Pressure Reducing Valves for UVC

[Spinny]

I mentioned on another topic, plumber is planning to replace my Caleffi pressure reducing combination valve with a 28mm valve to improve flow (my pipework is 22mm).

 

I am reading some stuff about pressure reducing valves having to be sized correctly for expected flows, and sometimes 2 valves plumbed in parallel may be required - one for low flow, one for higher flow.

(I guess I expect flows from say 5/6 l/m with one tap on through to say 35-40 l/m - 2 showers, couple of taps, kitchen appliance all going.)

(Seems unfortunate that someone can't design a pressure reducing valve that works well without restricting flow over a wide flow range)

 

PS Do you actually need to have a balanced cold ?

 

What experience and advice can people offer re combination valves for domestic UVC systems and maximising flow ?

[JohnMo]

1 hour ago, Spinny said:

pipework is 22mm

Why that big?

 

1 hour ago, Spinny said:

guess I expect flows from say 5/6 l/m with one tap on through to say 35-40 l/m - 2 showers, couple of taps, kitchen appliance all going

But when is that likely to ever happen. If you hot water is above 40 degs, you will be adding cold water to flow of the showers as well... Think you may be loosing the plot!

[SimonD]

1 hour ago, Spinny said:

I mentioned on another topic, plumber is planning to replace my Caleffi pressure reducing combination valve with a 28mm valve to improve flow (my pipework is 22mm).

 

I am reading some stuff about pressure reducing valves having to be sized correctly for expected flows, and sometimes 2 valves plumbed in parallel may be required - one for low flow, one for higher flow.

(I guess I expect flows from say 5/6 l/m with one tap on through to say 35-40 l/m - 2 showers, couple of taps, kitchen appliance all going.)

(Seems unfortunate that someone can't design a pressure reducing valve that works well without restricting flow over a wide flow range)

 

PS Do you actually need to have a balanced cold ?

 

What experience and advice can people offer re combination valves for domestic UVC systems and maximising flow ?

 

I don't think you'll see any difference whatsoever by upgrading the multi-bloc (inlet group) - which I presume is what you're referring to? -  to 28mm. By far the best solution if you don't have sufficient flow rates it to upgrade/modify your supply pipework - and we know you've got some design issues there. My experience is that the multi-bloc units cope absolutely fine with anything from 6l/m to 30l/m. Where I am, I don't see any supply rates much above 30l/m from the mains. Some of these have regulators that provide the same pressure whether there's flow or not. 

If you're replacing the multi-bloc, you need to make sure the pressure relief valve has the same pressure specification as the manufacturer supplied unit - e.g. 4.5bar or 6bar

 

You should use the balanced cold for any mixed outlets because imbalance in pressure can cause problems in these fitting - e.g. where I am mains pressure can easily be 6bar so if you don't balance this you have 6bar at one side and 3 bar at the other. I always install and use the balanced cold as otherwise I'm installing another prv after the stockcock.

[Spinny]

3 hours ago, JohnMo said:

But when is that likely to ever happen. If you hot water is above 40 degs, you will be adding cold water to flow of the showers as well... Think you may be loosing the plot!

I am talking total combined output there - that is Hot Flow + Cold Flow.

If it is Christmas and I have family staying - say every year for the next 15 years. Then you have  6 adults in the house, maybe 2 or 3 grandchildren. You want to run 2 showers at the same time. Someone is running taps in the kitchen making breakfast, someone just put the washer on, and someone flushes the loo. So if the system can't handle it, someone is getting a bad shower, and you are into shouting round the house about who can use a bathroom or ensuite.

 

At present the highest simultaneous output I am getting is 34 l/m combined hot and cold downstairs - that is 17 l/m each for hot and cold. Hot flow and cold flow are not separate, they all come through one input pipe and combination valve. I am only getting more like 20-24 l/m simultaneous combined on other outlets.

 

I don't think this is unusual, part of the selling point of UVC vs gravity fed is the ability to run two bathrooms etc. My mains supply should be capable of 40 l/m+. Are we really saying there is no-one here that has ever seen flow problems with a domestic system regardless of how it is plumbed.

[SimonD]

12 minutes ago, Spinny said:

Are we really saying there is no-one here that has ever seen flow problems with a domestic system regardless of how it is plumbed.

 

I see them and fix them all the time. Like I said above, it's unlikely your multi-bloc, but the supply pipework to the uvc that's the problem.

[Nickfromwales]

Adding a cold mains accumulator will make a huge difference, for stabilising what you have.

 

Or….

2 hours ago, SimonD said:

 

I see them and fix them all the time. Like I said above, it's unlikely your multi-bloc, but the supply pipework to the uvc that's the problem.…

…this.

 

Having small bore pipework between the stopcock and the UVC control group is very impactful on performance, but so many plumbers ignore this; probably some just don't realise it is of such importance.

 

Adding an accumulator can be quick and simple, if you have space for one, and guarantees results. I’ve fitted loads over the last 20+ years and always had great results.

 

Beefing up the control group from 22 - 28mm won’t do much tbh, and I've had lots of UVC’s on 22mm that will do 2 showers simultaneously, where the property has a very good incoming cold mains, so I also doubt that is worth the investment. 
 

As always these things are hard to comment on without being able to see the system and survey it properly. 

[Spinny]

OK thanks for comments.

The supply pipework is 32mm MDPE mains in, connected into 22mm copper (16mm MLCP tee to kitchen, 15mm copper tee to outside tap) through water softener (currently on bypass), then approx 5m of 25mm MLCP pipe to the cylinder location, final 1m in 22mm copper to the reducing combination valve.

 

I was getting 37 l/m from the outside tap, so I know the mains supply is capable of providing a continuous 37l/m through 15mm copper. So the main supply through the 22mm copper and 25mm MLCP should be providing at least that and one would think 40l/m + into the combination valve. Mains pressure 3.5 bar.

 

Unfortunately I can't change the 5m of 25mm MLCP with its press fit connector at each end, because it runs under the suspended floor which now has underfloor heating installed. Had I seen the MLCP connector bore reduction at the time I would have insisted the plumber put in 32mm MLCP. But that is the big unspeakable secret with MLCP and press fittings.

 

I have seen some Wavin Tigris M5 / K5 press fit MLCP connectors which claim ''The new Wavin Tigris K5/M5 with Opti Flow reduces the pressure loss in the installation due to the up to 50% larger orifice..''. Mentioned them to my plumber who promptly claimed they would make no difference, and proceeded to fit cheaper ones he uses.

 

A lot of trade are not interested in using anything except what is available off the shelf at their chosen merchant. System performance for the customer doesn't come into it - in fact I have never seen a plumber measure a flow rate.