This sketch shows a QB2 electro-pneumatic closed-loop proportional regulator air piloting a steam regulator to control temperature in a bakery proof box. The combination of QB2 and Steam Regulator creates a simple steam control valve.

The QB2 and steam regulator assembly replace traditional steam valves and I to Ps. The Proportion-Air steam regulator assembly allows for tighter control of temperature for two reasons:

1. The steam regulator has a sensor port connected between steam pressure downstream and the bottom of the regulator’s diaphragm so it can “see” downstream pressure and compensate mechanically for it. A steam valve does not have this sense port.

2. The assembly uses a Proportion-Air QB2 which takes feedback from a downstream pressure transducer and closes the loop around pressure for tighter closed-loop control. Since temperature is directly related to the pressure of saturated steam, this assembly will provide tighter control of temperature. No PID loops need to be tuned with this assembly, just give the QB2 the command to go to the desired pressure (temperature) and it will achieve it.