New 32mm supply with Megaflo but poor pressure & flow

[jjrideon]

Hi,

I'm just finishing refurbishing my 1st & 2nd floor maisonette in London.

A new 32mm water supply was fitted by Thames Water (previously 3 flats shared the one supply.) The plumber put the stop cock on this in the communal ground floor level cupboard where it previously was, reduced to 22mm copper and ran it upto the 2nd floor where the Megaflo / Worcester system boiler are. From here it feeds 2 bathrooms, a WC & Kitchen.

In the 3rd floor bathroom tap water pressure is only just over 1 bar, and the flow rate is 10 litres per minute. It makes the large Hansgrohe shower head a bit of a joke. It's pretty much the same on the 1st floor bathroom too. Kitchen tap on the 1st floor seems much better but I need to get this tested.

I've had a couple of new plumbers look at the installation for advice and have been told different things. (Original plumbers don't work for the main contractor anymore and he's dragging his heals getting someone else in to check.)

First guy said the 32mm pipe should have been run up all the way to the top floor and this would have increased the flow rate substantially. Didn't really have any comments on the pressure.

Second guy said this was rubbish as the pipe is reduced when it reached the megaflo anyway, and reducing to 22mm on the ground floor increases the pressure too. He said the only thing to do was fit a header tank on the roof & pump.

The pressure is over 3 bar to the ground floor flat in the building which is on it's own new 32mm supply as well (reduced to 22m at the same point in the communal cupboard. I don't know the flow rate yet.) My Megaflo is around 10m up from ground level so I don't know why I'm losing 2 bar in pressure, and am confused about how to try and get a better flow rate too.

If I'm missing any information needed to help please let me know and any help is greatly appreciated!

Jay

 

[snb]

Would be best to remove and clean the filter on the pressure reducing valve (supplied with megaflow) this could have debris from the changes.

also double check that all valves are fully open including the 1/4 turn isolating valves (if fitted) just before taps.

you could also remove the stariner in the tap head to make sure this is not full of installation debris.

 

[jjrideon]

thanks for the reply
all of these have been done - there was quite a lot of rubbish in the tap head strainer for example. the flow rate was even worse before this was done!

 

[simond]

The static pressure should be around 1bar less on your floor if there is 10m of height difference.

But other factors can come into play here; for instance, if one of the modern WCs are letting by through an internal bowl overflow you will measure a lower static pressure.

Both of your advisors were talking rubbish. The 22mm pipe will not increase or decrease the static pressure, but the smaller the pipe, the lower the flowrate you can expect to achieve.

Bear in mind that the pipework may run upwards after the Megaflo to your bathrooms and therefore the pressure drop needs to take this into account.

There are two solutions; an accumulator (if the pressure is 2bar) a pumped accumulator (if the pressure is lower) or something noisy like a Grundfos Homeboost.

Getting Thames Water to raise your pressure is usually not on the cards.

 

[jjrideon]

thank you simon.

1. there is no space for an accumulator on the ground floor or basement. there is also only around 400mm loft space (it's a stepped flat roof) is something on the roof an option?

2. i'm going to get the pressure and flow rate tested again at each floor. i'm sorry, but can someone explain the difference between static and working pressure and how you test this?

3. what would be an 'acceptable' flow rate considering the entire plumbing/heating in the flat has been re-done and if the mains is re-run in 28 or 35mm?

4. if the mains is re-run - can it be run in polypipe? the mains from the street is 32mm I thought so should it stay in 32mm (or be 28 or 35?)

thanks again,
jay

 

[simond]

There is no 'acceptable' minimum flow rate, other than the point at which your supply is below the statutory minimum, this is around 9 litres per minute.

If you only want showers (one at a time) 12 litres a min is acceptable; but if you want a Megaflo to deliver anywhere near to the minimum level that the manufacturer decrees worthwhile, you are looking in excess of 20 litres per min.

Sometimes people get the idea that magical and mystical things happen by increasing pipework, from reading this forum. Any pipework will restrict flow rate, but upsizing a 22mm pipe to 32mm from downstairs is unlikely to make any measurable improvement in your case, because the supply is poor.

Ironically, if you were blessed with a 40litre per min supply from Thames Water, the larger pipe would deliver benefits.

Regarding the siting of break tanks and pumps, or accumulators, this is usually not your best use of a forum because we can't see your property, there's nothing to beat a site visit.

Maybe the next version of Google maps will sort this out

 

[doitall]

Disagree with you there Simond.

The jjrideon has 3bar+ at street level, and only 1 bar on the 3rd floor a lose of 2bar over 10m.

I don't know if that's static or working pressure but irrespective of that the loss is too great. indicating either a blockage or pipe restriction, and if the later a larger pipe would increase the flow rate considerably.

Assuming a static pressure of 3bar then the op should be looking at 2bar 10m higher.

Proper checks on the pressure need to be made at peak and off-peak times. only then can one give good advice.

 

[simond]

I can see where you are coming from in respect of working pressure (to the OP, this is when water is actually flowing).

In terms of the static pressure, if the pipe was restricted down to 6mm diameter to the upper floor, the static pressure measured would be the same as a 32mm main.

There is an anomaly with the pressure readings versus height given, I suspect this is because the guage is either faulty, or the lower reading is influenced by a small draw off somewhere ie: a bog.