Pressure reducing valve

[Cello]

Hello guys, just joined and looking for some help/advice please

The water supply pressure at my house is 6.5 bar and it is causing a dribble from a recently installed shower valve. I would like to reduce the pressure to, say 4 bar. I have bought a WIGIG pressure reducing valve which I intend to fit to the water supply pipe. The system installed to the house is a thermal store system so, after the valve, it is essentially a closed system when all taps etc are turned off. I would welcome any advice or tips, particularly regarding the closed part of the system part of which will pass through the thermal store heat exchanger. I don't know if the pressure reducing valve will allow backflow so as the water warms up and expands, is this likely to be a problem e.g. could there be a catastrophic pressure buildup? I could fit a small diaphragm valve to the system to account for this and also help cushion the flow. Advice would be much appreciated. Thanks.

 

[Whyme]

there should be some kind of expansion device on the store hot water side like a blue or white vessal, what make cylinder is it..?

 

[Cello]

Thank you, Whyme. I had another look, there is a blue mini-diaphragm unit plumbed to the inlet to the thermal store heat exchanger. It is blue, the external diameter is approx 3 inches and the axial length approx 2.5 inches so it is quite small. I guess that I need to check it's ok and working because it must be over 20 years old. Do you have any idea what the gas-side pressure should be and should this be measured with the water- side at normal pressure or drained?

There is no obvious information re the make of thermal storage cylinder but I guess that the capacity will be approx 30 gallons and it has a header tank built into the top.

 

[AWheating]

read the manufacturers instructions from the thermal store, they normally require a pressure reducing vavle above a certain pressure. or post a picture to see if we can tell what it is.

the blue thing is probably a shock arrestor.

 

[nysk2008]

what shower valve do you have? most are tested between 5 - 15 bar, you sure its installed correctly?

 

[Whyme]

Yeah the blue is a shock arrestor probably fitted because of the high pressure, are you deffinately sure its a thermal store /unvented hot water cylinder. we need to dig a bit deeper to find out what kind of cylinder it is.

 

[Cello]

Yes it is definitely a thermal store cylinder, i.e. the bulk of the cylinder contains approx 30 gallons of (vented) water which is also part of the central heating system, i.e. the bulk hot water circulates through the boiler and radiators. The domestic hot water is derived by the mains pressure cold water passing through an (unvented) heat exchanger sited inside the cylinder, but not communicating with the central heating system water. Hope that explains the setup. I have just done a search but cannot find any reference to the manufacturer of the cylinder.

The shower valve is a Triton Altair thermostatic bar mixer valve and I am very pleased with its performance apart from the dribble when the valve is closed (please note that it doesn't always dribble, it goes through phases when is is perfectly ok but then reverts). Both inlets to the valve (i.e. hot and cold) are at mains pressure (6.5 bar). What I have noticed is that when an adjacent toilet is flushed and the cistern fills, when the level valve closes, this results in a slight spurt from the shower valve. I assume that this is due to a pressure pulse.

The shower valve was installed according to the instructions and the sales spec said that it would be ok up to 10 bar but the installation instructions only quotes 5 bar. I thought that I might get away with 6.5 bar as there is usually a bit of "fat" in most designs.

 

[Whyme]

right so the ch thermal side is open vent, if the hw side is mains pressure there must be some expansion vessal somewhere id have thought because the only unvented water systems i know of that rely on the water to expand down the cold are under sink heaters and that is governed by the lenth of pipe etc. I dont think you'll do any damage fitting a prv ( at 6.5 bar its needed really). can you post some picture of the cylinder and pipework to give us an idea pal.

 

[europhil]

Try turning the stop tap down a bit. See what happens.

 

[Cello]

How do I post a picture to this forum? I have pics of the cylinder as .jpg files.

Answering the post from Europhil, I have already tried turning down the stop tap and it makes no difference. Turning down the stop tap only restricts the flow and when all taps are turned off, the pressure will remain high in the system so suppose that this is why it makes no difference. Thanks for the suggestion, anyway.

 

[Cello]

Just realised that I can send a link to Dropbox. Here is a pic of the cylinder:

https://dl.dropbox.com/u/28021069/IMG_8704.JPG

You can see the thermostatic valve on the left that controls mixing of hot and cold water before it goes to the domestic hot water system. Below, you can see the blue "shock arrester".