Pump-assisted pressure for house hot water

Advice, please, on providing pump-assisted pressure to house hot water: I want to pressurise the gravity-fed hot water supply in my house in order to get strong showers (2 existing showers on 1st floor) and new shower (about to be installed) on the ground floor. The ground floor water supplies are mains cold and gravity-fed hot.
The 1st floor showers are Trevi-boost which relies on a venturi-effect mains water jet to add pressure to the mixed hot/cold shower. These do not work very well. The hot water cylinder (vented) has 3 hot water outlets: 2 for the 1st floor showers and the 3rd for the general hot water in the house. I plan to close off the vent so that the hot water cylinder can be pressurised by a pump placed in the water inlet feed to the cylinder. Any excess pressure caused by hot water expansion or other reasons will be relieved simply via the inlet pipe back up the cold water storage tank in the loft. Will this approach work?
--
rgordon


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rgordon wrote:

Bad idea, I don't think you're allowed to "un-vent" a normal vented tank. The normal location of the pump is on the HW outlet from the tank. I would just block of two of the three outlets and use whichever one is least likely to entrain any air drawn down the expansion pipe.
A more expensive but better option might be a mains pressure tank if your supply pressure and flow are good.
Tim
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Tim Downie wrote:

+1
this rapidly becomes cost affective if you are having to install more than one pump.

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On Wed, 04 Jul 2012 13:01:22 +0100 (BST), "Dave Liquorice"

Well, they will withstand 1, 2 or 3 bar, and that depends on the grade of manufacture.
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If you've seen video of what happens to an unvented cylinder overheating if the pressure relief valve doesn't work, it's not _that_ odd that people are a bit cautious when you mention pressurizing cylinders that aren't designed for it:
http://www.youtube.com/watch?v=ekEHfihiNz4

http://www.youtube.com/watch?v=Xi_p23dce8U

(Yes, I do know what you're talking about isn't the same thing.)
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On 03/07/2012 13:49, rgordon wrote:

Only do that if you want a very expensive explosion! Normal hot water cylinders will *not* stand pressurising beyond that provided by gravity from a cold header. You'll push the bottom out and have a *very* wet mess!
--
Cheers,
Roger
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On 03/07/2012 13:49, rgordon wrote:

I have mains pressure hot water .. but this is via Thermal store, so much in fact I have to limit flow rate.
Not sure how practical it is on gravity system
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