Model AR 2004 Control Relay

   A relay is a pneumstic amplifier. Like its electronic counterpart, the function of the relay is to convert a small change in the input signal (an air pressure signal) to a large change in the output sgnal. Typically a 0.1 kg/cm² (1 psi) change in the input will produce approximately a 1.2 kg/cm² (12 psi) change in the output.

Principle of Operation

   The air supply enters the relay throuth a port on the surface of the instrument on which the relay is mounted. The input signal (nozzle pressure) enters the relay throuth another port and acts on the diaphragm. Since the diaphragm is in contact with a stem value, the two move in unison.

   As the input signal increases, the stem pushes against a ball value which in turn moves a flat spring, allowing the supply air to enter the relay body. Further motion of the stem value, causes it to close off the exhaust port. Thus when the input pressure increases, the stem (exhaust) value closes and the supply value opens; When the input decreases, the stem value opens and the supply value closes. This varies the pressure to the output.

Servicing Exploded view

Note: If adjustment of tension screw is changed, relay must be recalibrated.