Pipe Velocity Check
Sediment under 0.6 m/s, water-hammer over 3.0 m/s. The band check + inverse-diameter helper, in one quick page.
Inputs
Inverse: pick a diameter for a target velocity
How this works
The math is simple — what matters is the design rule. Plumbing codes typically design cold water around 5-7 ft/s. Hot water gets dropped 1-2 ft/s lower because erosion-corrosion of copper accelerates with temperature × velocity. Industrial process lines may push higher when the fluid and pipe lining permit.
Water hammer (a transient pressure spike from sudden valve closure) scales linearly with velocity via the Joukowsky surge ΔP = ρ·a·Δv. Above 3 m/s the energy in the moving column is high enough to damage copper joints, push past solenoid-valve closure ratings, and produce the telltale "knocking" that annoys building tenants. The full physics, math, and the three engineering fixes are in the water-hammer guide.
| ft/s | m/s | Reason | |
|---|---|---|---|
| Cold water (domestic) | 5-8 | 1.5-2.4 | Standard ASPE band |
| Hot water (≥ 50°C) | 3-5 | 0.9-1.5 | Erosion-corrosion of copper |
| Chilled water (HVAC) | 4-8 | 1.2-2.4 | Balance friction vs noise |
| Steam (low-pressure) | 25-50 | 7.6-15 | Vapor — different physics |
| Pump suction | 2-4 | 0.6-1.2 | Avoid NPSH pressure drop |
| Pump discharge | 5-10 | 1.5-3 | Above NPSH limit |