Bottom Fill

Which requires the more force?

The following question frequently presents itself: Which requires the more force, to fill an elevated tank by pumping the water directly into it through the bottom, or to fill it by means of a pipe leading over the top?

 

The answer is that more work or force is required when the water is pumped over the top of the tank. Contrary to the popular notion, the water going into the tank from the bottom does not have to lift the entire weight of the water into the tank; it lifts only a column of water of the same area as the pipe. The level of the height and not the weight of the water governs. If you lift a column of water over the top of the tank it is clear that you must lift it higher than if you force it into the tank from the bottom. The pressure of a column of water in pounds to the square inch is calculated by multiplying the height of the column in feet by .434.

This came from the A Book About a Thousand Things, by George Stimpson, copyrighted in 1946 by Harper and Brothers.

This brings up a good point to remember if you are limited in piping supplies and power to push water. One could have a storage tank fed from the bottom and covered on the top (no trash, debris or kids could fall into the tank) with an outlet for water on the side of the tank near the top or the bottom. A shut off valve could be installed in the inlet tube going into the bottom of the tank to stop the water from back flowing into the pump until next time water is needed to fill the tank. Need to prime your pump? Just open the valve a little.

Offered by Clip.