The invention relates to pressure differential indicating apparatus in a hydraulic measuring bridge which includes a measuring chamber that is provided with a valve means that emits a throughflow quantity into the chamber to be measured thereby and a further valve element for discharging the throughflow quantity from said chamber. The measuring chamber is associated with a pressure differential sensor having a movable wall which controls the volume of the measuring chamber and is acted upon by the pressure of a measuring medium that pulsates at slightly different pressures. Further, the pressure differential sensor is provided with a signal transmitter for controlling the measuring chamber volume and includes a cylinder having a wall provided with a piston means associated with a piston rod. The piston rod has one free end thereof arranged to cooperate with the signal transmitter and the piston means further includes a sealing means having an extent which cooperates with the cylinder wall to form an annular seal therebetween.