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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 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.
Siphon tubes are a basic implement used in irrigation to transfer water over a barrier (such as the bank of a raised irrigation canal), using the siphon principle. At the simplest they consist of a pipe with no working parts. To work they rely on the water level in the canal being at a higher level than the water level in the field being irrigated.
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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.
"Non-slam" check valves can be used to reduce the pressure surge. Filling an empty pipe that has a restriction such as a partially open valve or an orifice that allows air to pass easily as the pipe rapidly fills, but with the pressure increasing once full the water encounters the restriction.
The importance of valve leakage depends on what the valve is controlling. For example, a dripping tap is less significant than a leak from a six-inch pipe carrying high-pressure radioactive steam. In the United States, the American National Standards Institute specifies six different leakage classes, with "leakage" defined in terms of the full ...