Pneumatic
Pressure Transmitter
Model #: 173
This transmitter is designed to measure and indicate a process pressure and to transmit a proportional air pressure to a pneumatic receiver. Pressure applied to the helix tube of the measuring unit results in motion of the pilot stem.
Supply air flows through a restriction into the chamber between the two diaphragms and into the bellows unit and is exhausted past the pilot in the bellows unit. The same supply air is also admitted into the chamber above and below the two diaphragms through the ball-seat valve stem point operates an automatic bleed which allows excess air to escape to the atmosphere through the main diaphragm bleed slots.
Inward motion of the pilot opens the port, decreasing the pressure in the bellows and between the diaphragms. The decreased pressure on the one side of the main (or booster) diphragm opens the bleed port on the other side of this diaphragm assembly, thereby relieving the pressure in the chambers above and below the diaphragms and decreasing the transmitted pressure. The decreased pressure under the bellows unit allows the range spring to reposition the bellows in the new equalibrium position.
Outward motion of the pilot close off the port and increases the pressure in the bellows unit and between the diaphragms. The increased pressure on one side of the booster diaphragm closes off the diaphragm bleed port and open the ball-seat valve, increasing the pressurre in the chambers above and below the diaphragms and the transmitted pressure. The increased pressure under the bellows compresses the spring and the unit assumes a new equalibrium.
