Adjusting the PRV to go to 4 bar..?

[Riley]

Honest opinion I’d be tempted to change the PRV

 

[dblvkrb]

Yes boiler pic

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

 

[dblvkrb]

It's a newly installed 25mm main as I mentioned in my original post, I meant 15mm pipe running from the stopcock.

Also completely forgot make of PRV, will check though.

 

[dblvkrb]

As Riley and others have said pressure and flow are not the same thing. A PRV could have sorted out the splashing tap but will not have affected flow.

As an example:

If we have two taps both with a flow rate of 15 lpm where tap no1 has 6bar pressure and tap no2 has 3 bar pressure, both will fill the sink up in the same amount of time. But when taps are turned on tap no1 will splash much more violently off the surface of the sink due to the much greater pressure than tap no2. i.e. its the same amount of water but coming out with more force, turn the pressure down and water hits the sink with less force so doesn't splash/bounce but its exact same amount of water per minute hitting the sink.

I understand this, and I'll caveat by saying I didn't personally test the flow rate before the PRV installation but it's obvious it has reduced both the flow rate and the pressure. I'm guessing where we may be getting to is possibly a defective/clogged PRV?

 

[Aire]

As much as i appreciate why everyone is saying increasing the pressure of the prv won't do anything, turning it up and seeing if it improves isn't going to hurt, even by half a bar, the boiler is rated up to 5bar anyway so it's not going to hurt. And if it doesn't work atleast you've ruled it out.

 

[rpm]

Seen 6bar static pressure reduce to 0.6bar dynamic pressure along with the sort of flow you would expect from 0.6bar.

 

[rpm]

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

View attachment 36032

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

View attachment 36032

Not the greatest pic, but hopefully gives you an idea of the boiler - the hot flow is only 2 l/m less than off the cold mains, I doubt it is the issue.

View attachment 36032

Those valves supposed to be closed guys?

 

[dblvkrb]

Those valves supposed to be closed guys?

So.. I could test increasing the static (PRV) pressure to see if the dynamic pressure improves the flow, have I understood this right?

I'll pass on whether the valves should be closed (I did not install the boiler) - but it is working as expected and the hot flow is similar to the cold mains flow.

 

[Aire]

Yes you can increase the pressure, as I said your boiler is rated at 5 bar, stick below that and you'll be fine.

And no those valves aren't supposed to be closed, but then the hot feed coming from the top of the heat store should also feed the boiler through a blending valve mixed with the cold main. Whoever installed the boiler hasn't finished it.

 

[Riley]

If that’s a heat store then what pressure is that safe up to??

 

[dblvkrb]

Yes you can increase the pressure, as I said your boiler is rated at 5 bar, stick below that and you'll be fine.

And no those valves aren't supposed to be closed, but then the hot feed coming from the top of the heat store should also feed the boiler through a blending valve mixed with the cold main. Whoever installed the boiler hasn't finished it.

Thanks - I will definitely check out the boiler setup with the installer, the blending valve should be somewhere. The boiler is rated to 5 bar, just worried about the taps being rated to 3, but I think I may have to test this anyway to see exactly how much the flow rate is effected.

 

[Riley]

Dear lord why risk leaks and damage swap out the prv also what is the cold inlet pipe size to the hot water Store.

 

[Riley]

My suspicion is it’s a piping issue exacerbated by the restriction of a prv

 

[Riley]

Seriously though test it in various places you’re plunging straight in with what isn’t the answer and will not be told

 

[Aire]

If that’s a heat store then what pressure is that safe up to??

It's rated upto 5 bar, the boiler, flue gas recovery and heat store all come together. The heat store is pressurised by the heating water not the mains, it has a coil going through it which comes off the flue gas and back into the cold feed to the boiler, at least it should do but as I said, it's not finished. And I just want to point out to you again that I don't disagree with anything your saying and op has gone the wrong way about reducing his flow rate but for the sake of adjusting the pressure and how long it will take it's worth a try.

 

[Riley]

But it’s not answering the issue it’s a bodge

 

[Riley]

So what feeds the store??? Surely it’s mains water?

 

[dblvkrb]

Seriously though test it in various places you’re plunging straight in with what isn’t the answer and will not be told

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.

 

[dblvkrb]

It's rated upto 5 bar, the boiler, flue gas recovery and heat store all come together. The heat store is pressurised by the heating water not the mains, it has a coil going through it which comes off the flue gas and back into the cold feed to the boiler, at least it should do but as I said, it's not finished. And I just want to point out to you again that I don't disagree with anything your saying and op has gone the wrong way about reducing his flow rate but for the sake of adjusting the pressure and how long it will take it's worth a try.

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).

 

[Aire]

So what feeds the store??? Surely it’s mains water?

 

[Aire]

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.

Take a picture of the stop tap and pressure reducing valve.

 

[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?

 

[Riley]

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

 

[Aire]

Hard to tell, the shock arrestor under the boiler looks to me like it's piped on a 15mm supply.

 

[Riley]

Not the tidiest install is it 🙂

 

[Aire]

Not the tidiest install is it 🙂

Haha, nope. That we can agree on 😉

 

[king of pipes]

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

 

[dblvkrb]

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.

 

[fezster]

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).

 

[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.

 

[Rob Foster]

Also going above 3bar can impact other things such as the boiler from a safety perspective

I agree this is the most worrying aspect of this idea
Centralheatking

 

[Rob Foster]

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.

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

 

[John.g]

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.

Pressure and flow are two different things, upping the pressure reducer to 4bar will likely have no impact on the flow rate.

 

[Welder]

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.

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.

 

[Riley]

I just think they need to get a plumber in that understands system design to test all facets correctly