How does auto bleed valve work

[jefword]

Hi, I've just replaced one of these types of automatic radiator bleed valves that has been in one of my rental properties and doing it's job for the last eight years. They are the ones that Wickes sell. The old one seemed to be no longer functioning. The new one seems to have solved the problem (well technically the symptom anyway)

I was just intrigued (sad I know) how this type works and is there anything to go wrong inside them. Is it some material inside which swells when wet to give a seal? Also, I wondered if there is a correct technique to set the screw position or is it a trial and error method like the one I used.

I've searched on the net for info but can't find any so I just thought I would ask on here before I grind the old one in half to see (even sadder).

Thanks.

[jefword]

That was fast. Thanks very much.

[jefword]

jefword said:

The new one seems to have solved the problem (well technically the symptom anyway)

I did actually infer it masked the fault by curing the symptom in my post.

This is also fitted to an open system so no problems with re-pressurising the system.

[jefword]

Gingerbread Man said:

Aye, not blaming you, just think it's a daft idea to put them on your rads. Especially an open system as you can't tell if the header tank is constantly filling up as water is peeing out the other end somewhere.
A sealed system would let you know if pressure was getting out.

All masks an issue that could be rotting out your rads and sludging up your system which mounts up to a protencially bigger bill.

Just my thoughts is all. As you were!

I tried the trick of setting light to the escaping air to see if it was system corrosion causing the air in it.

However it didn't ignite, leading me to believe it was air being pulled in from somewhere. I understand these minute leaks can be hard to find as air can get pulled in by the pump through gaps where water can't escape. (Perhaps through the pump bearings)

Am I correct. Does anyone have any thoughts on this?

Also it's a bit of a bind going to bleed radiators occasionally because a tenant "can't remember" how to do them, what with all the other minor jobs some of them want doing which would take them two minutes.

Disclaimer: I do have tenants that are very good and do far more than is expected of them.