I know shower pump questions come along all of the time, but I can't seem to
get my head round this scenario.

I have a standard (is there such a thing?) hot water cylinder in my airing
cupboard. This has its cold feed from the storage tank in the loft, probably
some 2m+ above the inlet to the cylinder. The cylinder is a new one which
has a flat top, not domed, and has a jacket (not that foam dipped look).

If you have a pump, mounted on the floor of the airing cupboard, and this is
sucking from an Essex flange, if the cold water supply rate to the cylinder
is less than the hot water pump rate, won't this result in problems? Surely
the level of water in the cylinder will lower and air will be drawn in
through the vent, and that the domestic hw will also be cut off when the
vent empties?!

I can't see how this always isn't a problem, or does the height of the
coldstorage 'always' provide a higher flow rate than a 1.4-1.8 bar pump?

I'm sorry for being so thick!

I'm sorry for being so thick!


I wouldn't worry about that - there are loads of thick propel in this NG!

I can't say why but it doesn't cause problems because that's exactly how my
shower pump is plumbed in. I guess the head of water does compensate enough.

In article , Graeme
writes
I know shower pump questions come along all of the time, but I can't seem to
get my head round this scenario.

I have a standard (is there such a thing?) hot water cylinder in my airing
cupboard. This has its cold feed from the storage tank in the loft, probably
some 2m+ above the inlet to the cylinder. The cylinder is a new one which
has a flat top, not domed, and has a jacket (not that foam dipped look).

If you have a pump, mounted on the floor of the airing cupboard, and this is
sucking from an Essex flange, if the cold water supply rate to the cylinder
is less than the hot water pump rate, won't this result in problems? Surely
the level of water in the cylinder will lower and air will be drawn in
through the vent, and that the domestic hw will also be cut off when the
vent empties?!

I can't see how this always isn't a problem, or does the height of the
coldstorage 'always' provide a higher flow rate than a 1.4-1.8 bar pump?

Yes, I think it would, unless the storage tank empties because the fill
rate is lower than the pumping rate (has happened in our house).

You need the pump to force the water through the little shower jet
holes. But there is more flow rate through the 22mm cylinder feed pipe
than through the shower, even at the lower pressure of the cylinder.
--
Tim Mitchell

all my nonsense snipped !

"Tim Mitchell" wrote in message
...
In article , Graeme
But there is more flow rate through the 22mm cylinder feed pipe
than through the shower, even at the lower pressure of the cylinder.

Then this answers my question. Thanks.
So what is the flow rate through a 22mm pipe with a standard cold storage
tank?

Still sort of OT, where would you tap my cylinder to put in a flange? Top
(flat) or side?

Then this answers my question. Thanks.
So what is the flow rate through a 22mm pipe with a standard cold storage
tank?

That would depend on the head of water and that varies with the level in the
tank. Another factor maybe the rate of use of water from the hot tank. A lot
of factors indeed.

Graeme wrote in message ...
Still sort of OT, where would you tap my cylinder to put in a flange? Top
(flat) or side?


If it's an Essex flange, a few inches down the side 6"? If it's a Surrey
flange, at the top. Yes it's possible to exceed the flow rate through the HW
tank when pumping. This can be alleviated by using separate 28mm feeds for
hot and cold supplies from the roof tank through to the pump where possible.
Using both Essex and Surrey flanges on the hot tank also helps at high flow
rates or the pump may cavitate. A big loft tank 100+ gallons helps. (Big
showers use over 3 gallons/minute) Ensure that all stop valves are fully
openable! Mount pump as low as possible to get the best gravity fed flow
rate into the pump.

Regards
Capitol

"Graeme" wrote:

Hello Graeme

G| If you have a pump, mounted on the floor of the airing
G| cupboard, and this is sucking from an Essex flange, if the

Mine's the same, except using a Surrey flange. No big difference
though.

G| cold water supply rate to the cylinder is less than the hot
G| water pump rate, won't this result in problems? Surely the
G| level of water in the cylinder will lower and air will be
G| drawn in through the vent, and that the domestic hw will
G| also be cut off when the vent empties?!
G| I can't see how this always isn't a problem, or does the
G| height of the coldstorage 'always' provide a higher flow
G| rate than a 1.4-1.8 bar pump?

I wouldn't worry.

The water level in the vent and the main supply tank will be the same,
so to empty the vent enough to suck air in it would need to drain the
tank pretty much. I suppose it's theoretically possible if the route
to the tank is convoluted or the valve there is half closed, but in
practice it doesn't seem to be an issue.

I'm not sure how much pressure rating affects things. I've got a 3-bar
pump, but I don't think that changes the flow rate much. That's more
down to speed of impellor rather than size of motor, I'd guess?

--
Simon Avery, Dartmoor, UK
uk.d-i-y FAQ: http://www.diyfaq.org.uk/