Pressure reducing valve restricting flow?

[vetinry]

Good morning all

I'm just trying to understand the impact of pipe diameter on flow. As part of a big renovation of our house, we've been having quite a bit of plumbing and heating work done.

We've moved from a gravity to mains pressure hot and cold water, and the plumber has recommended putting pressure reducing valves on the hot and cold feeds (we have them being supplied by 2 seperate mains).

For the cold feed, the old stopcock under the sink was leaking and so he's replaced it with a 28mm lever valve linking between the 32 MDPE mains pipe and the 22mm cold water pipe that runs through the house.

But then he's put a 15mm pressure reducing valve after the gate valve and before the existing pipe work. I've asked him about this and he says it doesn't matter and won't affect flow.

Is this right? I would have thought that trying to preserve as much of the incoming pipe diameter throughout the property would have resulted in good flow rates?

Cheers

Steve

 

[Nat]

In my opinion this will surely affect the flow rate but to what extent I couldn't tell you. Essentially this is creating a bottleneck in the pipework. Why not fit a 22mm prv?

 

[PlumbBobBob]

i agree ask for a 22mm prv still reduces pressure but keeps flow

 

[GrahamM]

You are correct in your assumption as the lads have confirmed.
Ideally I would want 22mm pipe ran as far as practical to all outlets before stepping down to 15mm.
Your flow rate will be reduced stepping down to 15mm at the mains inlet.

 

[SimonG]

If it's 22mm pipe you want a 22mm prv, need to preserve as much flow as possible and as Nat said it will be a restriction.

 

[andyplumber]

have u got a unvented cylinder as part of your hot water mains pressure or a combi boiler, if you have a unvented cylinder you don't need a pressure reducing valve after the stopcock as one will be fitted at the cylinder or should be and that will reduce the pressure for your hot water.

what the plumber has done will affect the flow rate but as said above to what extent i don't know.. can you take a picture of what the plumber has done

 

[SimonG]

have u got a unvented cylinder as part of your hot water mains pressure or a combi boiler, if you have a unvented cylinder you don't need a pressure reducing valve after the stopcock as one will be fitted at the cylinder or should be and that will reduce the pressure for your hot water.

what the plumber has done will affect the flow rate but as said above to what extent i don't know.. can you take a picture of what the plumber has done

Although I agree with what you have stated if you are going to have trouble getting a balanced cold from the unvented cylinder then to fit the prv at the stop tap is a good alternative. I always try and fit it after the take off to kitchen sink/outside tap so you still have good pressure at these outlets. But as everybody as stated, should be 22mm.

 

[kay-jay]

hmm the effects of pipe diameter on flow are probably best summed up in the following example.

a man peeing a litre a minute vs a stallion peeing a gallon a minute :stuart:

 

[Gray0689]

hmm the effects of pipe diameter on flow are probably best summed up in the following example.

a man peeing a litre a minute vs a stallion peeing a gallon a minute :stuart:

Very good description mate lol
Ideally the balanced cold should come from combination valve at new cylinder but if it can't be done from here then as Simon says lol prv at mains will still do it but deffo 22mm if reduce down here then it defeats the purpose of running 22mm to cylinder as MIs will state

 

[vetinry]

Thank you for all of the replies.

At least I wasn't going completely mad when I thought it was strange to fit a 15mm PRV. Looking at it, it doesn't look shiny new and so I wonder if it's just something he had left over.

Just to help with the comments on balancing, the property seems to have 2 mains feeds into it. The one under the sink is 32mm MDPE and is being used to supply cold water. This had a slight leak on the main stopcock and so my plumber has replaced this with a 28mm lever ball valve, which then goes into the 15mm PRV and then back into 22mm pipework which supplies the house.

In the garage, there is the second mains feed - this appears to be smaller MDPE (20mm) and he's used this to feed the unvented cylinder, which is installed in the garage too (lots of information about this in the central heating section from a few weeks back). And yes, this does include a PRV along with all of the other bits required for unvented installs.

I did ask him about flow and using the 15mm PRV, but he said it would be fine and so now I'm not sure if I should say anything or not.

In a similar vein, he's also installed a magnaclean into the return pipe to the boiler. The flow and returns are 28mm and run all the way from the boiler room next to the garage to the 2 port valves upstairs in the property. I did ask about this and would have preferred to leave everything at 28mm diameter, but he's fitted a 22mm version. I presume again that this will be a bottle neck in the system?

I've been pretty happy with all of the work he's done, and don't want to start complaining about minor things. But equally, I'm spending a few thousand pounds, and want to ensure that everthing has been done exactly as it should be.

Steve