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Backflow prevention device. The simplest, most reliable way to provide backflow prevention is to provide an air gap.An air gap is simply an open vertical space between any device that connects to a plumbing system (like a valve or faucet) and any place where contaminated water can collect or pool.
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 ...
A perforated disc (4) covered by a flexible plate or flap (5) is joined by the siphon rod (6) to the flush lever. Pressing the lever raises the plate, forces water over the top of the siphon into the vertical pipe, and starts the siphonic discharge. Water flows past the flap until the cistern is empty, air enters the siphon and the flush stops.
A vacuum breaker is a device that prevents water from being siphoned backward in a direction it is not desired to go. They are commonly placed on a bibcock valve or toilet or urinal flush valve, in which application they can prevent hose or drainage water from back-siphoning into the public drinking water system.
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An anti-siphon valve is also required here to prevent pressure drops in the water supply line from suctioning water out of the toilet tank (which may contain additives such as "toilet blue" [53]) and contaminating the water system. Anti-siphon valves function as a one-direction check valve. Anti-siphon valves are also used medically.
Sometimes called a check valve or a backflow preventer, a chemigation valve is an apparatus designed to protect water supplies from agricultural chemicals used during chemigation, the application of chemicals such as fertilizers and pesticides through irrigation water. [1]
Toward the end of the discharge process, the ballcock responds to the drop in water level and refills the tank. Should the float or valve fail and allow the water level to exceed the fill line, the water will pour into the overflow tube and out to the bowl (in the flapper valve type) or to an outside drain (in the siphon type).