Instruction Manual
D200126X012
2502 Controllers
June 2017
19
4. Slowly open the downstream and upstream manual control valves in the pipeline and close the manual bypass valve
if one is used.
5. With the controller set at the desired control point, narrow the proportional band until a cycling condition exists.
Then broaden the proportional band slightly until stable control is obtained.
6. Adjust the reset control to obtain the highest reset setting without introducing cycling.
7. To ensure that the optimum proportional band and reset settings have been obtained, momentarily create a load
upset. If cycling occurs, broaden the proportional band slightly and repeat the load upset until stability is attained.
In general, the narrowest proportional band and the highest reset setting that will not produce cycling will provide
the best control.
Principle of Operation
All 2502 controllers use the same basic pressure‐balanced relay with a yoked double‐diaphragm assembly (figure 10).
This relay is connected so that supply pressure is fed to the inlet side of the relay valve and to the fixed restriction.
From this restriction, the air pressure goes into the relay chamber on the side of the large diaphragm, and to the
nozzle. As long as there is no pressure change on either diaphragm, the relay valve remains in equilibrium with both
the inlet and exhaust ends closed.
