Keep water-like liquids at 1-2.5 m/s, suction below discharge velocity, and confirm regime with Reynolds before any loss calculation.
Velocity limits by service
Suction 0.8-1.5 m/s protects pump inlet conditions; discharge 1.5-2.5 m/s balances cost against loss; long transfers near 1 m/s avoid water hammer margins eroding. Gases and steam run an order of magnitude faster and follow their own service tables.
What overspeed costs
Head loss scales with v squared, so 3 m/s instead of 1.5 m/s costs roughly four times the pumping energy plus erosion, noise, and vibration. Resize the line rather than accepting chronic overspeed.
Confirm regime with Reynolds
Re = rho v D / mu decides laminar, transitional, or turbulent flow. No friction number is trustworthy until the regime is known, so run the Reynolds check first.
Formulas
Mean velocity
v = Q / A
Q in m3/s, A in m2.
Diameter from velocity
D = sqrt(4Q / (pi v))
Round up to the next standard DN.
Worked example
36 m3/h at 1.5 m/s
Inputs: Q 36; target 1.5.
Calculation: Required ID 92.3 mm, so select DN100 at 1.27 m/s.
Frequently asked questions
What velocity should I target?
1-2.5 m/s for water-like liquids; suction lower than discharge.
What if velocity exceeds 3 m/s?
Roughly 4x the loss for 2x the velocity. Resize the line.
When do I need Reynolds?
Always before any loss calc: Re decides laminar vs turbulent.
Sources and further verification
- Reynolds number — Wikipedia
- Bernoulli's principle — Wikipedia
Next step