valve (2) that can be activated by a control signal and a booster valve (3) that can be actuated by means of the pilot valve (2), wherein the proportional valve (1) has a compressed-air port (6) for connection of a compressed-air supply, a working port (5) and a vent port (4),

• wherein the booster valve (3) has three valve elements (8, 9, 10) connected in series and respectively movable in an axial direction against a spring force, namely
• a first valve element (8) actuated by the pilot valve (2),
• a second valve element (9), which is actuated by the first valve element (2), and
• a third valve element (10), which is actuated by the second valve element (9),
• wherein, in a basic position of the proportional valve (1), the first, the second and the third valve elements (8, 9, 10) are spaced apart from one another in pairs and, within the booster valve (3), a first sealing seat (26) acting between the first valve element (8) and the second valve element (9) and a second sealing seat (27) acting between the third valve element (10) and the housing (16) are formed and disposed in such a way that during variation of the control signal that activates the pilot valve (2) and of the resulting cascade-like positioning of the axial positions of the first, second and third valve elements (8, 9, 10), various switched states can be set for venting of and air admission to the working port (5) and for holding a pressure present at the working port (5),
• wherein further a position sensor (31) is provided to detect the axial position of the first valve element (8) and a control unit (36) of the proportional valve (1) is set up in such a way that the measured signal of the position sensor (31) is evaluated for calculation of the control signal for the pilot valve (2), needed in order to achieve a desired switched state of the booster valve (3).