Pressure transmitters

A pressure transmitter consists of a stem (1), head (2) and diaphragm (9). The diaphram bears an obturating member (10) which cooperates with a seating in the stem. The diapragm (9) is mounted slightly away from the head (2) and the pressure transmitter is used with a constant flow system which passes air into the space behind the diaphragm and out through the seating and with a remote reading pressure gauge. The reading of the pressure gauge rises as the pressure urging the diaphragm to close the seating rises. Calibration is achieved by machining shoulder (50) of the stem. In other embodiments the seating is formed on an insert in the bore (15) and to position is adjustable.