Abstract: Improvement to electro-fluid relays useable to signal either the maximum or minimum limit of pressure in a fluid system, or the position of a movable part of a jack.The relay is constituted of a pipe fitting (1,2) attached directly onto an apparatus (5) or onto a pipe and including a body presenting a pneumatic control inlet (6) in communication with the said apparatus or the said piping, the said control inlet (6) being linked to a space situated on one side of an elastic membrane (16) submitted to the fluid pressure established in the control inlet (6), the said membrane (16) being linked by a transmission member (18) sliding in the body to a means of control (22) of an electric contactor (23).The invention is utilized for the control of a jack.