Fema-VNM111-Druckschalter

A pressure switch confirms that pressure or airflow in a burner system is within the required operating band. If the switch does not close or open at the set point, the burner control prevents the ignition sequence from starting or initiates a safety lockout. In forced-draught burners, an air pressure switch proves that the fan is delivering sufficient combustion air during the pre-purge and running periods. Gas pressure switches monitor minimum and maximum gas pressure upstream of the gas valve; a drop below the minimum or a rise above the maximum cuts the fuel supply. All such switches are connected to the burner control via two normally open or normally closed contacts and are selected by the medium (air or natural gas / LPG), the switching range and differential, the connection type (threaded or hose spigot), the electrical rating, and the applicable approval class. The Fema VNM111 is a pressure switch from that category. It is listed under catalogue article 444.676.040 and manufacturer code VNM111. When replacing a pressure switch in a burner or boiler, the most common failure modes are a torn diaphragm, a blocked or leaking impulse tube, or a drifted set point. These faults typically cause a lockout that appears to be an ignition problem. Before swapping the switch, check the impulse line for obstructions and verify that the existing range and differential match the application. Always use a manometer to set the new switch to the correct cut-in and cut-out values as specified by the burner manufacturer.