Upgrading pipe sizes

[fezster]

If you are getting 1 bar working pressure on the ground floor the pressure on the upper floors is going to be less than this, so yes the working pressure could be a factor.

It's also possible that it could be a combination of factors such as pipe sizing and working pressure.

See post #19. Static pressure is 2.5 bar (0.5 bar drop for 5m in height presumably), and working pressure with one shower running at 18 l/m is 2.1 bar.

 

[Scott_D]

Have you tried with the softener bypass open?

 

[Pro Action]

Is there a gate valve after the pressure relief valve?
If so that shouldn't be there, get a G3 certified plumber to remove that.

 

[fezster]

Have you tried with the softener bypass open?

Yup. Exactly the same. Softener is a Tapworks AD11 with high flow kit, so *should* be capable of 54 l/m.

 

[fezster]

Is there a gate valve after the pressure relief valve?
If so that shouldn't be there, get a G3 certified plumber to remove that.

There is. That's interesting advice - could you tell me why it shouldn't be there? And would it be causing the flow issues, or do you mean it shouldnt be there from a safety point of view? (It was the original G3 certified installer who put it there btw).

One other thing which occurred to me. I was reading the installation guide for various Reliance pressure reducing valves. They advise a minimum distance between IT and the balanced cold water take off. The instructions say this is to ensure "laminar flow". The megaflo instructions have no such advice. I wonder if my balanced cold should be slightly further away from the prv.

Edit - I see it's in the megaflo MI:

vii) No valve should be fitted between the 8 bar pressure relief valve and the Megaflo eco unit.

I wonder what the reason is though.

 

[fezster]

Thinking about it logically, it's in case the gate valve is closed shut if the cylinder were to rise in pressure uncontrollably and if the T&P relief valve were to fail. Useful to know and will have it removed, but doubt it's the cause of my problem.

 

[ShaunCorbs]

Thinking about it logically, it's in case the gate valve is closed shut if the cylinder were to rise in pressure uncontrollably and if the T&P relief valve were to fail. Useful to know and will have it removed, but doubt it's the cause of my problem.

Look at it again think it's just for draining down

 

[Staffy85]

Drops to 1 bar with 50 l/m flowing. I don't pretend to fully understand working pressure, but I think those are pretty good figures for multiple outlets.

pressure and flow rate are two separate things as you probably know but also work together hand in hand, {your problem is showers not great when more then 1 is in use } , my theory is showers can be {they are} restrictive depending on the make/model some are more suited to unvented supplys rather then gravity fed {i.e more restrictive so not ideal for pressures under 1bar} , max/min pressures are stated with all showers in there manual , flow rate isn't your problem as it seems you have plenty of water readily available, if you have a restriction i.e a shower then you need a force {pressure} to force the water through to get a better flow at the shower oulet. the way I see it is that if your incoming main was 5bar not 4 then it would drop down to 2bar and not 1bar which would mean they would be twice as good!...

 

[fezster]

pressure and flow rate are two separate things as you probably know but also work together hand in hand, {your problem is showers not great when more then 1 is in use } , .

I agree with all you've said, except I've attached a gauge to the shower with one other shower running. It read 2.1 bar. Static was 2.5 bar. I.e. a 0.4 bar drop with 18 l/m flowing.

The one thing which is ringing alarm bells for me is the drain off valve just before the megaflo (see my last picture). It is able to deliver 28 l/m. Ignoring the fact it isn't delivering more (I'd expect it to match the outside tap before the PRV), what is surprising is that if I run any other outlet after the PRV, it reduces in flow so that the total of the 2 outlets delivers 28 l/m. And with 3 outlets, again they total 28 l/m.

This says to me the flow rate after my PRV (pressure reducing valve) is restricted to 28 l/m. I found an old thread on diynot where somebody had the same problem (and the same 28 l/m restriction):

Megaflow Pressure and Flow Rates | Page 4 | DIYnot Forums

I wonder whether the megaflo PRV just isnt capable of higher flow rates. I'd be interested to hear if anybody has witnessed themselves to say otherwise.

 

[fezster]

Update on this for the benefit of others. Increased the pipe size attached to the 32mm incoming main from 22mm to 28mm. And increased the megaflo output to 28mm as well as the balanced cold, for approximately 2-3 metres - whatever was accessible in the garage.

This has made all the difference. A single shower feels much better, but more importantly, even with all 3 showers running, they are all extremely good. I wouldnt say there is no drop off in performance, as there is. But it's not as dramatic and because performance has increased anyway, the drop is now on par (or better) than what I was getting with just one shower previously.

A few notes which are important:

1. I have a 22mm/ 3/4" bsp water softener sitting in between the 28mm pipework at the start. To put paid to the myth that there is no benefit to increasing pipe size downstream.

2. My gut feeling is that the 28mm pressure reducing valve has had a big impact on performance. Looking at the haetre sadia 22mm one, the orifice is tiny - how they claim to get 70 l/m through that, I don't know.

Hope this helps someone else.