Total dynamic head is the total pressure when fluid is moving through a system which includes the pressure needed to overcome elevation differences and the pressure needed to overcome friction losses in order to produce a required pressure output. This measurement is usually expressed in either feet or meters, and refers to the equivalent height of the column of fluid in a manometer.
The total dynamic head is comprised of two parts, the static head and the friction head. The static head is the actual vertical difference measured from the minimum fluid level at the basin to the highest point of the discharge pipe. The friction head is the additional head created due to the resistance of flow of the fluid within the system due to its components and is a function of the friction factor, the length and diameter of the pipes and the velocity at which the fluid flows. The friction factor itself can vary due to the material of the pipes as well as the components in the system, such as elbows, valves and filters. The formula for the total dynamic head is derived from Bernoulli's extended equations and is useful for determining the size and power of the pump required for the system.