Pipe Flow Calculations Forum

Good Afternoon

Re the Online Pressure Drop and flow rate calculator

Just need some guidance to navigate around this most useful tool

My usual scenarios/requirements are to:

1) Calculate flow from a hydrant or other fitting (hose/tap etc) x metres from a gravity supply tower knowing the head (top water level from ground) pipe material, pipe length and pipe diameter. (which may or may not alter between tower and final flow point) - FLOW Q REQUIRED see example 1 below
2) Calculate static pressure at hydrant assuming flow at Hydrant is known- PRESSURE P2 REQUIRED see example 2 below
3) The same but with a direct pumped system and no break tank

Example 1:
Flow at Hydrant or fitting Required ? l/s
Gravity Head at Tower: 35M (3.5Bar)
Length from tower to hydrant/fitting: 400 M
Pipe Diameter: 200mm for 100 M then 100mm for 300M
Material: Cast Iron – all pipe-work

Example 2:
Pressure at Hydrant/Fitting Needed ? Bar
Flow at Hydrant/Fitting: 5 Lit/s
Gravity Head at Tower: 35M (3.5Bar)
Length from tower to hydrant/fitting: 400 M
Pipe Diameter 200mm for 100 M then 100mm for 300M
Material Cast Iron: – all pipe-work



Most grateful for your guide

I think most of your questions can be solved using pressure drop calculator.

Here is report for 100 mm 300 m long pipe

Pipe pressure drop calculator

1. volume flow rate (q):
q : 26.829168 l/s

3. pipe length (L):
L : 300 m

4. pipe diameter (D):
D : 100 mm

6. density (ρ):
ρ : 1000 kg/m3

7. kinematic viscosity (ν):
ν : 1.006 mm2/s

10. velocity (V):
V : 3.4159958 m/s

12. friction coefficient (f):
f : 0.01961603

13. Reynolds number (Re):
Re : 339562.2

15. pressure on the pipe start (p1):
p1 : 45 mWS

16. pressure on the pipe end (p2):
p2 : 10.0 mWS

17. pressure drop (p1-p2):
p1-p2 : 35 mWS

This calculations is assuming that you have constant diameter from start to end. As you said that diameter is changing you should calculate for each segment of pipe but this calculator is not enabled for it.

This is also the case with your second example.

Hi, how can I increase the pressure, of air flow through a pipe, from 6 Pa to around 1500 Pa? Thank you.

You can either use ventilator or increase pipe diameter to reduce pressure drop but it should be checked

Liked the thread.. I think pressure drop calculator is an effective instrument for air pressure measurement.

Yes, you should use pressure drop calculator.