Total Dynamic Head
Also known as TDH · pump head required
Worked example: 30 m TDH less 2400 cm static and 0.4 m velocity → 5.6 m friction — press Try an example to run it live, then adjust anything.
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UniversityFluid Mechanics, HVAC & Refrigeration
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Total Dynamic Head explained
Total dynamic head is the pump's job description in a single number. Lift the water 85 ft, lose 22.5 ft pushing it through the pipe, and hand it over with 1.5 ft of velocity head still on board, and the pump must produce 109 ft. Every pump selection begins here: TDH sets the y-coordinate of the duty point, design flow sets the x-coordinate, and the curve that passes closest to that point through its best-efficiency region wins the job.
The recurring mistake is measuring static head from the pump instead of between the two liquid surfaces. If the supply tank is flooded above the pump, that submergence subtracts from static head — a fact worth real money on a long transfer line. And do not double-count: many engineers fold velocity head into the friction allowance, which is fine for water systems where it is a fraction of a foot, but sloppy on high-velocity or short-run systems where it can be several percent of the total.
Total Dynamic Head formula
- = Total dynamic head (m)
- = Static head (m)
- = Friction head (m)
- = Velocity head (m)
Missing one of these? Work it out first, then come back
- Total dynamic head — Pump Water Horsepower, Pump Brake Horsepower
- Static head — Pump System Curve, Net Positive Suction Head Available (NPSHa)
- Friction head — Net Positive Suction Head Available (NPSHa), Hazen–Williams Head Loss
- Velocity head — Velocity Head (h = v²/2g), Pump Water Horsepower
Pump power and efficiency
7 formulasWater horsepower, brake horsepower, pump efficiency, NPSH available and specific speed — sizing the motor and keeping the impeller wet.
Heads in a piping system
6 formulasPressure head, velocity head, static fill pressure and total dynamic head — the feet of water a pump and a gauge are each talking about.