Pneumatic Relay

one of the main elements of pneumatic automatic control; a control element in which the sensing member is a diaphragm (usually elastic) or bellows, and the me-chanopneumatic converter of the mechanical displacement into a change in pressure of air or a gas is a nozzle and baffle.

Both single diaphragms and sets of diaphragms (diaphragm blocks) are used in diaphragm pneumatic relays, which are the most common. The faces of the diaphragms function as baffles for one or two nozzles, which are located along the axis of the diaphragm. The operation of a diaphragm pneumatic relay may be analog (continuous) or discrete (digital).