I would like to know how to calculate the water pressure
for gravity fed water supply systems. I am doing a 4-H club project on
supplying water to livestock from a water storage tank.
What is the formula for calculating the output pressure of a tank given
the factors of tank size and elevation and the size of the output pipe?
It's really easy. If the vertical distance between the spigot and the
surface of the water is H inches, and you want the pressure in pounds
per square inch, you just calculate the weight in pounds of a column of
water one inch square by H inches high. The size of the output pipe
does matter a little, because causes a pressure drop, but at the water
speeds you're interested in the effect is small unless the pipe is very
narrow or very long. A garden hose, for example, doesn't produce much
of a pressure drop at household water pressures.
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Update: June 2012