Total dynamic head, or TDH, describes the total head a pump must provide at an identified operating flow. Head expresses fluid energy in an equivalent height, commonly shown in feet on a water-pump specification. It includes the system's elevation or pressure requirements and flow-dependent losses, rather than just the vertical height of a pipe.
Total dynamic head, or TDH, describes the total head a pump must provide at an identified operating flow. Head expresses fluid energy in an equivalent height, commonly shown in feet on a water-pump specification. It includes the system's elevation or pressure requirements and flow-dependent losses, rather than just the vertical height of a pipe.
Vertical lift is only part of the requirement
Moving water to a higher discharge point requires head. Piping, fittings and other components also resist the flow. Those losses change with flow rate, pipe dimensions and the actual layout.
The check-valve cracking pressure entry distinguishes a valve opening threshold from its losses at an operating flow.
Zoeller's sewage-pump sizing guidance distinguishes vertical lift from total dynamic head. The Department of Energy's pumping-system sourcebook also explains how the system requirement and pump performance have to be evaluated together. The sourcebook covers broader pumping systems; it is not approval of a particular household sewage installation.
The suction and discharge conditions matter. A designer needs to identify the relevant elevations, pressures and loss terms rather than simply measure the highest visible pipe and call that the complete TDH. For a separate suction-pressure assessment, see pump cavitation.
A pump rating is tied to flow
A pump does not deliver every advertised flow at every head. Its performance curve relates flow to the head it can develop for the stated model and configuration. The installed operating point depends on where that capability meets the system requirement.
A maximum-flow label and a maximum-head label normally describe different points, not a simultaneous promise. Horsepower alone also does not identify the delivered flow. Two different pumps can behave differently on the same pipe route.
The correct evaluation additionally accounts for the handled fluid, solids, operating limits and installation conditions. A TDH calculation cannot make an unsuitable pump type appropriate for sewage or another application. The best efficiency point entry explains another chart term to evaluate with those operating limits.
Reading a replacement recommendation
Ask which operating flow and system head were used to choose the model. The proposal should identify the assumed route, discharge condition and relevant loss calculations, including any uncertainty in the existing system.
Our pump curve entry explains the chart. The sewage ejector pump entry explains that equipment's role. TDH helps assess selection; it does not diagnose a failed pump or guarantee an installed result without the required design and commissioning evidence.