The Model RFS-4001-025 and Model RFS-4001-031 Differential Pressure Switches are general purpose, airflow-proving switches designed for HVAC and building automation applications. These switches may be used to sense positive, negative, or differential air pressure. The plated housing contains a diaphragm, calibration spring and snap-acting switch. The Model RFS-4001-025 pressure connections located on each side of the diaphragm, accept copper or flexible 1/4 in OD tubing. The Model RFS-4001-031 has tri-barb connectors that accept 1/8 in, 1/4 in and 5/16 in ID flexible tubing. An enclosure cover guards against accidental contact with the live-switch terminal screws and the set point-adjusting screw. The enclosure will accept a 1/2 in conduit connection.