Membrane box 1 is made up of two corrugated membranes a and b, soldered together. The centre of membrane a is stationary and is secured to a pipe member which is to be connected to the space where the pressure is to be measured. The centre of membrane b is linked to the mechanism for operating the gauge hand. When there is a difference in pressure inside and outside the box, movable membrane b bends inward or outward. Motion of the membrane is transmitted by tie-rod 2 to lever 3 of hand d, turning about fixed axis A. Suc a membrane box is used to measure the relative pressure.
$4055$EHP,M$