Honeywell Pressure control L91B1050/U

The Honeywell L91B1050/U is a pressure switch designed for use with steam, air, non-combustible gases, or liquids that do not corrode brass or bronze bellows. It features a sensing element made of brass or bronze bellows and a switching element consisting of one 140 ohm potentiometer. The maximum working pressure is 1551000 kPa. This device monitors pressure within a burner system and sends a signal to the burner control to allow or halt the ignition sequence based on pressure conditions.

When selecting a replacement pressure switch of this type, key parameters include the medium (air or gas), switching range, differential, connection type (thread or hose spigot), contact rating, and approval class. The exact setpoint and differential must match the original to ensure safe operation and prevent nuisance lockouts. Verify the impulse line is clean and mount the switch in the orientation specified by the manufacturer.

Typical failure modes include a torn diaphragm, a blocked impulse tube preventing accurate pressure sensing, or a drifted setpoint due to wear or contamination. These failures often present as repeated lockouts that appear to be ignition problems. After confirming spark and fuel supply are correct, suspect the pressure switch and check its operation.