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Adjusting the PRV to go to 4 bar..?
- Thread starter dblvkrb
- Start date
What would you test first? If it isn't the PRV what do you think the issue is? The pipes were tested and cleaned prior to installation.
Just want to add that the picture uploaded was about a month ago and probably was mid installation, but I am definitely going to double check it (and take some more pics).
A
Aire
A
Aire
Take a picture of the stop tap and pressure reducing valve.
A
Aire
To be honest, I know we're going off track here but the whole system seems pointless to me, why run cold mains through heat recovery, then through a heat store only to blend it down to 30°. Why not just have the heat recovery?
Sorry im with you it’s a set ok that makes more sense but my argument still remains. I’m not arguing with the logic of what you’re saying but that still looks like it’s piped in 22 under the boiler for cold and dhw and op has said it comes in in 15mm so obviously it upsized too which is going to further affect flow
A
Aire
Hard to tell, the shock arrestor under the boiler looks to me like it's piped on a 15mm supply.
A
Aire
Haha, nope. That we can agree on 😉
Personally I think the install is a bit untidy the flow rate could be improved on by correct pipe sizing is there a dedicated supply straight from the incoming stopcock purely supplying the cold water inlet to the gas saver 22mm minimum without anything else coming off it? there will be Pressure loss as water passes through each piece of equipment and height and length of the pipework needs to be considered. Kop
I will double check and hopefully take some more pictures, but I think it's 15mm supply in for the cold water inlet. Thanks all for your advice so far - very useful.
I'm surprised by some of the responses relating to pressure and flow rate.
The pipe diameter and length determine the pressure loss in the pipe run. If you have a longer pipe (you can try this with a garden hose reel), the pressure loss will be greater and you will get less flow at the end. If you increase the pipe diameter, the pressure loss will be less and you will get more flow (EDIT to clarify - "more" than the previous example - you can't get more out than you put in!).
Given you will have a loss of pressure along the pipe run, if you increase the pressure you start with, the resulting working pressure (i.e. with water flowing) will be higher too. Therefore, increasing the pressure on the PRV (assuming your incoming pressure is sufficient) will indeed result in a higher flow rate.
I do agree that the more correct approach would be to size the pipes adequately in the first place. You also need to ensure that the pressure is sufficiently reduced to avoid damage to components (eg. some thermostatic showers are designed to work at 3 bar).
The pipe diameter and length determine the pressure loss in the pipe run. If you have a longer pipe (you can try this with a garden hose reel), the pressure loss will be greater and you will get less flow at the end. If you increase the pipe diameter, the pressure loss will be less and you will get more flow (EDIT to clarify - "more" than the previous example - you can't get more out than you put in!).
Given you will have a loss of pressure along the pipe run, if you increase the pressure you start with, the resulting working pressure (i.e. with water flowing) will be higher too. Therefore, increasing the pressure on the PRV (assuming your incoming pressure is sufficient) will indeed result in a higher flow rate.
I do agree that the more correct approach would be to size the pipes adequately in the first place. You also need to ensure that the pressure is sufficiently reduced to avoid damage to components (eg. some thermostatic showers are designed to work at 3 bar).
W
Welder
Can someone please explain to me why plumbers do not understand how flow is a consquence of pressure & bore? Keep the bore the same & increase the pressure & flow increases. Similarly, increase the bore & keep. Pressure the same & flow increases.
The point of a pressure reducing valve is to provide a maximum pressure with 'unduly' limiting flow. All PRVs impeed flow somewhat.
In terms of increasing flow in this instance 'bouncing out of the sink' is zero indication of anything. The only real test is a weir gauge or physically timed test. The real test is looking at the flow rate of a second outlet.
I hope this basic information helps people.
The point of a pressure reducing valve is to provide a maximum pressure with 'unduly' limiting flow. All PRVs impeed flow somewhat.
In terms of increasing flow in this instance 'bouncing out of the sink' is zero indication of anything. The only real test is a weir gauge or physically timed test. The real test is looking at the flow rate of a second outlet.
I hope this basic information helps people.
Last edited by a moderator:
Rob Foster
Esteemed
I agree this is the most worrying aspect of this idea
Centralheatking
Rob Foster
Esteemed
Pressure and volume are obviously inter related but in actual fact separate issues , in fact Yorkshire Dave if you pm me we could produce a simple fact sheet to clear up,this issue
Once and for all ...ok ?
Centralheatking
Increasing the pressure will certainly increase flow rate as it is proportional to the sq.root of pressure, if the pressure is increased to 4 bar at the tap (by adjusting the pressure reducing valve) then the flow rate should theoretically increase by a factor of (4/3)^0.5 = 1.15 so the flow rate should increase from 10 to 11.5 lpm.....that is assuming there is 3 bar at the tap when it was flowing 10 lpm originally, in practice pipe friction losses will reduce this.
W
Welder
Personally, I'd be ensuring all valves are fully open and no undue or inadvertant restrictions are being applied to throttle flow before messing with what are specific design settings.
All NVQ-qualified plumbers understand (or once understood!) these ideas, which are part of the Level 1 one curriculum, e.g.:
https://bpec.org.uk/wp-content/uplo...2-and-L3-Plumbing-and-Heating-Diploma-v23.pdf
One problem is that not everybody who does plumbing is a qualified plumber. Also, customers use 'water pressure' in a colloquial, not a technical sense. When lay-persons talk about water pressure they are usually referring to the properties of the jet formed at outlets and how the jet and flow respond to small changes in the control rather than what's going on inside the pipework.
Update:
Ok so I've taken a picture of the PRV (attached), the pipe from the stopcock is definitely 22mm, not 15mm, my bad.
I couldn't get to the boiler today as the house is a building site at the moment and the garage (where the boiler is located) is all boarded up. That being said I could see the the pipes are all housed now, so I suspect the blending valve is fitted but I will check next week.
The boiler is rated to 5 bar, but I was thinking of testing the pressure at each of the taps using a gauge, before testing to see if there if is an increase in flow rate when going up in .5 increments (pressure) each time.
Thoughts?
Ok so I've taken a picture of the PRV (attached), the pipe from the stopcock is definitely 22mm, not 15mm, my bad.
I couldn't get to the boiler today as the house is a building site at the moment and the garage (where the boiler is located) is all boarded up. That being said I could see the the pipes are all housed now, so I suspect the blending valve is fitted but I will check next week.
The boiler is rated to 5 bar, but I was thinking of testing the pressure at each of the taps using a gauge, before testing to see if there if is an increase in flow rate when going up in .5 increments (pressure) each time.
Thoughts?
Run the tap at 10l/min and then check the pressure guage
Then at 5l/min and check the pressure guage
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