Will a Pressure Reducing Valve also Reduce Flow Rate?

[Steve]

Hi. This is a bit complicated so please bear with me.

My incoming water pressure is quite high (about 7 bar - just measured it). The info' on the new tap I have says it will handle 5 bar max. - above that, the guarantee isn't valid.

I can currently get about 20 litres/minute flow rate, which, I have read, is the minimum to run a Combi boiler. I want to install one sometime in the future.

If I fit a pressure reducing valve (PRV) on the cold supply now, I can use the tap and also protect the (push-fit) plumbing system from the somewhat high pressure. But - and this is the actual question - will the PRV have the unwanted affect of reducing the flow rate, which could prevent a future Combi from working properly?

And, related to this, are there any PRVs which limit the pressure but not the flow rate too much.

Thanks

Steve

[Tim S]

Hi Steve,

Steve coughed up some electrons that declared:

Tim

It's only worth doing what's practical of course.

There's good odds that could make a noticeable difference. Even if you could kick it up to 25-30l/min, that will be a big improvement over 20.

I like 1/4 turn valves - quick flick and they're operated rather than endless turning :)

No. I had to tunnel under my foundations to do mine - but that was a "must do" job as the old pipe ran up the outside of the house!

None that I really notice. I can tell if the taps on round the back, but I'm not sure if that's pipe wooshing noise or comining from the valve.

It's certainly makes no more noise than one might hear from a bit of exposed pipe under load.

Mine seems to hold the pressure down. Obviously if I adjust it down with the taps off, it holds the higher pressure until you let some water out, but it doesn't appear to creep much over the limit. Static/standing regulation sometimes runs a bit higher than dynamic regulation (same with gas regulators) but it seems fairly close.

I'll have a good look today and let you know later exactly how much it creeps.

Cheers

Tim

[Doctor Drivel]

needs to be secure when turning off and on. Operate valve twice a year off and on to make sure it does not solidify, being 1/4 turn it take 0.5 seconds.

If having a combi or mains pressure water system then always have a 22m full-bore stoptap and a "dedicated" 22m pipe to the combi or cylinder. This ensures the cokbi ger priority if say another cold water tap is turned on.

[Tim S]

Doctor Drivel coughed up some electrons that declared:

My thinking exactly...

I suppose I could have used munsen clips (I have some[1]) screwed onto 10mm chemical wankers set into the brick.

[1] Munsens are an excellent way of hanging your pipe say 50-70mm off a rafter so you can get insulation underneath, as I might indeed do...

Alwys a good idea with any valve that's vaguely important.

Or a better idea - throw the combi in the bin. Horrible things!

Cheers

Tim

[Doctor Drivel]

You know nothing of combi boilers to come out with such a dumb comment. Look at a ~50kW ATAG, 54kW Ethos - quality with flowrates. You can stay in a body-jet shower with these all day and not run out of DHW. They are highly cost effective as you would need expensive 500 litre (minimum) cylinders to do what these can do. The ATAG will deliver 720 litres in 30 minutes and zero time recovery, as it delivers DHW for ever, while the 500 litre cylinder will take over an hour.

W-B 550 (floor mounted).

Any Atmos combi. Vaillant are not bad. Both of these do not have high flowrate models like ATAG.

[Tim S]

Steve coughed up some electrons that declared:

Ok just checked.

Set to exactly 5 bar with tap running slowly.

Turn tap off and it crept up to 5.25bar. So quite a low overshoot.

HTH

Tim

[Tim S]

Doctor Drivel coughed up some electrons that declared:

I don't want to think why *you* would be in the shower all day...

Do they do "Combis Monthly" in a new waterproof and shaggable format now? With a piccy of the model with the oversized ports and the nice tight jets on the cover?

[Doctor Drivel]

Fantastic idea!

[Steve]

Excellent. Many thanks for taking the time/trouble. Steve.

[Steve]

Good idea. I'll definitely try for that. 22mm to combi and 15mm to other stuff. Steve.

[Doctor Drivel]

Where the coldwater line is teed off, near the stoptap, have an in-line restrictor. Then you can throttle down the cold. Have the cold line to the showers off the 22mm line to the combi, just before the combi. Then if a pressure drop around the combi there will be equal pressure to the showers hot & cold.

[Steve]

. Have the cold line to the

Interesting idea. However there will be some extra resistance to flow for the water passing through the combi's heat exchanger.. Also, in my case, there will be a much longer path for the water going through the combi compared to the shower's cold supply.. If the combi and shower cold supplies are both 22m, then the cold would end up at a higher pressure than the hot. The answer is a thermostatic shower!

[Doctor Drivel]

Get the situation. 22mm from stoptap to combi. Tee at stoptap and all cold off this in 15mm. A restrictor on this line, or flow regulator. So you don't want the shower's cold off this cold line, as if a dishwasher kicks in the shower's cold will be robbed and DHW will get too hot, cause a temporary hot blip at the shower which may scald.

The DHW will have a higher resistance than the cold as it runs through the combi. However, some have less resistance than others, and such great issue. Do not have 22mm cold to the shower, only 15mm. When there is a pressure fluctuation around the combi both the DHW and shower cold will be affected and rise up and down pretty well at teh same rate. The mixer must be "combi compatible", with a metal thermostatic strip, not a wax operated cartridge. Best if it has an integral pressure balancing valve, as a combi gives a reasonable stable temperature output.

[Doctor Drivel]

Not an idea, it works, it has been done.