Central Heating Component ID?

Hi,
Right all you knowledgeable persons. I moved house and am trying to get to know the various bits & pieces. What is the arrowed component in the following picture
http://www.btinternet.com/~nigel.percy/heating.jpg
What's it for? How does it work?
Cheers
Nige
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Looks like an automatic bleed valve to me (lets air out of the system)
-- Tony Collins

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It has a float in it which drops when air fills the bottle, opening up the valve, and letting air out.
-- Tony Collins

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On Thu, 3 Jul 2003 21:23:58 +0000 (UTC), "Nigel Percy"

It's an automatic air vent. There is a high point in the pipework where it's fitted which would otherwise accumulate air.
Inside the brass chamber, there is a little plastic float, normally with a lever with a rubber disc on the end. The disc covers a hole in the top of the chamber, which in this case has a second cover on the outside - the red cap. Air will tend to go up the vertical pipe and to the chamber and the float will drop, opening the hole. Thus the air escapes, water rises as does the float and the hole is closed.
These valves are not always perfect in sealing, so the red cap is there as a means to prevent escape of water that is not known about. You can check if there is accumulated air by turning the red cap anticlockwise. You may get a few drops of water as the valve closes if there is accumulated air.
.andy
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Looks like an automatic bleed valve to me - it has a float chamber inside
--
geoff

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writes

to
How effective are these ? I've got one fitted but a small amount of air still manages to collect in the bathroom radiator every couple of months during winter.
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wrote:

They are reasonably, but can tend to weep after a while. Fixing involves taking them apart and cleaning. On the better quality ones like the Honeywell you can rotate the base and isolate the chamber - then the top can be taken off for cleaning. On some of the cheaper ones there is an auxilliary valve in the bottom which closes as the chamber is removed. I 've had some of the Honeywell ones for over a year and they have been OK so far and not seeped water. However, I don't expect there to be much accumulated air either.
In any case this isn't necessarily going to help much with your radiator problem, since the AAV will only trap passing air to where it is fitted.
Have you checked that this is not hydrogen from your radiator? If it is then you have a corrosion problem.
.andy
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