Pressure Reducing Valve ( PRV ) Position

[Onoff]

Evening,

 

On the mains water I'm running 25mm MDPE in to connect to 15mm copper. I can get a PRV with these fittings either side. Is it usual to put the stopcock before or after the PRV? I can see the argument either way.

 

Cheers

Edited August 23, 2016 by Nickfromwales
PRV can be Pressure Relief Valve also ;). Title edited for clarity.

[PeterW]

Both ... 

 

MDPE stop valves aren't that expensive but make sure it's full bore. Then add a full bore lever valve and you will be able to isolate both the house and the PRV of you need to do any maintenance on it 

[Onoff]

42 minutes ago, PeterW said:

Both ... 

 

MDPE stop valves aren't that expensive but make sure it's full bore. Then add a full bore lever valve and you will be able to isolate both the house and the PRV of you need to do any maintenance on it 

 

Cheers. So you're  saying:

 

- incoming MDPE

- MDPE stop valve

- short length of MDPE

- MDPE to 15mm copper PRV

- 15mm copper

- full bore lever valve

 

?

[Nickfromwales]

If this is a G3 certifiable UVC install then there's far more to it   

Options are....

1) new install.

2) retro fit. 

 

1)....

Stopcock.

NRV.

Drain-off cock.

NOTE: This is where you should now tee off for the outside tap so it is not affected by the pressure relief valve. Ensure that the outside tap has an integral non-return valve. 

Pipework to UVC location.

Cold feed to multi-block with a local isolation immediately prior to. ( 22mm 1/4 turn lever valve ).

Multi-block located within 500mm of the UVC it serves ( G3 / manufacturer requirement ).

Balanced cold feeds all to be fed from the balanced output of the multi-block ( mixer taps / shower valves / thermostatic devices etc ). 

Therefore no requirement for non-return valves on any mixed feed outlets as all mixers will be at the same potential, regardless of static or dynamic fluctuation. 

 

2)....

Stopcock.

NRV.

Drain-off cock. 

Secondary Pressure Reducing Valve ( in addition to the manufacturer supplied one which has to be mounted at the UVC position as stated above ( so no, you can't nick it and fit it here )). 

Pipework to UVC location.

Cold feed to multi-block with a local isolation immediately prior to. ( 22mm 1/4 turn lever valve ).

All house water pressure is governed by the secondary PRV so the cold feeds can be tapped into anywhere in the house without causing pressure differential issues between hot and cold whatsoever. 

Hot outlet of UVC MUST have a single check non-return valve in line with flow. This is a final failsafe for instances where the secondary PRV fails and mixer taps then can back feed the UVC and over pressurise it to the point of failure. Retro fit only. 

 

Failure to adhere to these particulars is what keeps me in a job .

 

 

[joe90]

I must admit I was thinking of installing a PRV, Because my pressure seems high but I have not measured it and notice that screwfix sell a pressure gauge for £14.99 so, what is a normal pressure range for a house? ( the push fit hose connections sometimes "blow" and may be down to high pressure.

[Nickfromwales]

1 minute ago, Onoff said:

 

Cheers. So you're  saying:

 

- incoming MDPE

- MDPE stop valve

- short length of MDPE

- MDPE to 15mm copper PRV

- 15mm copper

- full bore lever valve

 

?

 

25mm to 22mm stopcock. Brass or plastic. NOT 15mm

All cold feed pipework to UVC should be 22mm, is this possible ?

[Nickfromwales]

Just now, joe90 said:

I must admit I was thinking of installing a PRV, Because my pressure seems high but I have not measured it and notice that screwfix sell a pressure gauge for £14.99 so, what is a normal pressure range for a house? ( the push fit hose connections sometimes "blow" and may be down to high pressure.

Replaced an UVC in a £1M house, and the guy said the pressure was high. I out my gauge on the outside tap and it went to 10bar and the needle bent so badly I had to bin it. 

Surveying the static cold mains pressure is absolutely critical and should never be overlooked. 

[Onoff]

1 minute ago, Nickfromwales said:

 

25mm to 22mm stopcock. Brass or plastic. NOT 15mm

All cold feed pipework to UVC should be 22mm, is this possible ?

Hope, not at the moment or easily. All the mains cold is in 15mm copper. And I  don't  yet have a UVC.....

[Nickfromwales]

1 minute ago, Nickfromwales said:

Replaced an UVC in a £1M house, and the guy said the pressure was high. I out my gauge on the outside tap and it went to 10bar and the needle bent so badly I had to bin it. 

Surveying the static cold mains pressure is absolutely critical and should never be overlooked. 

They had 'top plumbers' fit the original UVC . Then it went pop in the upstairs airing cupboard. Oopsy. 

[ProDave]

Top tip. do NOT connect a PRV to newly installed plumbing.

 

I did that when our water to site was first installed and I wanted to reduce the pressure to the static 'van.

 

The PRV did not work. With no flow, the pressure slowly crept up.

 

I stripped it down and it was full of grit from the new, unpurged pipework. Cleaned it out, re assembled and it now works.

 

so I guess what I am saying is on a new install make provision to fit it but fit a bypass until everything has been purged and is nice and  clean.
 

[joe90]

Can anyone give me an acceptable range of pressure I should have?

[Onoff]

Cheers. And thanks Dave for the PRV tip too. It's  all gone seriously t!ts up tbh this week. Temporary repair on the water main failed to the point where the failing iron is now under the house footings. 

 

No option but to renew it all the way. Where I want to bring it in now means taking the remaining downstairs wc out for access. Sods Law the mains water needs to come in under this wall right where the 3" downpipe is. Fighting on all fronts at the mo!

 

 

 

Edited August 24, 2016 by Onoff

[Nickfromwales]

3 minutes ago, ProDave said:

Top tip. do NOT connect a PRV to newly installed plumbing.

 

I did that when our water to site was first installed and I wanted to reduce the pressure to the static 'van.

 

The PRV did not work. With no flow, the pressure slowly crept up.

 

I stripped it down and it was full of grit from the new, unpurged pipework. Cleaned it out, re assembled and it now works.

 

so I guess what I am saying is on a new install make provision to fit it but fit a bypass until everything has been purged and is nice and  clean.
 

Good point, a lot of failure is down to shite in the valve. The strange part is that the stainless gauze filter is on the incoming side normally so doesn't usually allow over pressure events, just poor flow / low pressure. 
You really shouldn't fit any bypass as that will allow full range pressure to get to sensitive equipment. We all know that 'temporarily fitted measures' always end up never getting changed to the way they should so I'd advise against that tbh.

All relief valves will have installation practices clearly stated, as in "thoroughly purge all primary pipework prior to commissioning the valve" etc etc. That takes care of any lumps of solder, flux etc, and then the integral stainless gauze filter in the PRV takes care of any subsequent crap. Annual cleaning of the filter and checking of the set / operating / actual pressure is also paramount. 

On the PRV's I always fit a primary and secondary pressure gauge so I can see the incoming and secondary pressure differences. If they both match, your in need of maintenance ( or your pressure is lower than the set value of the valve ). 

[Nickfromwales]

5 minutes ago, Onoff said:

Cheers. And thanks Dave for the PRV too. It's  all gone seriously t!ts up tbh this week. Temporary repair on the water main failed to the point where the failing iron is now under the house footings. 

 

No option but to renew it all the way. Where I want to bring it in now means taking the remaining downstairs wc out for access. Sods Law the mains water needs to come in under this wall right where the 3" downpipe is. Fighting on all fronts at the mo!

 

 

 

Any chance to get it redirected so you can upsize the incoming cold mains to 22mm?

[Nickfromwales]

10 minutes ago, joe90 said:

Can anyone give me an acceptable range of pressure I should have?

Pressure and flow are location dependant tbh. 

You should be 'given' 1 bar static at least, and should receive around 11-12 litres per minute of dynamic flow. 

You can check the latter with a weir cup 

[Onoff]

8 hours ago, Nickfromwales said:

Any chance to get it redirected so you can upsize the incoming cold mains to 22mm?

 

I will look at getting to 22mm after the 25mm MDPE so at least there's  some provision for later. It may be that for now it has to stay in 15mm thereafter via a reducer.

 

So I'm basically looking to change the position of the incoming mains more out of necessity than choice as to "where". What I have (luckily?) is a 15mm copper drop coming out of the loft to feed the antiquated downstairs wc cistern and cold for the basin. This wc is in fact at the end of a corridor hived off of the big downstairs bedroom. Wall to the left is a stud separating the bedroom, wall to the right is solid brick/block separating the totally gutted, being refurbished, downstairs bathroom (the saga of which can be found elsewhere ).

 

So the old, downstairs wc, mains in 15mm copper coming down on the right:

 

 

In the "corner": Mains 15mm coming down, teeing off to the wc and on round to the basin. The 22mm hugging the floor with the push fit elbow is the single pipe CH system that skirts the perimeter of the house. This was the (again temporary) "bypass" I did when I got rid of all the pipes in the adjacent gutted bathroom:

 

 

The fact I've already had this wc out and floor up is filling me with joy.....not!

 

When I had the floor up before. Coming in from the right, thru the wall, is the old cold, cws feed to the basin now replaced by mains feed:

 

 

 

The fact I've even got this pipe is a by product of when I gutted ALL the pipework in the main downstairs bathroom and ran it as a "temporary" thing.  The plan is for the new MDPE mains to come up thru the floor from outside and feed this pipe. And there lies more fun!

 

The 15mm drop is literally the other side of where the main drop of this black downpipe is:

 

 

Bottom left, above, you can see the hole where the old iron mains went through the footings. And close up:

 

Putting a PRV there in terms of accessibility isn't maybe the best location but get ho! 

 

As for make of PRV, well S,fix is closest (and cheapest maybe)

 

Sorry I didn't come back last night. Banging headache, it was 2 Neorofen and night night's for me!

 

HTF do all my threads crossover so much? Every job clashes or gets help up by another! So much for a week on leave, even the drinks not helping! 

 

Mind you I'd be lost without the BiL and his digger as and when he's free. I really could do with one tbh.

 

Back to the task in hand I'm thinking this MDPE stopcock as the first think after the pipe:

 

http://www.screwfix.com/p/floplast-mdpe-plastic-stop-cock-25mm-x-25mm/28809

 

 

Then this 22mm/25mm adapter:

 

http://www.screwfix.com/p/floplast-copper-mdpe-adaptor-kit-22mm-x-25mm/25970

 

 

Followed by this PRV:

 

http://www.screwfix.com/p/honeywell-pressure-reducing-valve-with-guage-22mm/4671j

 

 

 

 

Cheers 

Edited August 24, 2016 by Onoff
Photos added

[Nickfromwales]

A little boxing in at the side of that cloak wc and IMO that's a great place for the stopcock and PRV to reside long term. .

Can you take the outside tap from there too? I'd recommend doing that even if it puts the OT in a less convenient position. Reason being is that the tap will have full bore mains BEFORE the PRV, and leave the shower etc less affected from the OT being used. 

If possible.....

25mm mdpe to 22mm brass stopcock. ( if you use mdpe stopcock you'll need another fitting ( internal reducing set ) to get to copper and you'll not be able to solder right next to it as it's nylon / rubber etc ). 

22x22x15mm ( centre ) tee picking up the loo and outside tap. 

22mm PRV. 

22x22x15 ( centre ) tee for 15mm Drain-off cock. 

22x15mm reducer feeding into existing 15mm drop. 

 

( don't forget to get a pressure gauge with the PRV so you can calibrate / reset at maintenance intervals / one-glance check for correct function ). 

 

 

[joe90]

Sorry to be picky but is there a "normal" max pressure for domestic plumbing so that things like washing machines and taps are not working too hard?

[Onoff]

 

3 minutes ago, joe90 said:

Sorry to be picky but is there a "normal" max pressure for domestic plumbing so that things like washing machines and taps are not working too hard?

 

I'm going to dive in and say 3 bar and then someone else will correct me.....

Edited August 24, 2016 by Onoff

[Onoff]

11 minutes ago, Nickfromwales said:

A little boxing in at the side of that cloak wc and IMO that's a great place for the stopcock and PRV to reside long term. .

Can you take the outside tap from there too? I'd recommend doing that even if it puts the OT in a less convenient position. Reason being is that the tap will have full bore mains BEFORE the PRV, and leave the shower etc less affected from the OT being used. 

If possible.....

25mm mdpe to 22mm brass stopcock. ( if you use mdpe stopcock you'll need another fitting ( internal reducing set ) to get to copper and you'll not be able to solder right next to it as it's nylon / rubber etc ). 

22x22x15mm ( centre ) tee picking up the loo and outside tap. 

22mm PRV. 

22x22x15 ( centre ) tee for 15mm Drain-off cock. 

22x15mm reducer feeding into existing 15mm drop. 

 

( don't forget to get a pressure gauge with the PRV so you can calibrate / reset at maintenance intervals / one-glance check for correct function ). 

 

 

 

How do I go from 25mm MDPE to a 22mm brass stopcock? I see in S'fix they have this but poor reviews:

 

http://www.screwfix.com/p/poly-stop-cock-22-x-25mm/97324#product_additional_details_container

Edited August 24, 2016 by Onoff

[Nickfromwales]

5 minutes ago, joe90 said:

Sorry to be picky but is there a "normal" max pressure for domestic plumbing so that things like washing machines and taps are not working too hard?

Most PRV's are factory set at either 3 or 3.5bar. If you have over that ( static ) then I'd run at around 4 bar as that makes quite a difference to the flow rate. Only noticeable if there is say 5-6 bar incoming. 

[Nickfromwales]

With one of these.

Don't forget the insert. 

[Nickfromwales]

Ttfn.  

[Onoff]

Thanks as always.

 

And it's off to S'fix we go!

 

 

[PeterW]

On that last 22-15 reducer, if you use a 22mm compression coupler with a reducing set in it you won't have to do any rework to it when you move up to 22mm throughout ...