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2. Backflow prevention device - Wikipedia

   en.wikipedia.org/wiki/Backflow_prevention_device

   Backflow means the undesirable reversal of flow of a liquid, gas, or suspended solid into the potable water supply; a backflow preventer is designed to keep this from happening. Points at which a potable water system connects with a non-potable water system are called cross connections .

3. Reduced pressure zone device - Wikipedia

   en.wikipedia.org/wiki/Reduced_pressure_zone_device

   A reduced pressure zone device (RPZD, RPZ, or RPZ valve) is a type of backflow prevention device used to protect water supplies from contamination. RPZDs may also be known as reduced pressure principle (RP), reduced pressure principle backflow prevention devices, [1] [2] reduced pressure zone assemblies (RPZA), [3] or reduced pressure principle ...

4. Double check valve - Wikipedia

   en.wikipedia.org/wiki/Double_check_valve

   A double check valve or double check assembly (DCA) is a backflow prevention device designed to protect water supplies from contamination. [1] It is different from the two-way check valves (sometimes erroneously referred to as double check valves) used in air brake systems on heavy trucks which select from the highest pressure source.

5. Atmospheric vacuum breaker - Wikipedia

   en.wikipedia.org/wiki/Atmospheric_vacuum_breaker

   It is usually constructed of brass and resembles a 90-degree elbow with a hood on its top to allow air to enter the water system if a siphon attempts to form. Inside this elbow is a poppet valve that is held "up" by the water pressure found in the system, closing the air entrance to the device. If the pressure in the "upstream side" is reduced ...

6. Backflow - Wikipedia

   en.wikipedia.org/wiki/Backflow

   Backflow occurs for one of two reasons, either back pressure or back siphonage. [1] Back pressure is the result of a higher pressure in the system than in its supply, i.e. the system pressure has been increased by some means. This may occur in unvented heating systems, where thermal expansion increases the pressure.

7. Vacuum breaker - Wikipedia

   en.wikipedia.org/wiki/Vacuum_breaker

   The devices allow air into the system to prevent a siphon at the point of use. Hose connection vacuum breakers are installed on faucets and hose bibbs to prevent backflow into the water supply. Pressure type vacuum breakers are similar to atmospheric vacuum breakers but have a spring-loaded check valve to allow operation of under pressure for ...