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Discuss Honeywell EA122 automatic bleed valve in the Plumbing Forum | Plumbing Advice area at



Am going to fit an automatic bleed valve to replace the knackered manual one. Reading the Honeywell blurb it says it should be fitted on the positive side. Is there any reason for this? and could I not fit it on the negative side?


Gas Engineer
possibly it uses a float system so air could be sucked in

as i thought
The AAV is a very simple and effective device, comprising a float inside a chamber. In the Honeywell EA122 (illustrated) water fills the chamber during normal operation, holding the float up to seal the vent at the top. If air enters the chamber, the float drops as the water level falls, allowing the air to escape through the vent. The float then rises again to re-seal the vent. This is repeated whenever air enters the AAV.

The vacuum break on the bottom of the EA122 prevents an air lock forming and encourages air to be released from water. When choosing a position for installation, pick an accessible area which can be seen and serviced easily, and in a point in the system where air is likely to collect. On a horizontal pipe run, provide a short upstand to ensure the air break is not in the water flow.

It should always be installed in the positive pump pressure side of the system, where air is likely to be trapped, as it is possible air will be drawn in under negative pressure. A good static head is important: the greater the head, the more positively the valve will close.

An AAV situated on a bend at the top of a vertical run works well on a gravity system but not on a pumped system. This is because the fast-moving air follows a route around the bend similar to that of a racing car and so bypasses the AAV. Air is removed most efficiently when the AAV is positioned at least 150mm from a bend.


Well both my options are not over 150mm so will have to make do until later in the year when I rejig the whole thing.

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