Hi,

I am looking to install a shower with a booster pump, but am wondering about
the best way to do it.

The set up is as follows: I have a system boiler, so all the cold water in
the house is mains pressure, but the hot water is held in a cylinder in my
airing cupboard and is supplied from a header tank directly about it in the
attic.

I wish to fit a shower in my bathroom, which contains the airing cupboard.
The shower is a exposed valve thermostatic and needs higher hot water
pressure.

The obvious solution is to fit a double-ended pump, supplied with hot water
from the cylinder and cold water from the header tank.

However, I am considering an alternative, which is to use a single-ended
pump to take hot water from the cylinder to the shower valve and take the
cold water from the mains to the shower valve, but put a pressure equalising
valve before the shower valve.

The rationale for doing the above is that it should mean that the header
tank only empties half as quickly, because it is only supplying the hot
water, and so allowing for a longer shower.

I asked the question elsewhere and got the following reply:

"In theory this is possible but you will probably find that joining the
cold after the pump means that the increased rate of the hot may "suck" cold
out of the tank faster than it wants to go and cause all sorts of air
problems."

I'm not sure why this might happen, but I don't understand how pressure
equalising valves work.

Thanks for any advice.

Carl