Doctor Drivel wrote:
"Mark BR" wrote in message
...
Can a plumber give me a simple answer to what I think is a simple
question?

I'm working with a building in Thailand to improve the water supply.
Currently we have a pump and pressure tank that can just get up to
2.5Kg/cm (2.5 bar). This pressure is just enough. Problem is when it
reaches pressure it switches off and only comes back at 1.7 bar, not
enough for most rooms. So we get a varying water supply from a
trickle to a surge. If we leave the pump on continuously we use far
too much electricity.

We have a lovely electric pump, 8 amp so plenty of power, and a
header tank 4 metres above the pump.

Can I just change the water pump part - is that the impeller?

See the makers, but I doubt it. Get a pump with a lower switching
differential. Also put a non return valve just before the pump.
Between the valve and pump install a potable pressure vessel. This
will help prevent pump cavitation and a more even water distribution.
Some pumps come with the vessel as a set. How is hot water supplied?
Via a cylinder? Vented? Unvented?

If you get anew pump use the old as a backup.

If I change it for a pump that can get up to 3.5 bar is that the
same as a pump that can give a 35m lift?

Yep. 1 bar = 10 metres

Thanks, a lower switching differential would work but most seem to be about
0.7 bar between on and off. As the maximum the pump can achieve is 2.5 bar,
and that is the minimum acceptable then any differential is too much - so we
do need to be able to pump more.

We do have a pressure vessel and a non-return valve. Improving these did
improve the system but not by much.

The cost of the pump is not much of a problem, locally we can get pumps
(motor and water pump part) with 30m lifts for around £50. But we can't
really afford to get one and find out it is the wrong one, so I'm trying to
get information.

Thanks for your comments

--
Mark BR