A pressure responsive control device, particularly for controlling the operation of a pump to maintain the pressure level of a fluid in a reservoir within a predetermined pressure range, comprising a sensor which compares said pressure level with a reference pressure (atmospheric air) and a switch which is actuated by said sensor as a function of the difference between said pressures and which itself controls the operation of the pump.
According to this invention, the force exerted by the pressure difference on a first movable wall (38, 48) which closes a first chamber (30) in the sensor (18) is opposed by a lesser force exerted by same pressure difference on a second movable wall (52, 58) which separates said first chamber (30) from a second chamber (32) which itself is connectable either to the reference pressure or to the first chamber as a result of the displacement of said walls, thus providing for snap actuation of the associated switch (16).
For use particularly in controlling operation of vacuum pumps in automotive vehicles.