Automatic bleeding valve
plumbing valve used to automatically release trapped air from a heating system
An automatic bleeding valve or air release valve (ARV) is a plumbing valve used to automatically release trapped air from a heating system.
Air, or other gas, may collect within plumbing. For water delivery systems to taps and basins, particularly with good main supply pressure, this air is usually flushed through with the water flow and does not cause a problem, although in some hot-water systems (particularly Gravity systems) air locks can be problematic.
In a closed heating system though, it has no other means of escape and builds up. An air bubble trapped within a radiator means that no hot water circulates in the upper part and so the heating power of the radiator is reduced. If air is trapped within the boiler this may cause pump cavitation or boiling and overheating within the heat exchanger.
Installation and use
Automatic valves are used to release trapped air as it collects. They are not a substitute for bleeding a system manually when it is first filled during commissioning, nor for remedial bleeding if the system becomes choked with trapped air. In those cases, individual bleed screws on each radiator, or high pipe run, are opened manually.
The valves are installed at a high point of the system, where trapped air collects.
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