PRACTICAL FORMULA
TDH = static head + pressure-head difference + friction and equipment losses.
Calculate every term at the design flow and use one consistent unit system. If source or destination pressure changes, calculate the important minimum, normal and maximum conditions rather than giving one unsupported head value.
Static head comes from liquid levels, not pipe length
For open source and destination vessels, static head is the vertical difference between the relevant liquid surfaces. A long horizontal pipe can add substantial friction but does not add static elevation. When tank levels vary, select the levels that create the operating cases the pump must handle.
For a pump taking suction below the source level, the available static suction can reduce the net lift term. For a source below the pump, suction lift increases the duty and must also be checked against priming and inlet-pressure limits. Draw a simple elevation sketch before calculating.
Convert pressure difference into head carefully
If the receiving vessel or process header is pressurized, the pump must overcome that required pressure in addition to elevation and losses. If the source vessel is also pressurized, its pressure contributes to the inlet condition. Use the pressure difference across the complete system.
Pressure and head are related through liquid density. The same pressure corresponds to a different liquid head when density changes. Therefore provide the liquid and specific gravity when known; do not copy a water conversion into a different process liquid without checking it.
Friction depends on flow
Include losses in straight pipe, elbows, tees, reducers, valves and entrances. Add equipment losses through filters, heat exchangers, meters, nozzles and other process components. Obtain vendor pressure-drop data at the intended flow where equipment creates a significant restriction.
| Input | Why it matters |
|---|---|
| Pipe internal diameter and length | They establish velocity and straight-pipe friction. |
| Fittings and valves | Each adds local resistance. |
| Liquid viscosity and density | They influence pressure conversion and friction behavior. |
| Design flow | Loss increases as flow increases; calculate at each important case. |
| Equipment pressure drop | Filters and process devices may be a major part of TDH. |
Add only real system losses. An arbitrary margin can move the selected operating point away from the system requirement. If uncertainty remains, show it as a range and explain which input needs confirmation.
A quotation-ready head worksheet
- State liquid, temperature, density or specific gravity and viscosity where relevant.
- State minimum, normal and maximum required flow.
- Draw source and destination levels, including their operating ranges.
- Record source and destination pressures.
- List pipe sizes, lengths, fittings and valve types.
- Add pressure drop for filters, exchangers and process equipment at each flow.
- Calculate TDH for the important operating cases.
- Send the calculation and layout with the inquiry.
The resulting duty point helps Shangcheng compare the appropriate family—from inline centrifugal pumps to CDLF multistage pumps—but liquid compatibility, suction conditions and installation still require review. See the general pump selection guide before requesting an exact model.
Send the calculation, not only a pipe size.
Email liquid, flow cases, elevations, pressures, piping and equipment losses to shscpv@gmail.com.
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