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A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure (normal check-valve behavior), it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.
A check valve is a basic form of backflow prevention, but often more complex devices are required because check valves are not considered to be reliable, when compared to more sophisticated devices with redundancies and reduced-pressure zones. [further explanation needed]
A recent introduction to the UK has been the Reduced Pressure Zone (RPZ) valve, a form of double check valve where the intervening zone is drained and normally kept empty. [1] If the downstream valve leaks and permits backflow, this will drain out through the vent rather than building up pressure against the upstream 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. It ...
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 ...
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 to atmospheric pressure or below, the poppet valve drops and allows air to enter the system, breaking the siphon. [1]
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