Pipe Flow Calculator

Calculate flow rate, velocity, and pressure loss in pipe systems

kg/m³
Pa·s

Pipe Properties

m
m
m
Typical values: PVC (0.0000015 m), Steel (0.00015 m), Concrete (0.0003 m)
m³/s
m/s
Pa

Understanding Pipe Flow Calculations

Flow Rate and Velocity

The relationship between flow rate (Q), velocity (v), and pipe cross-sectional area (A) is:

Q = v × A

For a circular pipe with diameter (D):

Q = v × π × (D/2)²

Where:

  • Q = Flow rate (m³/s or ft³/s)
  • v = Flow velocity (m/s or ft/s)
  • D = Pipe internal diameter (m or ft)

Reynolds Number

The Reynolds number (Re) determines whether flow is laminar or turbulent:

Re = (ρ × v × D) / μ

Where:

  • ρ = Fluid density (kg/m³ or lb/ft³)
  • μ = Fluid dynamic viscosity (Pa·s or lb/(ft·s))

Flow is generally:

  • Laminar when Re < 2000
  • Transitional when 2000 < Re < 4000
  • Turbulent when Re > 4000

Pressure Loss in Pipes

The Darcy-Weisbach equation calculates pressure loss due to friction:

ΔP = f × (L/D) × (ρ × v²/2)

Where:

  • ΔP = Pressure loss (Pa or psi)
  • f = Darcy friction factor
  • L = Pipe length (m or ft)

Friction Factor

For laminar flow (Re < 2000):

f = 64 / Re

For turbulent flow, the Colebrook-White equation is used:

1/√f = -2 × log₁₀(ε/3.7D + 2.51/(Re × √f))

Where:

  • ε = Pipe roughness (m or ft)

This is solved iteratively or using approximations like the Swamee-Jain equation:

f = 0.25 / [log₁₀(ε/3.7D + 5.74/Re^0.9)]²

Recommended Velocities

Fluid Type Service Type Recommended Velocity Range
Water Pump Suction 0.6 - 1.2 m/s (2 - 4 ft/s)
Pump Discharge 1.5 - 3.0 m/s (5 - 10 ft/s)
Distribution Lines 1.2 - 2.4 m/s (4 - 8 ft/s)
Air Compressed Air 6 - 30 m/s (20 - 100 ft/s)
Ventilation 3 - 10 m/s (10 - 33 ft/s)
Oil Hydraulic Systems 1.5 - 6.0 m/s (5 - 20 ft/s)

Pipe Roughness Values

Pipe Material Absolute Roughness (ε) Absolute Roughness (ε)
mm inches
Drawn Tubing (brass, copper, plastic) 0.0015 0.00006
PVC, Plastic Pipes 0.0015 - 0.007 0.00006 - 0.0003
Commercial Steel or Wrought Iron 0.045 - 0.09 0.0018 - 0.0035
Galvanized Iron 0.15 0.006
Cast Iron 0.26 0.01
Concrete 0.3 - 3.0 0.012 - 0.12

Common Pipe Flow Problems

Causes:

  • Pipe diameter too small for required flow rate
  • Excessive pipe length or unnecessary bends
  • High pipe roughness due to corrosion or scaling
  • Flow velocity too high

Solutions:

  • Increase pipe diameter
  • Reduce flow rate if possible
  • Clean pipes to reduce roughness
  • Redesign system with more direct routing

Causes:

  • Flow velocity too high (water hammer)
  • Air entrainment in liquid systems
  • Cavitation due to pressure drops
  • Resonance in the piping system

Solutions:

  • Reduce flow velocity
  • Install air eliminators
  • Redesign system to prevent low pressure areas
  • Add pipe supports or vibration dampeners

Causes:

  • Insufficient pressure head
  • Blockages or restrictions in pipes
  • Air locks in the system
  • Pump operating below specifications

Solutions:

  • Increase pump capacity or pressure
  • Clean or replace clogged pipes
  • Install air release valves at high points
  • Check pump performance and maintenance

Engineering Disclaimer

This calculator provides estimates based on idealized conditions and standard equations. For critical applications:

  • Consider additional factors such as minor losses from fittings, valves, and bends
  • Account for temperature effects on fluid properties
  • Consult applicable engineering codes and standards
  • Verify results with physical testing when necessary
  • Consult with a professional engineer for critical systems