# How can i calculate pressure drop in air compressor?

noname91
hi friends,
I am confused with incompressible and compressible flow.Can i use moody diagram for air compressor.How can i calculate pressure drop in pipe.

## Answers and Replies

Staff Emeritus
Homework Helper
As long as the velocity of the air flow < 0.3 Mach, the incompressible flow equations (Darcy-Weisbach) can be used to calculate pressure drop in a piping system. Once speed > 0.3 Mach, then a different analysis using compressible flow is called for.

I don't know what you mean by 'Can I use moody diagram for air compressor?'

Crane Technical Paper 410 covers some simple compressible flows for air and other gases. It's worth laying your hands on a copy.

noname91
I found a formula from atlas copco manual
p1-p2=(450*(q^1,85)*L)/((d^5)*p)
q=air flow (l/s)
d=internal pipe diameter(mm)
l=length of the pipe bar(a)
p=absolute initial pressure

atlas copco products air compressor.Can i use this formula to calculate pressure drop in pipeline?

Last edited:
Staff Emeritus
Homework Helper
It's worth a shot. Remember, pressure is in units of bars.

noname91
air compressor Q=2,6m^3/min D(diameter)=50mm P(pressure)=7,5Bar

V=Q/A ---> V=4*(2,6/60)/(3,14*0,05^2)

V=22,08m/s MACH=22,08/340=0,064

Can i use incompressible flow equations(DARCY-WEİSBACH)?