Abstract: A pressure-activated diaphragm valve which when installed in the main up-stream side of a pressurized line, responds to signals from a control unit to shut off the main supply line and at the same time, opens a drain port on the down-stream side of the valve. When used as a freeze protection system, the main water line is shut off and the drain port opened before the freeze point, thereby, eliminating water damage from frozen, broken pipes. The valve also is self-cleaning and has a magnetic plug to remove and keep metallic particles out of the control chamber and the control unit has automatic and manual modes.