"Adrian" wrote in message
...
HI Andrew


Andrew Gabriel wrote:
In article ,
"dennis@home" writes:

"Adrian" wrote in message
...
HI All

I've not used float-type auto air vents before - so I may be doing
something wrong - expert advice welcomed !
The float vent I have in my hand has a screw on the top that appears to
close the vent even if the float is not floating.
I believe it is really for fast filling a pressurised system and not
actually an auto vent to release trapped air.
It looks like you open it to let the air out while filling and then
close it to ensure air can't get drawn in by the circulating water.

The closing is because they don't last long if left open. The ball has
to stay wet to seal, and this means there's moisture exposed. This dries
and eventually leaves deposits behind, and these build up and stop the
seal working, so the valve starts leaking water.

Ah - so they're not so much an auto-air-vent - more of an
'auto-air-seperator-with-manual-vent' - I didn't realise that.

So in normal operation you'd leave them with the cap screwed down tight -
and release any trapped air by unscrewing the valve from time to time...?

Auto air vents are for filling purposes sonly. Once filled, the screw
should be tightened.

You should look at why air is being drawn in - or is it corrosion?
Look at where the cold feed & open vent pipes from the F&E tank is. The
relationship of these and the pump may solve matters.

Having an auto air vent permanently open will solve nothing as all it will
do is advance corrosion as air is being drawn in.