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Discuss Shower option - cast your vote! Cold from loft tank VS Pressure Equalising Valve? in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

Cold from loft tank VS Pressure Equalising Valve?

  • Cold from loft tank

    Votes: 3 100.0%
  • Pressure Equalising Valve

    Votes: 0 0.0%

  • Total voters
    3

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Messages
89
First - an apology for monopolising the forum with all my plumbing questions! I'm hoping this will be my last and I'll move onto something else (like choosing a woodburner, which is the next thing on the to do list)...

My situation... We've having a bathroom refit and will have a new bath with shower mixer tap. We've got an oil boiler and vented system. We're eco minded and are happy with a very weak shower. In fact, that's our preference. So we don't want to install a pump, shower power, new unvented cylinder, etc. etc. There will be another shower in the house too. The cold is currently mains.

I've narrowed it down to two options:

1. Put a pressure equalising valve under the bath so the hot and cold have matched pressure.
2. Run a cold feed from the tank in the loft, so both hot and cold are gravity fed. (The tank is 40 Gallon actual / 60 Gallon nominal).

Some relevant points for both 1 and 2:

  • Is a 40/60 gallon tank large enough to run the cold and hot from?
  • The tank isn't far away from the bathroom ceiling, so wouldn't need a long run of pipe to get to he shower mixer tap
  • The pipe from the loft would be coming down the tap end wall of the bath, so would need to be chased in / tiled over. However, the mains cold goes up to the loft on the wall too, so there's already a pipe being chased in there...
  • The mains cold comes up from the room below where the bath will be (tap end)
  • The bath panel will be removable, so accessing the PEV wouldn't be an issue
  • Future proofing... Hopefully the boiler has years left in it, but if/when it goes we don't know what we'll go for next. Are PEVs useful in unvented and/or combi boiler set ups (when used with bath shower mixer taps)? I've read very opposing answers to that question!
  • I presume performance will be similar in both set ups, so if there's likely to be a big price difference between the two then that might help decide.

I'll add a poll for the sake of it.

A vote, or a thought on any of the above, would be most welcomed.

Many thanks and have a great weekend everyone.
 

Ric2013

Plumber
Messages
3,483
You're eco minded, so of course 40 gallons is enough. Problems are only likely if you were to pump the water which you aren't. I'm always in favour of low-tech over fancy complicated stuff that will go wrong.

Although we can pretend fancy complicated stuff will make us net carbon zero by 2050 bla bla bla (which of course is far too late).
 

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89
Although we can pretend fancy complicated stuff will make us net carbon zero by 2050 bla bla bla (which of course is far too late).

Must admit, I'm not feeling too confident about the future either.

I'm always in favour of low-tech over fancy complicated stuff that will go wrong.

Fair play, that makes sense. I'm not too familiar with how PEVs work. Do you know if they go wrong quite frequently? Is it the case that unvented cylinders have PEVs?

Thanks for your help
 

Ric2013

Plumber
Messages
3,483
Fair play, that makes sense. I'm not too familiar with how PEVs work. Do you know if they go wrong quite frequently? Is it the case that unvented cylinders have PEVs?
To be honest, neither am I. I would imagine they would be reliable provided they are used regularly (i.e. not left several months between uses). I just realise the tendency is to make everything increasingly technical and I'm not sure I approve.

FWIW, the house I grew up in had a semi-gravity heating system which had no attention (not even a service) for 15 years (then the cylinder needed replacing - it was old, after all). The house I bought when I moved out from my parent's home has a Y plan system with a three-port valve. In 15 years, I have replaced the three-port valve actuator two or three times, and the entire valve once. I have also had a new fan and PCB on the boiler. I can live with this, as it is more fuel efficient as a system, but you can see, I hope, my line of thought.
 

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89
To be honest, neither am I. I would imagine they would be reliable provided they are used regularly (i.e. not left several months between uses). I just realise the tendency is to make everything increasingly technical and I'm not sure I approve.

FWIW, the house I grew up in had a semi-gravity heating system which had no attention (not even a service) for 15 years (then the cylinder needed replacing - it was old, after all). The house I bought when I moved out from my parent's home has a Y plan system with a three-port valve. In 15 years, I have replaced the three-port valve actuator two or three times, and the entire valve once. I have also had a new fan and PCB on the boiler. I can live with this, as it is more fuel efficient as a system, but you can see, I hope, my line of thought.

Hi

Yes, I think I follow. The house you live in now is more reliant on techno, with more things to go wrong, and so has been more bother over the years with things needing replacing? I'm not so sure what a "semi-gravity heating system" is though, so can't compare. I'm still learning!!

As to what I'm going to do, I'm still undecided....

Does anyone else have experience with PEVs and/or care to comment on how reliable they are?

Are there any scenarios with an unvented or combi system where a PEV might be useful? The product blurbs all say "suitable for unvented and combi systems," but from what I understand both of these have equal pressure, so why would anyone use one with those systems? Does it change things if a shower/mixer tap is being used rather than anything thermostatically controlled?

Many thanks
 

Ric2013

Plumber
Messages
3,483
Are there any scenarios with an unvented or combi system where a PEV might be useful? The product blurbs all say "suitable for unvented and combi systems," but from what I understand both of these have equal pressure, so why would anyone use one with those systems? Does it change things if a shower/mixer tap is being used rather than anything thermostatically controlled?

Many thanks
Well, in practice pressure with a combi system may not always be completely equal. There is a difference between standing pressure and working pressure (if you imagine a combi has a limited flow and you open the hot tap fully, the pressure at the inlet of that hot tap may be lower than on the cold tap where there is no such restriction to flow in the pipeline).

I can't see it being especially likely that problems would arise in the systems you mention, but I can see that if there is a non-thermostatic shower installed, there could be circumstances where someone flushing a toilet or opening a cold tap elsewhere might cause the shower to suddenly get hotter. As you suggest, you'd hope a thermostatic device would be quick enough to avoid scalding without pressure equalisation.

It has occurred to me that these pressure equalising valves are really designed for cases where it is not practical to correct old pipework design that may not be 100% as you would design it for current circumstances (leading to circumstances as above) and are more to even out fluctuations in pressure than to even out unbalanced pressures. Looking at a Reliance brand data sheet online, Reliance's product is designed for minimum 0.3bar operating (working) pressure. It is unlikely that you'll have 3 metre head of working pressure on your hot (height of cold water cistern above the tap minus any losses due to pipe internal friction) so may not be suited to your application anyway, depending on the specification for your valve. Should have mentioned this earlier really :)
 

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89
Thanks as every @Ric2013

Interesting what you say about combis, and so perhaps with a simple shower mixer (part of the taps/non-thermostatic) and a combi, the PEV would be helpful...

From what I've been led to believe, the PEV reacts quite quickly, so when someone uses water elsewhere in the house it will adjust automatically straight away to still maintain equal pressure. I was pleased to find that out :)

I'm not sure, but I think I read somewhere that they might be used in places like hospitals and hotels so that at every outlet that matters there's equal pressure and no fluctuations, regardless of who's using what where. But don't quote me on that!

As for the minimum pressure, thanks for pointing that out. Luckily the other two main brands (Altecnic and Deva / Methven - have a minimum of 0.2bar. Because it's measured at the unit - which will be under the bath - I'll have a head of around 0.25bar there, so all good.

Cheers
 

Ric2013

Plumber
Messages
3,483
From what I've been led to believe, the PEV reacts quite quickly, so when someone uses water elsewhere in the house it will adjust automatically straight away to still maintain equal pressure. I was pleased to find that out :)
I would imagine it would. Sorry if I was unclear - my point was that if the mixer were thermostatic, the PEV may not be so important.

I'm not sure, but I think I read somewhere that they might be used in places like hospitals and hotels so that at every outlet that matters there's equal pressure and no fluctuations, regardless of who's using what where. But don't quote me on that!
The regulations are getting increasingly strict in the UK as regards the possibility of scalding due to pressure or temperature fluctuations, and even more so in care environments. Plus we've gone down the American litigation route so it's probably rather common for institutions to cover their backsides by going above and beyond.

As for the minimum pressure, thanks for pointing that out. Luckily the other two main brands (Altecnic and Deva / Methven - have a minimum of 0.2bar. Because it's measured at the unit - which will be under the bath - I'll have a head of around 0.25bar there, so all good.
If you do go for the PEV, do let us know how you get on. I'm always keen to experiment with what works and what doesn't but obviously I can only really do this in my own house. I have separate hot and cold taps and an electric shower so it's not really something I could play with at home short of setting up a test rig.
 

Reply to Shower option - cast your vote! Cold from loft tank VS Pressure Equalising Valve? in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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