Adjusting the PRV to go to 4 bar..?

[dblvkrb]

We've installed a new 25mm water mains in to replace a led mains in and the pressure is so high we've had to put pressure reducing valve on and cap at 3 bar.

The flowrate from the tap is about 10 litres per minute but we're expecting at least 15l/m. The taps/showers are rated to 3bar but I want to find out if anyone thinks there is a great risk in adjusting the PRV to 4bar to increase the flow.

For info, the combi storage boiler is rated for 18l/m and the current Plumbing has been power flushed, no issues. Any advice appreciated?

 

[dblvkrb]

Is it a shared supply that feeds other houses?

The 25mm pipe goes directly to the mains (someone from the water board did the job). It is not a shared supply.

 

[dblvkrb]

I seem to remember that my kitchen taps have a flow coefficient (Kvs) of something like 0.4 M3/h @ 1 bar which equates to 6.7 LPM @ 1 bar, if the OPs taps are similar then it would require 5 bar to get his expected 15 LPM, his reading of 2.4 bar (one tap) would suggest a flow rate of ~ 10.4 LPM (easy to measure this with a empty milk bottle) the 1.5 bar reading (two taps) would suggest a combined flow rate of ~ 16.4 LPM. The PRV will have its own Kvs which affects flow rate as well plus the differential pressure across it will have a big effect on its output. This Kvs is not known but the manufacturers should certainly know it.
I would suggest (as has been suggested in other posts) increasing the PRV outlet pressure to max with both taps open and then measure both tap flow rates, I would also suggest cleaning the PRV strainer if only to rule it out.
Depending on the above test, to really narrow down the problem I would replace (temporarily) the PRV with a spool piece and repeat the measurements, that will tell a lot IMO.

This is interesting, I thought the indoor tap nozzles would be restricting flow in some manner despite there not being separate flow restrictors in place and I have readings similar to yours on the l/m side. Though I haven't measured it yet, I believe the garden tap is putting out more l/m.

100% agree with you and others who have mentioned I need to test by increasing the pressure or replacing the PRV (or both), hopefully I can get the plumber in this week to talk through and test.

 

[dblvkrb]

Conclusion..

We tested the garden tap and it was putting out >20 l/m, the plumber explained that it is the 12mm flexi pipes that came with the tap sets are restricting the flow a great deal. We tested some of the shower taps with and without the nozzles attached and we measured a difference of about 3-4 l/m (going up to 16 l/m).

That being said the plumbing of the boiler wasn't completely finished, with the blending valve being installed a couple of weeks back. The results are a bit odd. Most of the taps still output at 10-12 l/m, however, the bath taps output at near 20l/m with both taps fully open, the shower output is at 16/m which is certainly good enough for what we need.

I'm not sure why there is such variance but it's worked out for the best, I can only assume it's the type of connections used for each tap combined with the fact that the boiler is now a great deal more efficient now that the blending valve is in. We're still at 4 bar of standing pressure.

 

[John.g]

Conclusion..

We tested the garden tap and it was putting out >20 l/m, the plumber explained that it is the 12mm flexi pipes that came with the tap sets are restricting the flow a great deal. We tested some of the shower taps with and without the nozzles attached and we measured a difference of about 3-4 l/m (going up to 16 l/m).

That being said the plumbing of the boiler wasn't completely finished, with the blending valve being installed a couple of weeks back. The results are a bit odd. Most of the taps still output at 10-12 l/m, however, the bath taps output at near 20l/m with both taps fully open, the shower output is at 16/m which is certainly good enough for what we need.

I'm not sure why there is such variance but it's worked out for the best, I can only assume it's the type of connections used for each tap combined with the fact that the boiler is now a great deal more efficient now that the blending valve is in. We're still at 4 bar of standing pressure.

Shower heads are designed to give a nice spray effect so there is a considerable pressure drop across them so no really big surprises there. You are getting 20 LPM from a bath tap and 10 LPM from the other taps, my bath taps are 3/4", all the remaining taps are ~ 1/2"or even less (metric), my upstairs bath tap flows 12 LPM @ gravity head of 0.25/0.3M, the upstairs bathroom basin tap flows ~ 4 LPM @ the same head.

All in All I think you should be happy enough.

Did you observe the PRV pressure with a flow rate of say 20 LPM?, even assuming a mains PRV upstream pressure of 6/8 bar one would expect a "drooping" in the PRV pressure of (depending on its type & quality) 0.25 bar to 0.5 bar giving 3.75/3.5 bar? @ 20 LPM.

 

[dblvkrb]

Shower heads are designed to give a nice spray effect so there is a considerable pressure drop across them so no really big surprises there. You are getting 20 LPM from a bath tap and 10 LPM from the other taps, my bath taps are 3/4", all the remaining taps are ~ 1/2"or even less (metric), my upstairs bath tap flows 12 LPM @ gravity head of 0.25/0.3M, the upstairs bathroom basin tap flows ~ 4 LPM @ the same head.

All in All I think you should be happy enough.

Did you observe the PRV pressure with a flow rate of say 20 LPM?, even assuming a mains PRV upstream pressure of 6/8 bar one would expect a "drooping" in the PRV pressure of (depending on its type & quality) 0.25 bar to 0.5 bar giving 3.75/3.5 bar? @ 20 LPM.

I haven't read the drop off since my last test - suspect it is going down to ~2bar with 20l/m coming out. The plumber was nervous about going up to 5 bar to test as the fittings are only rated to 3bar. I now see little value in testing an increase in pressure given the l/m had increased where needed.