can i pump mains pressure water?

[Chris]

To explain - I've just installed a Pandora heat bank. This replaced my previous system which had a cold water tank and how water cylinder, with a big American pump to give me a really excellent shower.

I have to say that I'm a little disappointed with the pressure from the cold mains. I will be getting my plumber to have a look at the pipe runs etc, to ensure that I am getting the most from my current system. However I suspect that i've just been spoiled by the luxure of having a pump.

So my question is, what would happen if I put the pump back in circuit? I'm confident that the Pandora could cope with the increased heat demand. But would I be able to significantly increase the water pressure? Would this have any knock-on effect for my neighbours? And what would Thames Water say if they found out (and would they ever find out?)

Many thanks,

Chris

[Ian Stirling]

The basic problem is that if you reduce the pressure in the pipe to less than atmospheric (as is quite possible to do) that you suck surrounding water in through any leaks.

[Andy Hall]

Oh dear.

Yes.

Unfortunately it's not allowed by the water byelaws.

THe only things that you can do are to increase the pipe sizes (perhaps back to the street), check that the stop c*ck is a full bore type (change if not); and after that consider a water accumulator. These are a pressure vessel which stores water and is filled from the main. You can use the contents more quickly than it is filled for a period of time - e.g. a shower.

[Peter Stockdale]

I would think that the only acceptable way to pump mains sourced water is via a storage tank - whatever the end purpose.

Pete

[Christian McArdle]

Yes, a mains pressure hot water system is totally dependent on the mains to provide acceptable levels of pressure and flow. If these are not present, then they won't work well.

To fix it, there are two general approaches.

1. Reinstall the cold water cistern and pump. The Pandora will just as happy heating gravity pumped water as mains.
2. Fix the mains supply. You can only do this if the water pressure is good enough in the street. You need to find and fix the bottleneck between the street and your hot tap. This could be a tiny 15mm water supply from the street, or scaled up pipework, or simply a half closed stopcock. A bit of investigation is called for.

What is not an option is pumping the mains. This will lead to negative pressure on the supply pipe which will cause the myriad of leaks in Thames Water's pipework to start sucking in manky ground water rather than squirting fresh water out.

Christian.

[Pete C]

Would be worth measuring the static mains pressure at peak times, then the pressure at the stopcock when the shower is on. This would give the maximum possible shower pressure, and how much flow restriction there is before the stop c*ck or by the stop c*ck itself.

If you did use a pump on the mains then it would be well worth having a non return valve on the pump inlet to air. This would stop the mains pressure going negative by allowing air to bleed in. Definately not an approved way of doing things though.

I'd expect there are dedicated mains booster pumps available that have a low pressure cutout.

cheers, Pete.

[IMM]

Only in exceptional circumstances will mains pumps be allowed. It will probably be cheaper to replace the whole mains pipe back to the street and then no pumps to make and noise, take up space and go wrong.