Simple Formula for pressure in pipe

[eegeek]

I am looking for a simple formula to compute pressure drop in a straight new pipe(basically no friction). Its just a simple 2' straight pipe with water flowing in it. How do you figure pressure drop? Is there a simple formula for pressure drop in a pipe?


Thank you for your time.

 

[JStephen]

Check Moody chart or equivalent equations in a fluids book or engineering handbook.

Unless the pipe is awfully small or the flow rate is awfully high, the pressure drop in 2' will be negligible.

 

[cvg]

use Hazen Williams Hydraulic Tables / formula
V = 1.318C * r^.63 * s^.54

V = avg velocity
C = discharge coefficient
r = hydraulic radius
s = h/l = energy loss per foot of pipe

values for C can be found in many textbooks and vary depending upon size, type and condition of pipe

you may also want to try the Handbook of Hydraulics by Brater and King

 

[CountOlaf]

Before you get too caught up in the equations, there are plenty of tabulated books for easy reference. Just tell us the pipe material (steel, copper, plastic, etc.), the size of the pipe (nominal diameter or actual), and the flow rate (gpm) or velocity of the water.

 

[eegeek]

Thank you for all the input ... the pipe is copper the id is .5 its actually two 24" lengths joined by two 90s and a 4" section of pipe to make a long U the flow is 2.5 gpm.


Once again thank you for all the help.

 

[DRWeig]

eegeek,

I think you'll have not much -- something between 0.5 PSI and 1 PSI drop. If you desire accuracy, plug your data into the calculator on this link:

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

If you consider your two elbows to be equal to about 4 feet each of equivalent straight pipe length, you'll be pretty close.

Enjoy!

Old Dave

 

[CountOlaf]

I agree with Old Dave's approximation. I get about 0.7 psi or 1.6 ft H20 drop. I was assuming about 3.1 ft of equivalent length for each elbow which brings your total "hydraulic" lenght up to ~8.53'.

 

[cvg]

eegeek: this is the pressure drop for headloss due to the flow velocity. you may also need to add (or subtract) due to the change in elevation from one end of the pipe to the other.

 

[CountOlaf]

Oops. Forgot to add in the last 2'. I should have said:
0.86 psi or ~2 ft H2O drop (based on an hydraulic length of 10.53' and a pressure drop of 18.8'/100').