Mains static pressure off the scale!!

[Barnjules]

Hi everyone,
I'm new here and would love some advice regarding my mains connection.

I'm near completing my barn conversion, and this morning filled up my system (thermal store,rads,ufh etc)with the help of my plumber(who is now gone and unavailable to ask for advice!). I fitted a new prv just after the internal stopcock as our pressure is very high here. When a tap is turned on (and whilst we were filling the thermal store),all was good,as the prv maintained the dynamic pressure at 2.5 - 3 bar. However, after plumber has left,and things were just sitting, i.e.,no taps etc on, i noticed the pressure guage on the prv was off the scale (over 10 bar). I understand this to be reading the static or standing pressure. This seems super high to me, with all taps,fittings etc that are under mains pressure having to withstand this.( i dont even know the true reading,as the gauge only goes to 10 bar,and the needle's off the scale!)

As the water supplier (southwest water) say,they have no obligation to maintain a maximum pressure, can i get a prv that reduces static or standing pressure, or is 10 bar+ normal ?? (I'm sure it's not!)

Very frustrating,and I've closed the stopcock for now..just in case : (

Any advice greatly appreciated.

Thanks,

Jules

 

[Stigster]

I don't know what types of fittings, pipework and fixtures you have in the house but as far as pipework and fittings go, 16bar on the cold seems to be a common figure for what they can reliably withstand. Outlets and fixtures is a refer to manufacturer's instructions deal usually.

As for the pressure reducing valve, the pressure reading that you see when the system is static will be the pressure on the incoming side of the valve. They usually operate on a spring loaded washer which is closed when no outlets are open. Therefore the pressure on the outlet side will not increase past the set point on the valve. Only when an outlet is opened will the water be able to flow, pushing open the spring loaded washer and only to the pressure set on the valve.

So, with a functioning PRV on the mains, your pipework and fittings will not ever get to feel this 10 bar+ pressure.

 

[Barnjules]

Thanks stigster for your quick reply. (I just typed a reply to u but the dam system seemed to have lost it..so here goes again)

You've put my mind at rest ...to a point! Out of interest,i looked on a suppliers site who ive used for most of my plumbing stuff, and they DO do a prv (for 'commercial use') that says it regulates dynamic AND static pressure,where other types only state dealing with dynamic pressure. So, i dont know what the difference is,given what you said..that my fixtures,outlets etc would never feel the 10+ bar showing on the guage when things are static.

However, i still feel a little uneasy sleeping soundly in my static caravan leaving the stopcock on overnight!

Another thing is that earlier today, my plumber wanted more pressure to fill the system, so i cranked up an old external prv (which i fitted years ago when we first got the place). He reckoned it was knackered, so i quickly removed it from the blue alkathene, only to find that his filling problem was due to an airlock somewhere! Now we have super high pressure in the caravan and i wad wondering if it was okay to re-fit it (or a new one), which will effectivley give me two in line prv's for the supply to the barn. Does this sound okay?

Any more thoughts or advice would be greatly appreciated!

Cheers, Jules

 

[Best]

This has interested me because I always thought the gauge on a PRV showed the pressure from after the valve and therefore usually 3bar for most types, which will obviously fall on taps opening and only ever rise a little on heated supplies, like unvented units

 

[Staffy85]

This has interested me because I always thought the gauge on a PRV showed the pressure from after the valve and therefore usually 3bar for most types,

yea same here, probably depends on the brand of valve fitted? , I thought same as you though , it would make sense too for confirmation of pressure being reduced.. Barnjules if you have any doubt you can buy test pressure gauges for this which can be fitted a number of different ways ROTHENBERGER Water pressure gage 0 - 10 bar - vat receipt | eBay cheaper ones out there,

 

[SimonG]

Always need to set the prv with water running.

 

[ShaunCorbs]

you put the prv the right way round?

 

[mfgs]

Interesting, I assumed them stopped the pressure increasing after the valve be it static or dynamic. You could put it to the test by installing a pressure gauge on the pipework after the pressure reducing valve.

 

[SimonG]

The gauge on the prv is after the gubbins.

 

[mfgs]

Then do they reduce static pressure or just dynamic?

 

[lame plumber]

static pressure on my road around 10 am is 16bar, dont need power showers down here. All the prvs I have installed are set around 3 bar, they never read the static pressure so I would assume yours has an issue, probably wrong way round, or knackered

 

[SimonG]

Would it have to be a governor like gas to reduce static?

 

[SimonG]

Also if you had 10 bar incoming static with a prv on an unvented cylinder with a 7 bar tprv. Why wouldn't it pass? Goes to pass at 10 bar but as soon as static transfers to dynamic at 3 bar so wont pass?

My brain is hurting. Been a long day.

 

[mfgs]

Also if you had 10 bar incoming static with a prv on an unvented cylinder with a 7 bar tprv. Why wouldn't it pass? Goes to pass at 10 bar but as soon as static transfers to dynamic at 3 bar so wont pass?

My brain is hurting. Been a long day.

haha I am the same when it comes to pressure and flow and trying to work out how they affect each other etc.

 

[mfgs]

static pressure on my road around 10 am is 16bar, dont need power showers down here. All the prvs I have installed are set around 3 bar, they never read the static pressure so I would assume yours has an issue, probably wrong way round, or knackered

That's ridiculous, bet you've never seen an booster set or an accumulator fitted near you then!

 

[lame plumber]

thinking about it, all I ever do is set the prv up under flow, never bother to check static pressure, so you could probably expect the pressure to build up slowly as the valve passes.

The only booster sets I see are in hotels with leaky systems full of corrosion

 

[Best]

If the PRV limits the static pressure beyond the valve, then surely the dynamic pressure will also be limited?

 

[lame plumber]

If the PRV limits the static pressure beyond the valve, then surely the dynamic pressure will also be limited?

you would think so.

 

[mfgs]

If the PRV limits the static pressure beyond the valve, then surely the dynamic pressure will also be limited?

They definitely do the dynamic pressure as that is how you set them up. Just not 100% sure if they also stop the static pressure build up past the valve

 

[Best]

They definitely do the dynamic pressure as that is how you set them up. Just not 100% sure if they also stop the static pressure build up past the valve

They really have to stop the static pressure past the valve. If they don't then the unvented units could build up pressure way beyond their operating normal and also everything else on the mains, like electric showers could possibly be blown apart if incoming mains was extremely high.

 

[ShaunCorbs]

+1 to the above ive never had one rise unless faulty, as the pressure in the outgoing pipe is to what the prv is set to, so if its climbs something is wrong

 

[Barnjules]

Thanks all,very interesting. It may be faulty then. I'll get the pressure tested n take it from there

 

[chris watkins]

+2 to the above above, if they fail the pressure normally drops not rises.

What is the make / model Barnjules ? or photo would be good.

The plumber wasn't adjusting it was he to get more pressure & you have released the built-up pressure before reading the gauge ?

 

[Barnjules]

No the plumber didn't touch it. (Just tweaked a weeping comp joint on it (due to the mega pressure ha!)
It's a caleffi altecnic model prescal 533. I've just found out it only controls the dynamic,not static pressure,and max inlet pressure is 12 bar! So that may be the problem. The altecnic prescal 535 however, controls static AND dynamic (for commercial applications it says?!? And 16 bar max inlet pressure) So maybe i want one of them if my incoming mains is super high n i want static reduction.

 

[ShaunCorbs]

No the plumber didn't touch it. (Just tweaked a weeping comp joint on it (due to the mega pressure ha!)
It's a caleffi altecnic model prescal 533. I've just found out it only controls the dynamic,not static pressure,and max inlet pressure is 12 bar! So that may be the problem. The altecnic prescal 535 however, controls static AND dynamic (for commercial applications it says?!? And 16 bar max inlet pressure) So maybe i want one of them if my incoming mains is super high n i want static reduction.

i would say the 533 is not for whole house pressure reducing, tbh i only use the 535 and have no problems

 

[Barnjules]

Ah,. Cheers for that corbs. I'm def gonna change it then.

 

[chris watkins]

Always thought them to be cheap and nasty (533) but never knew they were dynamic only what a silly idea almost as bad as them pressure limiting valves they supplied with the first generation of unvented units.
Still every days a school day!!

You can't beat rwc imho
312 Compact (Cold) Pressure Reducing Valves (PRVs) | Reliance Worldwide Corporation (UK) Ltd.

 

[Barnjules]

That was very helpful chris. I like the look of them..thanks a lot for your help..and thanks to everyone else for an interesting an useful thread.

Cheers

Jules

 

[Best]

That is bizarre! This has been an education.
I hadn't an idea that the 533 valve didn't actually reduce the standing pressure on whatever it supplied. You would think "Pressure Reducing Valve" was exactly that!
I always wondered why they were so cheap and fairly small bodied and now I know! I will avoid them.
Thank goodness I never had to fit one to an unvented unit.

 

[ShaunCorbs]

That is bizarre! This has been an education.
I hadn't an idea that the 533 valve didn't actually reduce the standing pressure on whatever it supplied. You would think "Pressure Reducing Valve" was exactly that!
I always wondered why they were so cheap and fairly small bodied and now I know! I will avoid them.
Thank goodness I never had to fit one to an unvented unit.

tbh i only use them for secondary prv close to a set of sinks etc (there ok in that way )

 

[Best]

tbh i only use them for secondary prv close to a set of sinks etc (there ok in that way )

It has just occurred to me that I fitted a 533 PRV solely to my brothers outside tap a few years ago because any hose connections to power washer etc, were blowing apart with the mains pressure. Once I fitted it there has never been any problem with the pressure. Surely the static pressure should have still been same?