Twin impellor pump to feed whole house

[AdamW]

I was hoping someone could satisfy my curiosity here.

1) Is it advisable to use a twin-impellor pump in a situation where water will only be flowing through one impellor at times? I was talking to a colleague recently who mentioned that he has bought a continuously-rated 3bar shower pump, with the intention on pumping his whole house water supply with it. There are situations where cold water will be required on it's own (filling toilet, washing machine etc). I know little about pumps, but this just seems like it will be putting strain on the pump. Or is the design of an axial impellor such that the water will just swish around in the pump without putting a strain on anything?

2) Also, I have a quick question about negative head pumps. When running in a negative head situation, do these pumps automatically switch on when you open the shower valve? If so, how does that work? I am guessing the pressure switch measures backflow, instead of forward flow, am I close?

 

[ChrisR]

1) depends on the pump. Ask the manufacturer. A Stu Turner Monsoon will stand it for quite a while.
Best if you don't pump the loos, or the pump will be on and off a lot - or use a timer on the pump to turn it off at night.

2)
N H pumps have a pressure switch not a flow switch, and a small pressure vessel which they keep at say 1.5 bar. So when you open a tap upstairs the pressure's there, and when it dropsto say 1 bar the pump starts.

 

[AdamW]

Cheers Chris, another mystery solved!