Megaflo low pressure

ptallett

ptallett

ptallett

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26 Oct 2014
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14
My plumber has installed a Megaflo HP system and we have two digital showers. However we dont seem to have enough flow rate to run both showers at once. The valves for the showers are in the loft and one of them has an app that shows the water pressure at the valve - 2bar with everything turned off. This drops to 0.7bar when both showers are running (dribbling).

Is an accumulator tank the solution to my issue? My Megaflo is 280L so we have enough hot water for 4 people to shower, does the accumulator need to be 280L also?

My plumber says a vertical accumulator would be better than horizontal as it would have a greater head of water, but I thought accumulators worked off mains pressure, not head of water. I'd rather have a horizontal so I can tuck it away in the loft.

Thanks in advance.
Paul
 
In short, yes. An accumulator just stores water at mains pressure until needed. It releases it with vastly superior flow to the mains so it can maintain a higher pressure until all the hot water is gone, so, yes, you ideally need one large enough for all the water you need to shift.
I don't understand his comment about the vertical accumulator either. As you say, they are pressure devices so head has nothing to do with it. Positioning can be important though, which is perhaps what he is babbling about.
 
Okay roll forward a month, we bought two 120 litre Grundfos tanks as anything larger wouldn't fit through the loft hatch. These have now been fitted and seem to subjectively make a difference to the pressure coming out of the taps and showers but basically have not fixed my issue. I can monitor the pressure at the shower valve, and if I leave everything overnight with nothing turned on, pressure is 2.8 bar. The instant I turn on even one shower, pressure drops to 0.7 bar. If I turn on two showers one of them just trickles. Another grand down the drain. Any ideas?
 
He has not been back yet, he is on another job. Its not super rush for me as its only an issue when we have visitors which isn't happening during lockdown.

I don't think he is very experienced with accumulator tanks although he has fitted them before.

By the way since this is really a computing site, here's my rig :)

MSI Vortex i7-6700K @4.0GHz, GTX 1070, 32GB RAM, 43" Dell P4317Q, 2x Dell 30" 2560x1600, 2TB M.2 SSD
 
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To be fair no one here will be able to give you any sort of answer. There are too many variables that have an affect on water pressure and flow. Supply size, position, standing pressure, working pressure, at different points, time of day, pipe diameter and distance, height above ground, type of outlets, condition age of components on pipework, manufacturers own specific requirements (your showers), quality of installation. etc.

All this is gained from on site inspection and testing, by someone how knows what they are doing.
 
whats your connection like coming into the property

have u had a look at the main stop **** outside
funnily enough mine was leaking once it got replaced it really helped.
 
Is your plumber G3 certified? Did he measure the flow rate and working pressure before recommending the Megaflo? You should have 20 l/min at 1.5 bar working pressure as an absolute minimum - and more if you plan on running multiple showers.

What is your static pressure? And what is the pre-charge on your grundfos tanks? An accumulator tank will only hold ~50% of it's capacity, the rest will be full of air. Without pumps, it relies on your incoming supply pressure to build up the charge in the tank, which it then releases when required (ie. showers running).
 
>Is your plumber G3 certified?
No he is not. I was not aware of this certification at the start. To be fair he has done a fab job on the bathrooms themselves.

>Did he measure the flow rate and working pressure before recommending the Megaflo?
No he did not. I was very annoyed when I realised this, but then decided we are where we are and we just need to fix it.

>You should have 20 l/min at 1.5 bar working pressure as an absolute minimum - and more if you plan on running multiple showers.
I isolated the accumulator tanks, ran the cold for a while then let it settle, then ran the kitchen cold tap for 30 seconds - 5.5 litres (so 11L/min). My shower valve is in the loft and is showing 2.4 bar with nothing running. Neither the flow rate or the pressure change when I engage the accumulator tanks and repeat the exercise. I am unsure why I need the flow rate you are suggesting if I have accumulator tanks - I thought that was their purpose? Note the pressure drops to 0.7 the INSTANT I turn on the shower.

>What is your static pressure?
I think that's the 2.4 bar I already mentioned.

>And what is the pre-charge on your grundfos tanks?
1.5 bar

>An accumulator tank will only hold ~50% of it's capacity, the rest will be full of air. Without pumps, it relies on your incoming supply pressure to build up the charge in the tank, which it then releases when required (ie. showers running).
Yes I thought that was how they worked, but I am seeing a pressure drop as soon as I turn on the shower as if the tanks were not doing their job.
 
Some background info.

Our two showers are a Mira Mode dual and a SmarTap triple outlet (although we get the issues with just the rain shower switched on both). We have a MegaFlo tank. The house was built in 1992 and I think we have a water meter. We have a Kinetico Premier Compact Water Softener.

We had our garage converted into a kitchen, so the mains water comes into the front of the house, goes to the back of the house where the kitchen used to be, then comes back to the front of the house under the sink. Then it goes to the water softener and it may even go back to the old kitchen but I don't think so. Then it goes to the first floor airing cupboard, and up into the loft where the valves for the showers are.

I can see we would have a mains flow rate issue, but I would have thought we could even turn the mains off and have a shower from the accumulator tanks or am I misunderstanding (I'm no plumber)?
 
Correct - the context of asking the mains flow was whether an unvented was suited. If it is too low, then an accumulator will supplement the mains flow. The pressure, however, needs to be sufficient to charge the accumulator tank (which yours is - albeit on the low side).

At 2.4 bar mains and 1.5 pre-charge, you will get only 26% capacity. I.e. On a 120L tank, you will get 31 litres of water. Ideally, an accumulator pre-charge should be 1.5 bar below mains. Initially, accumulator will discharge will be greater and then it will drop off until the discharge pressure matches the mains dynamic pressure. Once the accumulator has discharged fully, you'll have just mains flow rate again.

If you are getting such a huge pressure loss even with the accumulator, then it points to a piping issue between the accumulator and the shower. Do you know what size pipes were used and whether there are any obvious restrictions? Is the water softener installed before or after the accumulator (to rule out pressure loss across it). Do you have a bath tap you could try (to rule out the pressure loss across the shower valve)?
 
Thanks. The softener is under the sink so right at the start of the system. I have two 130L tanks (thought they were 120L).

The pipes to the accumulator and all round the megaflo are 22mm copper also up to the tanks in the loft, but the shower piping is in the loft so its lagged but the bits I can see look to be ~16mm plastic. We don't have a bath any more, but opening the washbasin tap it gushes out and the pressure at the shower drops from 2.4 to 2.0.

I think it goes mains->long run->softener->airing cupboard->T junction, one to accumulators, one to megaflo etc. then on to the showers.

Yes, thinking logically, it does point to a restriction between the accumulator/megaflo and the showers - that makes a lot of sense. We've presumably got 2.4 bar'ish pre megaflo, but restricted flow from there to the showers.
 
Is the accumulator BEFORE the cold feed to the megaflo? I.e. both your HW and balanced cold feed (after the combination valve) are being fed from the accumulator?
 
Yes before the megaflo. Plumber just pointed out we have an outside tap plumbed straight into the mains in the old kitchen, I'm getting 20L/min there, can't measure pressure yet.

All the pipes upstream of the airing cupboard are 15mm including the main cold feed that goes to the accumulators.
 
i had this issue - turned out one of the pipes was blocked with a bit of plastic - think it was the pressure relief valve/recharge - hooked out the bit of plastic and all sorted - long shot but apparently its very common. In fact, i called my wifes uncle who is a plumber and without even coming to see it, told me that this would be the issue and it was lol.
 
fastwunz said:
i had this issue - turned out one of the pipes was blocked with a bit of plastic
Click to expand...


Yeah, that's what I'm thinking as well (assuming pipe is not undersized) - could be a partial blockage in the shower valve (the nrv's sometimes get debris stuck in them).

fezster said:
If you are getting such a huge pressure loss even with the accumulator, then it points to a piping issue between the accumulator and the shower. Do you know what size pipes were used and whether there are any obvious restrictions? Is the water softener installed before or after the accumulator (to rule out pressure loss across it). Do you have a bath tap you could try (to rule out the pressure loss across the shower valve)?
Click to expand...

ptallett said:
We don't have a bath any more, but opening the washbasin tap it gushes out and the pressure at the shower drops from 2.4 to 2.0.
Click to expand...
 
But the shower runs fine on its own, I can even have two outlets at once running. Its only when the other shower in the main bathroom is running as well that I have an issue. I'm wondering about a balancing issue - maybe the feed goes to the main bathroom first, then on to the ensuite. So turning on the main bathroom starves the ensuite.
 
It's about the pressure loss with multiple outlets running concurrently. In theory, the accumulator should boost it sufficiently enough to allow both to run - eg. with a 22mm pipe diameter, you can expect upwards of 80 litres/min. However, the longer and narrower the pipe gets, the less the flow will be (as there'll be a greater pressure drop). A partial blockage will drop it even further.
 
Some interesting stats. Bought myself a £20 pressure tester. I have 3.7 bar (20L/min) coming into the house, 3.5 bar at the kitchen sink, but only 2 bar (approx) at the downstairs cloakroom. Pretty sure the cloakroom is fed from the upstairs airing cupboard. Also 2 bar at the washbasins upstairs and showers so that probably means I'm feeding the accumulators with close to 2 bar which would explain their ineffectiveness as its not a lot more than the 1.5 pre-charge. I figure 1 bar is >30 feet of water, so I shouldn't lose 1.5 bar between downstairs and upstairs?

Again, why am I doing this? My plumber should have checked pressures as accumulators seem unsuitable?
 
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