What is the height above the water main, above which the water will not flow?
The pressure in a city water main is 50 psi. The pressure loss through piping, fittings, and the water meter can be ignored for this exercise. What is the height above the water main, above which the water will not flow? Given: h=2.3 psi
Answer: 115’
h=2.3 P
h=2.3 * 50psi
h=115’
So if you extend a pipe to 116 feet higher than the water main, there will be no water pressure at that altitude in that pipe. You could look down inside that 116foothigh pipe and see the top of the water column one foot down into the pipe, but the pipe could be uncapped and water wouldn’t flow out of it.

1/2.33 = 0.433. . . It's like converting km to miles and back. . . you use one number (1.6) to convert miles into km and the inverse of that number (1/1.6 = 0.62) to convert km back to miles. Or pick your favorite foreign currency: you use one number to convert to dollars from the foreign currency and the inverse of that number to convert the other way.
So for plumbing, we use one number for multiplying times the height to get pressure. . . p=.433 x height
and the inverse for multiplying times pressure to get height. . . height = 2.3 x p
It's a bit more intuitive to convert height to pressure. . . if you hold water in a water tower 100 feet above a fixture, we can understand how the pressure may increase if we increase the height of the water tower to 200 feet above a fixture. . . it's a bit unintuitive sometimes to think of converting pressure to height, but if water enters a building at some pressure, let's say 60psi, and you run that water up an uncapped pipe, moving up through the floor plates, at some height high enough, the pressure will be gone such that, if you stick your finger inside the open end of the uncapped pipe and pull it out, your finger will be dry. Not enough pressure to push the water past a point a few floors down. How high can 60psi move up before the pipe gets dry?
height = 2.3 x p
height = 2.3 x 60'
height = 138'
So if the floor you're standing on is 175' high, and you put your finger inside the open pipe, it will be dry. But if you drilled a hole in the same pipe at 100' high, you'd watch water leak through the hole.

how would you calculate the pressure at a certain height along the pipe?
if the water pressure entering the building is 60psi & it enters the building @ + 0'0" what would the pressure be on the second floor with finish floor @ +10'0" if the pipe entered the sink @ 2'6" high
p=.433 x 12'6"
p=5.41
p= 60  5.41 = 54.59??
sorry i think i got away from what you were originally asking
Please sign in to leave a comment.
Comments
6 comments