Megaflow supply pressure

[Handyman]

I'm still planning to get a Megaflow system installed (eventually), but I read somewhere that you had to make sure that the incoming water main was of sufficient pressure and flow in order for it to work properly (i.e. provide adequate flow at the taps, etc.) The article suggested that 15mm mains supply was not sufficient unless it was a very short run from the road, and that 22mm should be used. The article gave the example of flushing the WC which reduced the water from the taps to a dribble.

Well, I've got a 15mm copper main supply and it's about 3m from the road (where it changes to water company plastic, I've no idea, because we don't have a stop cock in the road. We have a shared supply with our neighbour, with a joint stop cock about 200m away). There seems to be pretty good flow (even with the WC filling up), but how can I assess whether my mains supply is adequate for a Megaflow system to work at its best?

P.S. What's a tundish?

 

[2scoops0406]

It's more the flow rate rather than the pressure, you can get a hundred psi from a hypodermic needle, but you still won't get very wet. When I had my Megaflow in my old 2 bed cottage, it was fed by a 15mm main, it was inadequate. Mind you, note I'm no plumber so it just conceivably possible I'm talking out of my proverbial.

 

[corgiman]

Heatrae Sadia Stipulate a 22mm minimum feed to a megaflow, so you cant put it on to a 15mm, not if you want them to honour any guarantee that is

 

[Handyman]

I appreciate what you say, Corgiman, but to achieve the 22mm objective, it looks like I'm going to have to dig up the main until I find where it connects to the supply company's plastic pipe, and then get it replaced with 22mm............ Mind you, I could then get my own stop cock put in which would be useful. But what a lot of extra hassle and expense, though

 

[corgiman]

pretty much, if thats what you have to do to conform to what the manufacturers say then thats what you'll have to do

oh dont forget that the local building authority have to be informed of its installation 10 days prior to work being undertaken, and also dont forget to include proof of your unvented competency certificate with the notification!

 

[corgiman]

If you dont know what a tundish is I really really hope you are not thinking of installing this cylinder yourself

 

[Handyman]

Err... no, Corgiman. One or other of two local plumbers will do it, but I like to know what's going on. If it requires a 22mm supply, then I can get this sorted in my own time, before the plumber tells me I need to do it before he can commission the system.

So, what's a tundish, then??

 

[corgiman]

Oh Ok

a tundish is a warning device that gets installed on the outlet to the temperatur and pressure relief valves and lets you know when they are letting water by because you can see it.

word of advise make sure that these plumbers do have the relevent competency qualification to install unvented cylinders, they probably have but better safe than sorry

 

[Handyman]

Define "competency qualification".....

 

[corgiman]

for example G3 registration as laid down by CITB (construction industry training board)

as water regs state that only proven competent persons shall install unvented cylinders with a capacity of 15 litres or greater

 

[Handyman]

Duly noted. Thanks for your help and advice, Corgiman.

 

[ChrisR]

I don't believe they can insist you have a particular size supply pipe - that's ridiculous! I put an unvented system in on a long 15mm supply which was at 8 bar. Perfectly obviously, there were no problems at all. Two separate taps ave 22l/min at the same time, iirc.

The Megaflo reduces the input pressure to 3.5 bar (or is it 3.0). The flow used to be restricted massively by their valvery, which was tiny diameter inadequate stuff, and which I understand has been improved.

You do, as you have been advised, need to measure what pressure and what flow you have. Call your water supplier to get the predicted pressure for your postcode, and you can measure it with a £12 gauge.
To check the flow turn all/any mains taps on together - kitchen sink may be the only one, but usually an outside tap too. Add the flows (use a 9 litre bucket, say) in a minute to get your flow rate in litres/minute, with the supply pipe you have.

If you have 1 bar mains, you'd be utterly wasting your money on a Megaflo, however big the incoming pipe.

 

[bab]

Not sure what pressure mega flows reduce to but if u are lower than 2,5 bar OSO reduce the inlet pressure on there cylinders to 2.1bar once went to a noisy prv on a megaflow ,banging & whisling. turned out to be the inlet pressure was only 1.5 bar & when the water was heated & the pressure lifed in the cylinder it was greater than what the prv was set to but the inlet was less than that. Only cure was to reduce inlet prv down to 1.5bar same as incoming pressure.

 

[ChrisR]

the pressure lifed in the cylinder it was greater than what the prv was set to but the inlet was less than that.

Err, um,
eh??
On half the unventeds I look at the mains is lower pressure than the Pressure Reducing Valve is set to - not that a M one is adjustable as far as I know (?)
Sure the pressure in the cylinder goes up a bit on heating - until a tap is opened. DOn't see why that should cause a problem.

 

[Handyman]

Hello ChrisR and Corgiman.
Right: I've done what you said. I bought a mains pressure test valve. Pressure is 8.5 bar. Then I opened (full on) all the direct-fed taps (of which we have three) and timed flow for one minute, collecting the water in buckets. Flow appears to be 28litres/min - that's from all 3 taps collectively.

So, are these figures OK for a Megaflow to work as it should?

Water Company have been and are now deliberating about whether to give me a stopcock of my own. If they don't I'm gonna have to stick with my existing 15mm copper main, rather than increase to 22mm.