Non Return valves on feeds to PEV?

Ads17 · 9 Dec 2013

I have a bath shower mixer tap which has been installed for some time and is fed from Mains cold and Gravity hot. As this is unbalnced it meant it was difficult to get an even temperature when using the shower as any minor adjust meant the temperature would go from warm to either scolding or freezing. As the bathroom was getting a bit of a tidy up I decided to try and get the shower working better. After looking into many options I opted to install a Pressure Equalising Valve. Fitting the PEV has fixed the shower temperature issues we were having but I have quickly relised that at the PEV the mains cold is being backfed into the hot supply and leaving us with no hot water.

My understanding is to get round this I need to put a Non Return Valve (Check Valve) on the Hot supply feeding the PEV to stop the cold being backfed to the HW Cylinder. Is this correct and would I also need to put a Non Return Valve onto the Cold supply feeding the PEV too?

Charnwood · 10 Dec 2013

If you're getting 'cross-contamination' I'd say the PEV is faulty.
It would probably have been easier and cheaper to fit a Pressure Reducing Valve on the cold supply.

elijuh · 10 Dec 2013

As said above, a pressure reducing on the cold mains seems more appropriate. Consider testing both hot and cold pressure at full bore if possible. Add a non return valve, sure, but if it's on the hot outlet, and you've already got a problems with system balancing - it'll only hinder the pressure and flow.

Secondly that cross contamination your facing is not a good thing at all, both for your pipes and safety wise. It is symptomatic of someone attempting to address an issue he should instead have solicited with the correct person.

2 Options
Pressure Reducing Valve
If you have a CWSC get a plumber to implement a demand for the shower from it. If you don't then good luck to ya.

Ads17 · 10 Dec 2013

Adding a Pressure Reducing Valve was somthing I looked into originally but couldn't find a suitable one.
There is a PRV on the mains cold water as it enters the house and registers 2.5bar. The gravity fed HW has a 2-3m drop so expecting approx 0.3bar on the HW.
Non of the PRVs I saw had a range less than 1 bar so the minimum I could set the cold water too would have been 1 bar which would still be to high in terms of balancing.

Charnwood · 10 Dec 2013

Is the PEV capable of handling a 10:1 differential?

Ads17 · 10 Dec 2013

Yes, apparently it must not exceed 20:1

GavThePlumber · 10 Dec 2013

Putting a check valve on the hot would sort the issue, putting one of the cold might satisfy the regs, but in real terms not be necessary.

The problem shouldn't exist in the first place though and as mentioned, the PEV may be faulty as it is sending water back into the tank.

Agile · 10 Dec 2013

I am not very familiar with those valves as I don't see them as a very useful solution.

However are you sure its been correctly connected?

I would have expected most reducing valves to give an output below 1.0 Bar.

Many work best when not reducing too much. Often two in series are better.

Tony

Charnwood · 10 Dec 2013

Agile said:
I would have expected most reducing valves to give an output below 1.0 Bar.

Most PRVs go to 1 bar, although some are available that will go down as far as 0.5 bar.

picasso · 10 Dec 2013

Get rid of the PEV and check valves they are never going to work properly, have you looked at venturi showers ?

GavThePlumber · 10 Dec 2013

Nah, they do work fine, been ages since i installed one, as most people just choose to have an electric shower, which on these older properties normally means having a better flow thus better shower.

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Non Return valves on feeds to PEV?

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