Megaflow Pressure and Flow Rates

[MLT]

There have been a few variants of the Raindance head (eg one lets air through) & I've fitted a few. They haven't have any restrictor or flow limiter (those things are NOT equivalent, by the way) in them - apart from the mechanism.
I have tested a couple for resistance. They were 20 - 30 litres/min installations, and didn't restrict the flow appreciably. SUggest you test yours., it could be full of crud!

The Ibox housed mixers came/come in (at least) two types. One is a simpler thermostatic mixer, two pipes in, one out, and the other is a two in two out, diverter, which you might use for a bath/shower mixer or a shower and body spray controller.
They both have non return valves in them which are quite small. It helps a bit if you remove them, but not as much as you might hope.
If you have the diverter style mixer, it has a very high internal resistance, much higher than the simpler one. The waterways in there are only about 6mm across in places.


There's been a lot of the usual claptrap in this thread. As Tony says, it all boils down to dynamic pressure, which is the pressure you get when the water is flowing. The only way you're going to know what that is, is to (calculate or) measure it. The pressure drops across every pipe and fitting on the water's way from the road to the shower head.
I'd try removing the non return valves, and I'd try taking the cold to the shower from before the pressure reducing valve. A thermostatic mixer will cope. But if you do both, you're in breach of water regs (possible backflow - though it's highly unlikely),
I'd also add £5 pressure gauges wherever you can.
You do need to measure everything - start with that flow rate.

There's a strainer in the inlet valve group on the Megaflo - you might check it isn't blocked. Also see how wee the non return valve in there is!

Hi Chris
Thanks once again for your constructive comments - just spent tonight taking out the iBox and removing the NRV so will see whether any improvement in the morning but now seen your "bit" above! Also i do have the one with a diverter so note your comments on that possible issue as well, although the Hansgrohe specification does seem to allow this product to go pretty high on both pressure and rate.
When you say the "inlet valve group" is that the PRV as i got the megaflow engineer to leave the old part when it was replaced the other week and noticed there's a NRV in there even. Quite frankly there seems so many NRVs and restrictions all over the place in modern day equipment that however carefull you are planning the pipework the equipment you install to it will get you somewhere!
Cheers.
MLT.

 

[dkleeman]

I have been very tempted to increase the pressure feeding my Megaflo too. I know there are all these dire warnings, and I am not ignoring them. However, removing the pressure reducing valve would seem like madness to me.

The device is tested up to 10 bar and the pressure relief valve is set to 8 bar.

I have been seriously considering replacing the supplied 3/4 inch fixed pressure reducing valve with a 1 inch variable one to see if I can get better shower pressure at, say, 3.5 or 4.0 bar. I wouldn't go above this. We have been very careful with pipe diameters and we have 1 inch supplying the device (which is being restricted by the standard valve).

The shower is 3 m above the Megaflo and has a large rose that outputs over 20 lpm. It has no bite at all at our pressure. The mixer struggles to produce much more than 20 lpm at 2.5 bar (which I am guessing is the effective pressure at the shower). It outputs about 22 lpm without the shower head.

A [much] cheaper alternative would be to fit a smaller shower rose designed to give a 'hard' shower. Does anyone know a good option for this, so that I don't have to blow up my house?

 

[Agile]

DKL, you are mentioning pressures but is that something you have measured?

Have you actually measured the tank pressure when taking 20 li/min?

Tony

 

[dkleeman]

DKL, you are mentioning pressures but is that something you have measured?

Have you actually measured the tank pressure when taking 20 li/min

No I haven't.

 

[Agile]

Thats what is relevant and when you do that you will see why you have a problem.

Tell us and we will make suggestions.

Tony

 

[dkleeman]

I will try to get a pressure gauge fitted.

What I can state already is that I have two identical showers on two floors, one on the same floor as the Megaflo and one 3m above. The are both fed by 22mm pipes to identical valves and identical large 8 inch heads.

Without the heads they pass 26.5 lpm on floor one and 21.5 lpm on floor two (above).

Generally speaking, the showers are not affected by water draw-off in other parts of the house.

Daniel

 

[MLT]

I have been seriously considering replacing the supplied 3/4 inch fixed pressure reducing valve with a 1 inch variable one to see if I can get better shower pressure at, say, 3.5 or 4.0 bar. I wouldn't go above this. We have been very careful with pipe diameters and we have 1 inch supplying the device (which is being restricted by the standard valve).
[/quote]
dkleeman
Did you ever replace the pressure reducing valve with a 1" variable one and set at 4 bar? Exactly what i have been thinking of doing and in fact have seen the same done in Germany with great showering results!

 

[dkleeman]

Did you ever replace the pressure reducing valve with a 1" variable one and set at 4 bar? Exactly what i have been thinking of doing and in fact have seen the same done in Germany with great showering results!

Well, I fitted a pressure gauge and found that the mains pressure did not go above 2 bar - so we did not proceed with changing the PRV. We did change the routing so that the cold was teed off before the Megaflo PRV and this maybe helped overall flow rates.

 

[mysteryman]

I am surprised that no-one has pointed out that the shower cold feed should be taken from the balanced pressure cold offtake on the unvented safety kit. This is exactly what it is for. Many guys who should know better don't seem to comprehend this at all.

Further, as all these alterations have been done, you may have the above mentioned 'crud' in the pipework, due to things being disturbed.

Many of the regulations re unvented cylinders are grossly overdone - the regulatory body is basically a manufacturers' cartel. This is especially so in the nonsense about 2 port valves in the cylinder primaries - but that's not relevant here!

 

[gordonspants]

If the shower is as flat as a fart the dynamic pressure is dropping either because your shower is just too high-flow and german for a UK-spec 3 bar megaflo with a prv on it, or because something somewhere is faulty/blocked - your stoptap is wide open isn't it?
Gauges as recommended above will help figure out what's going on.
I can shut our 250l accumulator off, and put our shower and bath on full to drop the pressure gauge on the mains to virtually nothing - the flow then becomes a trickle as the mains simply can't cope.
Indicated pressure can go as low as half a bar.
We have a decent 3 to 4 bar and 15mm mains pipe here - but that's static figures.
One possible option might be an accumulator as we've done?
Stick a big 300-500l one just upstream of an unvented cylinder and you should be laughing, even with a rubbish low flow PRV.

 

[MLT]

Right then, i started this so here's my person update! In the quest for a decent shower i searched for a variable PRV that had less restriction that the one which comes with a megaflow as standard and came up with a Reliance 520-467-0802 which can be set at a max of 5 bar from www.advancewater.co.uk. Incidently Reliance manufacture the one that comes as standard. I knew my mains pressure was 4.2 bar and wanted to see if this set at 4 bar made any great difference. I spoke to megaflow technical desk themselves and explained what i planned and why, whilst asking specifically whether what i proposed was dangerous at all. They categorically stated that whilst they could not advise replacing with this as it invalidates their warranty they confirmed replacing with this PRV set at 4 bar was in NO WAY dangerous due to other built in safety features of the megaflow, they said the worse that could happen was a bit of water through the discharge pipe in exceptional circumstances. Given my alternative was to rip the thing out and replace with a traditional system with booster pumps which would have probably cost a few grand, invalidating their warranty was not a concern and having had the safety aspect confirmed the work was carried out. Wow what a difference, the showers now pump out 4 bar not 2.8 bar, the flow rates have increased by 30% to about 24l/min and we have showers that are awesome. On top of that 4 weeks later and not a drop out of the discharge pipe.
No doubt i'll get flack from certain members of the forum, but this works and for the sake of about £80 for the new PRV and an hour labour it's the best money i've spent on the whole system. Best. Mark.

 

[Agile]

A static mains pressure of 4.2 Bar is only one aspect.

The important one is what the dynamic pressure! Thats the pressure at the inlet to the cylinder when teking 24 li/min.

With a Megaflow there is a built in air bubble at the top which gives an accumulator action which boosts flow rate for the first few minutes but all serious calculations and assessments would be done on the dynamic situation when the flow rate has stabilised.

Tony