Megaflow Pressure and Flow Rates

[MLT]

Dear All
Having read numerous threads and advice all over the internet on this I thought I'd join this site as it appears the most informative and start my own one.
Had a megaflow installed during our house refurb as the shower we were able to get from an approx 15 year old floor mounted Worcester combi was awesome (other than if another tap was turned on or toilet flushed etc) so (sadly) assumed it would be just as good from a megaflow which in addition might also allow a shower not to be affected as badly by another outlet being opened.
The old pipework was a hotch potch of lead and 15mm copper with knackered old valve taps dotted around when we used to get a pounding shower from the combi. This was replaced by new bigger bore (22 or 25mm?) pipe from the main in the road the whole way into the house with only 4 x 90 degree bends before it gets to the megaflow on the 1st floor.
Pressure going in is 4 bar+ and flow rate 40 l/min (as measured in front of me by Thames Water both inside and outside the house when it was the old pipework.
Result now = showers nowhere near as good as the old system. Had it all checked by a different plumber to that who installed who reckons we've got 2.8 bar and only 28 l/min coming out the megaflow which is then 2.5 bar and 22 l/min once the other side of the 2 shower mixers.
Sadly i never measured the pressure or flow rate at the shower on the old system.
Needless to say at present i am not happy with the pressure not flow rate and I can not understand why the Megaflow reduces the pressure to 3 bar when many shower products on the market today require 3 bar minimum to work well (Hansgrohe). Having done too much research after the event I now wish I'd done a traditional system with HWT in the loft and stuck a couple of 4 bar monsoon pumps up there but i am where i am now and need to make the most of what I've got.
The pressure reducing valve (PRV) needed started to leak about 6 months after installation. So I relayed the above to the plumber i had to come and fix it who suggested I have the PRV removed and replace it with a double check valve which I pressume would mean I'd get back to benefiting from the full 4 bar+ and having seen the huge restriction inside the PRV water has to pass through perhaps the flow rate would significantly improve. I also noticed inside the PRV there is a non return valve - I was thinking in the first instance just removing that might improve the flow rate somewhat.
Has anyone else heard of removing the PRV on one of these? Given the thing has an 8 bar expansion relief valve for safety, I can't see any major reason not to give it a go other than invalidating the guarantee which quite frankly given I think it's a pretty useless bit of kit wouldn't concern me!
Any advice and suggestions will be greatly received.
Thanks in advance.
MT.

 

[doitall]

No, you cannot remove the combination valve or the PRV without putting lives at risk

If the megaflow can't better the Wb then there's a fault with it.

I assume the WB was a Heatslave.

 

[MLT]

Thanks for the speedy reply. I was led to believe that the PRV set at 3 bar was a level set by megaflow in case pipework was questionable, nothing to do with safety and it was the expansion relief valve which was the safety valve set at 6 or 8 bar for the pressurised cylender? In which case why would removing the PRV put lives at risk?
Further question - apparently the PRV is different in mainland Europe - anyone know - ie is it set at higher than 3 bar? It just seems stupid in hindsight that the megaflow reduces 4 bar down to 3 bar and knocks over 30% off the flow rate?
I can't remember re the WB model - but do know that the shower was much better with it than the megaflow! It was big, sat on the floor and had a little HW tank inside it. Could it have been that the old WB let the full 4 bar come through and also didn't reduce the flow rate by as much as the megaflow seems to?
Thanks again.

 

[doitall]

For a starter we ain't in mainland Europe.

The megaflow is an Wras approved design as is all unvented cylinders for use in this country.

The combination valve is an essential component towards the overall safety of the cylinder and the occupants.

The boiler was able to deliver around 20Ltrs/m the Megaflow should be around 30Ltr/m assuming the mains can deliver it, in addition to any cold.

Have you change the shower, are the filters and rose clean, etc. How big is the rose.

With the right fittings you should have a shower that hurts when you stand under it.

 

[powell30]

I agree.....the megaflow should easily outperform the WB

You must have set up issues. Oh and 2.5bar shower and 22l per minute is good. Perhaps the system is set up incorrectly.

Don't under any circumstances remove the prv/combi valve. Dangerous and will invalidate your warranty

 

[doitall]

Don't under any circumstances remove the prv/combi valve. Dangerous and will invalidate your warranty

And your house and any other insurance.

 

[mickyg]

and possibly put you in contention for a darwin award

set up issues. 40/l min and 4bar+ at inlet to property, no reason why you shouldn't achieve a very painful shower

 

[ianniann]

Nobody has asked the important question. Do you understand the difference between pressure and flow rate? 2.5 bar and 22l/min is a good shower by any standards, assuming that is actually what is coming out of the shower. Of course that is a big assumption and you should at the very least measure the flow rate yourself into a bucket.

Even a big storage combi, which I assume you had before, would struggle to put out 22l/min of water at shower temperature, but it could easily have given a pressure of more than 2.5 bar (mixed with cold). In fact it would could well have been close to your 4 bar mains pressure. Since most shower heads won't let 22l of water through anyway, you may now be getting a similar flow rate to before and a lower pressure, which would give you a worse shower experience.

In addition to checkout the flow rate, it might be helpful to give a little more information about the shower head. Heads? The numbers you have described coming through a single off-the-shelf head would be too much for most people.

 

[MLT]

Dear Do It All
"For a starter we ain't in mainland Europe" - thanks for pointing that out. Whilst off subject there are many things in the UK woefully under specified compared to Europe and the rest of the world which doesn't necessarily mean the UK specification is best and it would merely be interesting to ascertain what the specification is on mainland Europe in order to compare to over here rather than have a Geography lesson! Nothwithstanding, if you do wish to continue to discuss my take on a megaflow then here we go:-
"Have you change the shower, are the filters and rose clean, etc. How big is the rose" - yes we have changed it but not before using the previous shower mixer and head on the new megaflow so I was previously comparing like with like although now we do have a new mixer and bigger head (with all filters and the like checked). If the boiler was previously delivering 20 l/min and I know we are now at more than that from the megaflow then what's your take on my theory "Could it have been that the old WB let the full 4 bar come through" whereas the megaflow reduces this to 2.8-3 bar? This would imply my issue is the pressure not flow rate? In which case i would restate "I now wish I'd done a traditional system with HWT in the loft and stuck a couple of 4 bar monsoon pumps up there" as IMHO a megaflow is simply over rated.
"With the right fittings you should have a shower that hurts when you stand under it" - this is what we used to have and could not turn the mixer onto full - if only that were the same now!
Dear powell30
"You must have set up issues. Perhaps the system is set up incorrectly."
The system is balanced and 22 mm pipework is run all the way to the shower mixers with as few bends as possible. As it's the same at both showers it can't be that there's a blockage in pipework causing resistance - what else would you describe as set up issues / set up incorrectly please?
"Oh and 2.5bar shower and 22l per minute is good" - as per my 1st posting, is 2.5 bar good when a lot of modern day kit actually needs 3 bar? As above, on a personal level I am bitterly disappointed with the megaflow system and wish we'd done a traditional system with a pump to each showers - hindsight what a wonderful world!
Now just trying to make the most of what we've got to see where i can get to.
Thanks very much in anticipation of your responses.
MT.

 

[electronicsuk]

Pressure going in is 4 bar+ and flow rate 40 l/min (as measured in front of me by Thames Water both inside and outside the house when it was the old pipework.

OK, now you've got me confused. You had 4 bar and 40l/min cold mains incoming with the old pipework. Since you had the new supply installed to the street, what flow rate do you get now directly from the cold mains, completely ignoring the megaflow?

 

[MLT]

Hi IannIann
Thanks for your reply which I think has now got to the crux of the matter. As per my initial posting:- "Had it all checked by a different plumber to that who installed who reckons we've got 2.8 bar and only 28 l/min coming out the megaflow which is then 2.5 bar and 22 l/min once the other side of the 2 shower mixers."
As per my 2nd posting "Could it have been that the old WB let the full 4 bar come through and also didn't reduce the flow rate by as much as the megaflow seems to?"
Which is what you indicate is more likely the issue I now have being you state "you may now be getting a similar flow rate to before and a lower pressure, which would give you a worse shower experience."
This is why it all started with me asking:- "the plumber i had to come and fix it who suggested I have the PRV removed and replace it with a double check valve which I presume would mean I'd get back to benefiting from the full 4 bar+ and having seen the huge restriction inside the PRV water has to pass through perhaps the flow rate would significantly improve. I also noticed inside the PRV there is a non return valve - I was thinking in the first instance just removing that might improve the flow rate somewhat.
Has anyone else heard of removing the PRV on one of these? Given the thing has an 8 bar expansion relief valve for safety, I can't see any major reason not to give it a go other than invalidating the guarantee which quite frankly given I think it's a pretty useless bit of kit wouldn't concern me!"
But all I've had to date is being told I'll kill people and invalidate my house insurance in the process despite not suggesting I touch the 8 bar expansion relief valve - any views Iann?
Cheers.
MT.

 

[electronicsuk]

Has anyone else heard of removing the PRV on one of these? Given the thing has an 8 bar expansion relief valve for safety, I can't see any major reason not to give it a go other than invalidating the guarantee which quite frankly given I think it's a pretty useless bit of kit wouldn't concern me!"
But all I've had to date is being told I'll kill people and invalidate my house insurance in the process despite not suggesting I touch the 8 bar expansion relief valve - any views Iann?
Cheers.
MT.

I'm sorry it's not what you want to hear, but you must not remove the PRV. If you proceed to do so, it will have been completely pointless having had the cylinder installed by a G3 certified plumber as the installation will no longer be compliant. If the cylinder is designed, tested and instructed to be installed with a PRV upfront on the incoming cold supply, then you must fit one. No plumber worth their salt is going to recommend you remove or bypass it.

 

[MLT]

Pressure going in is 4 bar+ and flow rate 40 l/min (as measured in front of me by Thames Water both inside and outside the house when it was the old pipework.

OK, now you've got me confused. You had 4 bar and 40l/min cold mains incoming with the old pipework. Since you had the new supply installed to the street, what flow rate do you get now directly from the cold mains, completely ignoring the megaflow?

To be exact Thames Water measured the pressure and flow rate at the meter just outside our boundary as 4.2 bar and 40 l/min - this was after new mains was installed in our street and new bigger bore blue pipe from the mains to the meter. At the same time as they were digging it all up I had the blue pipe extended onto my land and joined to the old lead pipe leading into our house ready for the refurb works. In this form the pressure was measured as 4.0 bar and flow rate still 40 l/min at an inside tap fed directly off the incoming mains despite the lead and 15mm pipework restriction which surprised me - they provided certificate stating this and did have quite a fancy flow rate measuring device rather than a glorified cup. I still have this pressure/flow rate at my outside tap - hope that makes sense?

 

[doitall]

What they have or not in europe is irrelevant to the regulations in this country, end off.

And whilst I'm in a mood, the old boiler cannot and did not deliver anywhere near 40Ltrs/m of hot water, even at 20 bar.

And now I'm going to take it out on a snooker table so good night.

 

[heatingman]

From what you have said,
you had an old high flow w/b storage combi on lead and 15mm and now have a 22/25 main and megaflow. There is no way on this planet that the storage combi could out perform the megaflow. You have some sort of restiction in your pipework. Do you have a water softner?
You might have got a higher pressure from combi (don't think you'd notice difference between 3 & 4 bar when showering) but the flow rate is a lot lower.
The problem is not the megaflow or controls, its the supply in or pipework out.