On Sat, 10 Apr 2021 13:09:51 +0100, Roger Mills wrote:
On 10/04/2021 08:42, Tim+ wrote:
Roger Mills wrote:
I am planning to re-furbish an en-suite bathroom, and am considering
installing a Stuart-Turner Monsoon twin impellor pump. I currently
have a Mira Vigour wall-mounted power shower with built-in pump but
would like to replace it with something with a bit more €śurge€ť.
The instructions for the Monsoon say €śThe pump must, for optimum
performance, be sited as close as possible to and never more than 4
metres from the HOT WATER cylinder€ť.
In my case this would be very difficult to achieve because the hot and
cold feeds to the en-suite take different paths and only meet when
they get there (see drawing at
https://app.box.com/s/20x0sg5z9rpwsh27mi2wwsth3d7fk5g0). The hot runs
under the landing and bedroom floors, and the cold runs through the
roof-space. If I install the pump in my preferred location inside a
vanity unit in the en-suite, the pipe run from the hot cylinder to the
pump would be about 10 metres. I have spoken to a droid on the S-T
support helpline, who simply reiterated what it says in the
instructions but wasnt able to explain the rationale behind this. I
am struggling to understand which law of Physics would be violated if
the distance between hot cylinder and pump is more than 4 metres. How
does the pump know how far it is from the cylinder? If it's a
cavitation issue, isn't head and pipe size more important than
horizontal distance? What are the likely consequences of installing it
in my preferred location? I accept that I may need an Essex flange (or
similar) in the cylinder to avoid sucking the vent pipe dry.
Am I missing something?
I fannied around for years with pumps, and then upgraded to an unvented
cylinder. Wish Id done that to start with.
Unless you have poor mains pressure in which case your options are
limited,
Id suggest an unvented cylinder (or a thermal store).
In my holiday flat I've got an unvented cylinder allowing mains pressure
hot and cold to be supplied to a bar mixer - but it doesn't have
anything like as much urge as I would like. It's worse than my current
rather feeble "power shower" at my main home.
If you still want to go with a pump could you not put your pump by the
HW tank and run the cold feed to the shower back up to the loft and tie
it in there?
Possibly, but it's a bit messy bringing the cold down and then up again.
No-one has yet explained why my preferred solution wouldn't work.
I think the general theory is that sucking sucks compared to blowing.
The pressure drop on the input is likely to be the main problem, and the
further the pump is away from the tank the greater the pressure drop is
likely to be.
Also if you have a cold and a hot feed going by very different routes then
there might be an imbalance on the input side of the pump. This seems less
likely. However if there is an imbalance then this might cause the mixer
valve problems if the outputs are unbalanced.
A long time ago, but IIRC there was a separate dedicated cold feed from
the loft down to the side of the hot water tank and some kind of flange
near the top of the hot tank. So in theory hot and cold were drawn at the
same spot and at the same pressure.
You could possibly have two single pumps but that sounds complicated to
set up, and assumes the cold feed only feeds the shower.
Although thinking about it you would have to have a dedicated feed to a
pump, otherwise you would be sucking on any cold taps or toilet cisterns
sharing that feed when the pump was on.
Is it practicable to add a large cold feed to the airing cupboard and then
run a new cold feed to the shower alongside the existing hot?
A lot more work but removes a lot of the unknowns.
Are you prepared to do this if you try your approach and this fails?
Memories also, we managed to empty the hot tank quite quickly and had to
have a larger one fitted.
We then (more occasionally) managed to empty the cold tank in the loft if
we had both showers running at the same time. Rare enough not to warrant
fitting a bigger cold tank.
HTH
Dave R
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