Pressure Switch
The watchdog of system limits. Pressure switches monitor gas, air, and oil pressures to ensure they remain within the safe operating range, triggering a shutdown if limits are exceeded.
How It Works
A pressure switch is a simple electromechanical device. It uses a sensing element (usually a diaphragm or bellows) that pushes against a calibrated spring.
When the process pressure overcomes the spring force, it snaps a microswitch. This switch is wired into the burner's safety interlock circuit (limit chain). If the circuit opens, the burner performs a safety shutdown.
Common Applications
Air Pressure Switch
Function: Proves that the combustion air blower is running.
Setting: Typically set slightly below the minimum air pressure required for safe combustion.
Low Gas Pressure Switch (Min Gas)
Function: Ensures sufficient gas supply pressure.
Setting: Typically 50% of the nominal inlet pressure. Prevents the burner from running lean or losing flame stability.
High Gas Pressure Switch (Max Gas)
Function: Detects regulator failure or pressure spikes.
Setting: Typically 150% of nominal pressure. Prevents over-firing and dangerous rich conditions.
Technical Details
Adjustability
Most switches feature a dial for setting the switching point. Some have a secondary dial for adjusting the switching differential (hysteresis).
Test Point
Many modern switches (like Dungs GW) include a built-in test nipple to easily connect a manometer for calibration.
Leading Manufacturers
- DungsGW series
- KromschroderDG series
- HoneywellC6097, C6045
- AntunesModel A, Model G
- SiemensQPL series
Related Components
Did you know?
Air pressure switches are often "differential" switches. They measure the difference between the blower pressure and the combustion chamber back-pressure to ensure true airflow, not just static pressure.