pneumatic and gravity mixing

[vij36]

Dear All,

I am having a very basic understanding of mechanical. So please bear me if any thing does not make sense.

I have a task of installing a pneumatic pump at the 7th floor height of a building.
The location experiences power cuts some times.

So we want to mix both pneumatic and gravity.
In case of power failure how to ensure proper pressure at the 7th, 6th and 5th floor ?

Also will there be any chances of hot water(being more pressurized) mix with cold water at the diverter ?

Your help is appreciated.

Thanks,