Abstract: A device for preventing the back flow of water from a point of use into a water supply line. The device includes a unitary casing having an inlet, a central chamber, an outlet, a removal port and a drain vent opening. The inlet, the central chamber and the outlet are coaxially aligned. A relief valve is located in the central chamber and offset from the coaxial alignment of the inlet, the central chamber and the outlet. There is a cover for the removal port. There is also a pair of check valves. One is mounted between the inlet and the central chamber and the other is mounted between the outlet and the central chamber. The device allows water to pass unobstructed in a straight-through flow path through the device. The back flow of water is prevented.

Abstract: A back flow preventing device is disclosed which prevents the reverse flow of water from a point of use into a water supply system. The device has a casing with coaxially aligned inlet and outlet openings, and containing coaxially aligned inlet and outlet check valves. The coaxial alignment of the inlet and outlet openings, and of the inlet and outlet check valves serves to minimize the pressure drop through the device. Between the inlet and outlet check valves is a diaphragm actuated relief valve which opens to drain the passage between the check valves if they should malfunction or if there is a drop in the supply line pressure sufficient to cause actual or potential reverse flow back toward the supply line. The internally-located inlet and outlet check valves are each removably secured in place by internally-located retaining rings.

Abstract: A back flow preventing device which prevents the reverse flow of water from a point of use into a water supply system. The device has a casting with coaxially aligned inlet and outlet openings, and containing coaxially aligned inlet and outlet check valves. The coaxial alignment of the inlet and outlet openings, and of the inlet and outlet check valves serves to minimize the pressure drop through the device. Between the inlet and outlet check valves is a diaphragm actuated relief valve which opens to drain the passage between the check valves if they should malfunction or if there is a drop in the supply line pressure sufficient to cause actual or potential reverse flow back toward the supply line.

Abstract: A back flow preventer for preventing contamination of a water supply. The preventer includes check valves which are enclosed in a casing comprised of a body and a single removable cover. The check valves are vertically disposed and spaced laterally from each other. The valves may be removed for servicing when the cover is removed without disturbing other parts of the device. Between the check valves is a relief valve which opens to drain the passage between the check valves when there is a drop in the supply line pressure sufficient to cause actual or potential reverse flow back toward the supply line. The check valves open by movement in opposite directions. Each check valve unit includes a tubular strainer through which all water must pass. The check valve units, while identically dimensioned as to the valve structure, include other parts of unequal dimensions which preclude accidental reversal of the units when being initially assembled or replaced after servicing.