pressure reducing valve?

[diamondgas]

Yes I know what you mean DG, but water expands at a higher rate the hotter it gets 4oc being where it is most dense.

4-21oC I make that about 0.5% increase in volume. So say as an example a house contain's 30 mtrs of 15mm cold water main x 0.145ltrs = 4.35ltrs + 0.5% (0.02175) = 4.37 ltrs

I'm stuck here for a minute, i'd like to try and equate that into a pressure rise! (as I have nothing better to do with my time at the moment)

Not saying who's right or wrong, genuinely interested in this.

I like the sums With your example are you saying there'll be an increase in volume of 20ml? 4 doses of medicine It has to go somewhere though yeh? Maybe the pipework expands .... thing is with every replenishment of cold water the pipework will expand again and again ... There's something stuck in my memmory banks that says that an arrestor type ev needs to be fitted if a check valve is fitted to the mains...!

 

[Nostrum]

Might just be easier to look it up in WRAS book!! ... my head hurts reading about volumetric temperature expansion coefficients there's a fine line between plumbing and physics at times and i'm way over it at the moment!

 

[zzzjim]

........ fine line between plumbing and physics

Many thanks sambotc for the research ,

I went to bed thinking if Bends pulled in copper ,
were oval enough to work like the bent thin tube pressure guages
that straighen out as pressure rises .
​

Keen test would be hydraulic ... but you can get too interested ,
and the work just don't get done !

(Like Quantum stuff ,a pressure guage would change the pressure !)
​

 

[GQuigley67]

so why do unvented water heaters say that an EV is not required when there is say 1.5m of distance between the heater and the nearest cold water draw off, this is deemed sufficient space for expansion, i would only imagine an EV would have to be fitted if there was a CV or PRV on the cold inlet to the boiler

 

[Nostrum]

Thermal expansion rate of water: Hot Water Expansion Rate & Hot Water Pressure Increase in Hot Water Tanks or Boilers

 

[diamondgas]

Thermal expansion rate of water: Hot Water Expansion Rate & Hot Water Pressure Increase in Hot Water Tanks or Boilers

:rofl: I was on the exact same site earlier :lol:

 

[Nostrum]

Take you didn't figure it out either then! I think it worked out of be about a 0.2bar increase which would have negligible effects IMO but couldn't get a detailed answer written down as proof so to speak

 

[diamondgas]

I gave up

 

[PlumbBobBob]

just had a quick look but gave up as i didn't want to fry my brain too much

 

[Nostrum]

glad we are all in the same boat then! I understand it in principle but couldn't get the sums to work as they described, it looked to me as if the example they used was incorrect!

thinking about it, I can't see why a pressure reducing valve would be any different to a check valve in principle, but the water board haven't been fitting E/v after fitting a meter, and surely if anyone was going to see the brunt of an issue like this, they would? I'd imagine after a couple of systems popped due to check valves in the water meters, they'd be right on the case?

 

[diamondgas]

You're dead right sambotc ... Maybe my old grey matter is messing with me and I got it wrong Worth the investigation though and getting the cogs spinning a bit Cheers

 

[kay-jay]

Water board fit loose jumper stop taps specifically to allow for back expansion. As i said before if the pressure warrants it(6bar +) and thwrw is a prv and check valve fitted an arrestor or 1litre ev becomes necessary iirc

Sent from my GT-I9100 using Tapatalk 2

 

[Nostrum]

Makes a change for me being right, agreed on the cog spinning, blew out a few spider webs. Liking your new signature by the way.

 

[Nostrum]

oooh the irony, both posted at the same time kay-jay. Have you got anywhere that is written , be good to put this to bed one way or another, preferably in written confirmation.

 

[kay-jay]

Just an after thought. But what other position would a 1litre ev be used in? They make em.
so there must be a use for em and i was told they were fir cold mains on pipework between checks and prv or fixed jumper stop taps because expansion can't be taken up in any direction.....

Sent from my GT-I9100 using Tapatalk 2

 

[Mike Jackson]

Most combi manufacturers require them to be fitted if a DC valve is fitted.

 

[dancinplumba]

i use .5 lt ones

 

[diamondgas]

I didn't get the heads up on this till today .... So my grey matter didn't let me down .... if you're right kay-jay

 

[zeebeedee]

Diamond an expansion vessel is not required on a cold water main?

I hear certain boiler manufacturers are voiding warrantys when these are not fitted when a water meter is present, apparently it's causing wear and tear on boiler parts when the hot tap is closed and there is nowhere for it to go, ie non return valve on meter leaves it bouncing around the boiler.

 

[zeebeedee]

No one else heard this?

 

[diamondgas]

No one else heard this?

I think there's the potential for any of the water side gaskets to pop on the boiler ... if the expansion is so much that it takes the pressure in the domestic pipework too high?

 

[Mike Jackson]

It's in the MIs for some boilers now.

Fron the Ideal Logic instructions

important. Provision must be made to accomodate the expansion
of DHW contained within the appliance. If the DHW inlet contains a
back flow prevention device or non-return valve, e.g. a water meter,
then a mini expansion vessel should be fitted between the device and
the boiler in the cold inlet pipe.

Worcester also specify one in their instructions if a check valve is fitted, which means that you must fit one if there is a water meter.

Atag require one on all installations.

 

[Nostrum]

Is it still going!? :rolleyes4:

I think there is a bit of confusion regarding water trapped in a heat exchanger which will expand at a much higher rate than water in distribution pipework brought into a house from 10oC and warmed to 21oC room temperature.

I've looked through WRAS and I didn't see anything stating an EV was required after a pressure reducing valve on the incoming main. Personally I think it is an insignificant risk but thats me.

On a boiler after a check valve is a completely different matter and I fit one every time regardless now.