Hot water pipe 'inline air release valve' - Question

[Laurencebn10]

Hi,

DIY homeowner here.

Ist floor of house. Front bathroom hot water draws from cylinder which is heated by the Greenstar 28i Junior Combi located on the same floor. To get from cylinder to bathroom, the water goes up, horizontally over a stairhead, and back down into the bathroom.
After pumped bath is run, we often get an airblock to bathroom that I have to clear by running a pipe from the rising main!
I remembered that when this was all plumbed years ago, the plumber told me he'd placed an air vent in the horixontal run over the stairhead (the highest poiunt on the journey), so yesterday I cut away some plaster to take a look. (See picture)
I'm confused. This just looks like an ordinary inline flow valve to me, mounted on the vertical of a copper T join soldered into the pipe. If I have the screw set to horizontal, as you'd expect, the water just flows through the pipe. If I turn it 90 degrees the water spurts out of the top of the valve.

Is that actually an air vent valve, or is there meant to be an auto air vent valve screwed into that T with the valve slot then turned to the vertical?

If it needs an auto air vent, please could you give me a link or at least the name of exactly what to buy?

Thank you - Laurence

 

[Ric2013]

It's an isolation valve. You could use it to purge air, but you'd have to do so manually, which is acceptable if it is only to set the system up, but fairly annoying if you have to do it often.

I assume your idea is to fit a bottle air vent. There is a slight problem with this in that you might be creating a dead leg in which the water can fester and bacteria can breed, so try to keep that leg short. As they aren't usually used for potable water, they probably won't make sure the materials used are 'safe' for potable water either. Oddly, the "Mira's Guide to Pumped Showers" (p. 40, see online) advocates their use (though note they do it on the pressure side of the pump), so you may want to give Mira a call and ask if they can recommend a specific brand that is suitable. My concern would be another, however: if that section of pipe with the bottle air vent is subject to vacuum, then the pump might suck in air through the air vent itself and so you'd solve the airlock issue but your pump would probably work exceedingly badly.

What would be better would be to tackle the problem at source. If your pump is sucking air into the hot water line, therein lies your problem. It won't be doing the pump any good either. Pumps like to push water but should have positive gravity-fed pressure at their inlets even when they are running, not a vacuum. The pump should have a dedicated feed from the cylinder, either using a proprietary flange or using the kind of technique Mira suggests on p. 22. Incidentally, I don't entirely agree with Mira's idea that having long angled sections of pipe is a good thing for the reason that allowing water to circulate in a pipe to avoid wasting water wastes heat (higher cost and carbon) instead of water, but the idea of a tee off the bottom of a short section of angled pipe can work very well.

Bodge alternative is that you could make sure all other taps are turned off and don't let in air in vacuum conditions, though a vacuum should not really exist at all.

 

[Laurence]

Ric - Thanks so much for such a clear and thorough answer. Really appreciate it being written so I could understand it!

Laurence

It's an isolation valve. You could use it to purge air, but you'd have to do so manually, which is acceptable if it is only to set the system up, but fairly annoying if you have to do it often.

I assume your idea is to fit a bottle air vent. There is a slight problem with this in that you might be creating a dead leg in which the water can fester and bacteria can breed, so try to keep that leg short. As they aren't usually used for potable water, they probably won't make sure the materials used are 'safe' for potable water either. Oddly, the "Mira's Guide to Pumped Showers" (p. 40, see online) advocates their use (though note they do it on the pressure side of the pump), so you may want to give Mira a call and ask if they can recommend a specific brand that is suitable. My concern would be another, however: if that section of pipe with the bottle air vent is subject to vacuum, then the pump might suck in air through the air vent itself and so you'd solve the airlock issue but your pump would probably work exceedingly badly.

What would be better would be to tackle the problem at source. If your pump is sucking air into the hot water line, therein lies your problem. It won't be doing the pump any good either. Pumps like to push water but should have positive gravity-fed pressure at their inlets even when they are running, not a vacuum. The pump should have a dedicated feed from the cylinder, either using a proprietary flange or using the kind of technique Mira suggests on p. 22. Incidentally, I don't entirely agree with Mira's idea that having long angled sections of pipe is a good thing for the reason that allowing water to circulate in a pipe to avoid wasting water wastes heat (higher cost and carbon) instead of water, but the idea of a tee off the bottom of a short section of angled pipe can work very well.

Bodge alternative is that you could make sure all other taps are turned off and don't let in air in vacuum conditions, though a vacuum should not really exist at all.

 

[Laurencebn10]

It's an isolation valve. You could use it to purge air, but you'd have to do so manually, which is acceptable if it is only to set the system up, but fairly annoying if you have to do it often.

I assume your idea is to fit a bottle air vent. There is a slight problem with this in that you might be creating a dead leg in which the water can fester and bacteria can breed, so try to keep that leg short. As they aren't usually used for potable water, they probably won't make sure the materials used are 'safe' for potable water either. Oddly, the "Mira's Guide to Pumped Showers" (p. 40, see online) advocates their use (though note they do it on the pressure side of the pump), so you may want to give Mira a call and ask if they can recommend a specific brand that is suitable. My concern would be another, however: if that section of pipe with the bottle air vent is subject to vacuum, then the pump might suck in air through the air vent itself and so you'd solve the airlock issue but your pump would probably work exceedingly badly.

What would be better would be to tackle the problem at source. If your pump is sucking air into the hot water line, therein lies your problem. It won't be doing the pump any good either. Pumps like to push water but should have positive gravity-fed pressure at their inlets even when they are running, not a vacuum. The pump should have a dedicated feed from the cylinder, either using a proprietary flange or using the kind of technique Mira suggests on p. 22. Incidentally, I don't entirely agree with Mira's idea that having long angled sections of pipe is a good thing for the reason that allowing water to circulate in a pipe to avoid wasting water wastes heat (higher cost and carbon) instead of water, but the idea of a tee off the bottom of a short section of angled pipe can work very well.

Bodge alternative is that you could make sure all other taps are turned off and don't let in air in vacuum conditions, though a vacuum should not really exist at all.

 

[Laurencebn10]

Hi Ric - thanks you so much for taking time to post this easy to understand and very comprehensive reply. I've now fitted the bottle air vent (along with a small hatch door in the plaster so I never need to hack plaster out again!!!). I'll keep an eye on it now based on your post to see whether it a) solves my problem or b) causes any of the possible side effects you flagged. Really appreciate your help.