Anti Gravity Valve? (was Re: Gravity HW/Pumped Heating - Need help)

[Jason]

After all the help from the group, I am temped to put in a second pump to go to a fully pumped system (second easiest option for me would to go to C-Plan)

Benefit of second pump is that it leaves the CH circuit - as is, and should be cheaper than S-Plan as it only needs a pump (and I might be able to get my hands on one!!), which should be cheaper and easier than having to move the pump AND need to fit 2x 2ports AND a bypass.

The only thing that is puzzeling me is the "anti gravity valve" - what does one look like, and where can you buy one from. I have looked at screwfix, discountheating, BES etc and cannot fine what I need. - can anyone point me in the right direction. I would need a 28mm fitting.

thanks

> What puzzles me on this is if, say the HW circuit was being pumped by its > > own pump and CH was off, why there would be no circulation on the CH > circuit > > without the a zone valve? > > There won't be a substantial pressure difference over the two ends of the > unpumped circuit, so flow would be non-existent or very slight, easily > stiffled by a flap type non-return valve (or the 2 port zone valve, of > course!).

[Christian McArdle]

for reliable operation, you'd need to reverse the flow direction so that the pumped flow is against the gravity flow. As this might be difficult in your situation, you may find that a conventional single check valve has more resistance in the forward direction (a bit like a silicon rather than germanium diode for electronics types out there) which should be enough to stiffle gravity circulation, at the expense of making the pump work a little harder (it should be pretty unloaded, not being expected to work the radiators).

the gravity flow is particularly strong, you may find you have no choice but to either reverse the flow somehow (so the swing valve above works) or install a 2 port zone valve. However, this is unlikely.

Christian.

[Set Square]

I fitted one in my previous house about 35 years ago! It was designed to fit in a vertical pipe, and looked like a slightly elongated pipe coupling - with a compression fitting at each end. Inside was some sort and flap, and maybe a light spring (I can't remember for sure). The principle of operation was that the flap needed a slight pressure differential before it would open. A pump could easily provide this pressure - but gravity convection alone couldn't.

I have looked for a modern equivalent - with no success so far - but will continue to look, and will post a link if I find one.

[Terry D]

The 'anti-gravity' valve is a single check valve installed in the radiator circuit from the boiler in order to prevent the upstairs radiators from warming up by thermo-syphon when only hot water is selected. The BES part number for a 28mm check valve is 8147, priced at (a very reasonable) £3.32.

Terry D.

[Set Square]

Or, in the OP's case, inserted in the (previously gravity) hot water system to prevent gravity circulation when the (newly installed) pump is not running.

It would need to be very close to the hot cylinder, *after* the vent connection, to make sure that there is still a clear path from the boiler to the vent.

[timegoesby]

These valves are only used when you have a gravity circuit. What you need to do is fit a check valve after each pump. This is normal in a 2 pump system. Then there will no circulation between CH and DHW.