Prevents dangerous back-siphonage; automatically self-drains when all attachments are removed completely from the valve's outlet. Protects the valve and faucet from freezing and rupturing in cold weather. Constructed with brass body and adapter. Buna O-ring and seat disc, steel set screw, stainless steel springs and the highest quality molded parts. NOTE: THESE UNITS ARE NOT INTENDED FOR USE WHERE WATER CONTAMINATION COULD OCCUR AS A RESULT OF DRAINING OR FOR PERMANENT CONTINUOUS PRESSURE INSTALLATION. FOR CONTINUOUS PRESSURE SYSTEMS, INSTALL THE BFP DESCRIBED HERE.