how to calculate gallons per minute through a1" pipe 50' long at 20 psi?

Answer 1

Yes, you can do it, but it will require iterations.

1) Convert all units to standard engineering units (feet, pounds, seconds).

2) Set up the mechanical energy equation:
(p2 - p1)/gamma = z2 - z1 + (f*L*v^2)/(2*D*g)
where p2 -p1 is the pressure across the pipe (20 psi, but convert to lb/ft^2), z2 - z1 is the rise in the pipe (if any), gamma is the specific weight of water (62.4 lb/ft^3), L is the length of the pipe (50 ft), D is the I.D. of the pipe (ft), and g is the acceleration of gravity.

3) Now you have a problem: v is the velocity of the water, and f is the friction factor, which depends on v. So, you guess a value for v, and calculate f from it. You look up f on a chart (it's called a "Moody chart"). But you'll need the Reynolds number and relative roughness of the pipe surface to do that. Then you try another v, find f, etc. Or, you can try this:

http://www.fluidmech.net/jscalc/vmd03.htm

4) Just keep plugging in different velocities until the head loss (right side of the equation) equals the left side. Then convert to volumetric flow rate.

Hey, I get 14.2 ft/s, 0.0774 ft^3/s = 34.7 gpm

Answer 2

Not enough info dude. BUT... Interestingly if the pipe goes vertically (straight up) off of the 20 PSI pump it wont pump anything and your flow will be ZERO.
Example; 1 PSI of water = a column of water 27.7" high.
50 ft of pipe = 600"
600" divided by 27.7" = 21.66 pounds.
SOoo. The pump would have to produce over 21.6 pounds to pump anything. It would just cavitate until it burned up...
In this case the answer would be ZERO,

Answer 3

Unsolvable with the junk information you've given.

20 psi where? 20 psi in the pipe? 20 psi on one side relative to the other? 20 psi in the atmosphere? 20 psi plus atmosphere?

"At 20 psi" tells us nothing, it needs to be relative to something.

Answer 4

I am looking for the GPM of a 8 inch pipe at 40 psi and I was hoping to see your calculations for your answer and convert this to my problem. I am trying to remodel my house and the Fire Marshall wants me to put a fire sprinkler system in my house. It will be about 20 thousand dollars. Any help would be appreciated. steve

Answer 5

Q = flow per time = area multiplied by velociety

this is a good starting point

you can also subsitutite the energy equation for Q and maybe get what your looking for

Answer 6

What is the fluid, any bends or change in elevation?

Answer 7

Take a look at this page

http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm#calc