use PRV on unvented cylinder or separate PRV for balanced cold feed?

[Iknowcraig]

Hi all, I am looking at having an unvented system installed and in chatting to the installer they mentioned a lot of pre-plumbed unvented cylinders have a PRV fitted which can also supply a balanced cold supply. I am fitting a new 32mm water main and understand the PRV on the unvented cylinder takes a 22mm input.

I was thinking that if I run my new main into this PRV and then run everything in the house off it to be balanced, that I will be limiting my flow due to the total 22mm supply size and therefore not getting the full benefit of my chunky new water main? Wouldn't I be better off with a 32mm MDPE>28mm copper adapter after stopcock, then T this off to take 22mm feed to the unvented system PRV and 22mm feed to a separate PRV for the cold supply to house? As long as the PRV's were set to the same pressure this would surely result in a much better potential flow for my house?

I know this is overkill but I am replumbing the whole house anyway so might as well do it in the best way possible! What does everyone think?

 

[bernardgreen]

a lot of pre-plumbed unvented cylinders have a PRV fitted

PRV = Pressure RELIEF Valve. releases water to waste if the pressure in the cylinder exceeds the safe limit, this prevents the cylinder bursting

if I run my new main into this PRV and then run everything in the house off it to be balanced,

this PRV would be a Pressure REGULATING Valve which limits the pressure in the system that it supplies.

 

[Iknowcraig]

Thanks Bernard, I was referring to the Pressure regulation valve on the unvented cylinder which regulates the incoming pressure and also has a cold water output to enable a balanced supply. I believe these are set to a specific pressure such as 3.5 bar, would there be any disadvantage to having a separate pressure regulating valve set to the same pressure?

This would then allow the full flow through the 22mm feed for hot water and the same flow for cold water rather than splitting the flow between both.

 

[fezster]

I found the 22mm megaflo pressure reducing valve was severely restricting flow in my house. I, too, had a 32mm mdpe coming in.

I had a g3 plumber upgrade the prv to a 28mm reliance valve (along with the pipework from the mdpe to the prv) and it made a dramatic difference in flow rate to my showers.

I spoke to megaflo and they said their valves should allow 100l/min flow rate. Looking at the internals of the valve, the hole is tiny, so 100l/min sounds improbable. It couldn't even manage the 50l/min I was getting from my water main. I believe some of their newer cylinders use 28mm inlets and outlets, but not sure if the prv has been updated to 28mm also.