If you have a multi story building and with 40 psi water pressure coming in at what height do you put a booster pump?

This depends on what your target pressure is.

If the height of the pipe is H in feet, the pressure at the bottom of the pipe from the column of water is 0.036127292 * H * 12 where 0.036127292 is the density of water in lbs/in^3. Thus, if your initial water pressure is I, the pressure at H feet will be I - 0.036127292 * H * 12

So you will have

Height | Pressure

+---------

0 ft | 40 psi

10 ft | 35 psi

20 ft | 31 psi

30 ft | 27 psi

40 ft | 23 psi

50 ft | 18 psi

60 ft | 14 psi

70 ft | 10 psi

80 ft | 5 psi

90 ft | 1 psi

100 ft | 0 psi

One will be required above 90 ft. You'll probably want one above 40 ft.

Derivations: eq means equals. This wiki eats equals signs.

D eq diameter of the pipe in inches, H eqheight in feet

D / 2 eq R

Area (A)(in^2) eq pi * R ^ 2

Volume (V)(in^3) eq A * H * 12 eq pi * R ^ 2 * H * 12

Water weight (W)(lbs) eq V * 0.036127292 eq pi * R ^ 2 * H * 12 * 0.036127292

Pressure (P)(psi) eq W / A eq V * 0.036127292 eq pi * R ^ 2 * H * 12 * 0.036127292 / pi * R ^ 2 eq H * 12 * 0.036127292