Abstract: A pressure responsive reed switch operating mechanism comprises a magnet mounted on a rod which is fixed to a dashpot piston and which is spring urged against a movable stop. The location of the stop is controlled by a pressure responsive system comprising a fluid pressure servo motor, a buckling link, a lever and a coil spring. The stop is stationary and the magnet displaced from its switch actuating location until the predetermined switching pressure is established whereupon the coil spring yields and the buckling link buckles with a snap action so that the stop is moved rapidly away from the rod. The rod follows the stop slowly, due to the combined action of the dashpot and the spring, until it reabuts the stop whereby the magnet is moved into position to actuate the reed switch a predetermined time interval after establishment of the switching pressure.