Operation with Spring Pressure and
Self-Contained Temperature Pilots
Operation with Air Pressure and Pneumatic
Operation with a Combination of Spring
Pressure and Self-Contained Temperature Pilots:
When a spring pressure pilot is installed in series with a self-contained temperature
pilot, the pilots perform their functions separately and concurrently. Each pilot
regulation cycle is exactly the same as if used alone. When both pilots are open, the main
valve will open. If either pilot closes, the main valve will close. The pressure pilot
acts to limit the maximum downstream pressure as the temperature pilot cycles to control
A solenoid pilot and aquastat may be added as a temperature safety override control.
Benefits of a Combination of Spring Pressure and Self-Contained Temperature
- A single main valve and pilot combination accomplish pressure reduction and temperature
- Self-contained system. No external power source required.
- Thermostatic bulb in sensed fluid guards against over temperature.
- For economical operation, main valve modulates to maintain set temperature.
- Controlling maximum pressure in the steam system limits the condensate temperature from
steam traps to reduce flash steam loss.
Operation with Combination of Air Pressure and Pneumatic
Pneumatic temperature control pilots may used in conjunction with air pressure control
pilots to control temperatures in systems with rapid changes in the required heat load. An
air-pressure-regulating valve is used to limit the pressure of the air supplied to the
pneumatic temperature pilot. Limiting this air supply pressure limits the air pilot
loading force and hence the steam pressure downstream from the main valve.
Combination of Air-Pressure and
Pneumatic Temperature Control
Steam flows to the main valve only when both the pneumatic temperature and the air
pilots are open. Steam flows through the air pilot seat and signal line producing steam
pressure on the main valve diaphragm. The force from the steam pressure pushes against the
main valve spring to control the main valve position. Variations in temperature are sensed
by the temperature sensor, which acts to control the air signal to the air pilot. The air
pilot in turn controls the position of the main valve, ensuring a constant temperature of
the heated fluid or gas.
A solenoid pilot may be added as a temperature safety override control.
Benefits of a Combination of Air Pressure and Pneumatic Temperature Pilots:
- Fast-acting temperature control for rapidly changing loads.
- Provides operator advantage of shutting system down simply by stopping inlet air signal
to air pilot.
- Pneumatic temperature pilots can be remotely located, long distances from main valve.
- Wide, adjustable temperature range.