Pump capacity is rated according to flow rate and dynamic head. Which type of head is specified in this rating?

• A. Suction head
• B. Suction lift
• C. Total head
• D. Discharge head

Answer: (C)

When a pump’s capacity is specified, it’s given in terms of how much fluid it can move at a certain head. That head isn’t just a single side condition like suction or discharge; it’s the total energy the pump must add to the fluid to push it through the entire system. This is the total dynamic head.

Total dynamic head combines three things: the static head (the change in elevation the fluid must overcome), the friction losses in the piping (pipes, fittings, valves that waste energy as flow moves), and the velocity head (the energy associated with the flow’s speed). The pump curve is built around flow rate versus this total head, so you know how much flow you can get at a given system energy requirement.

Suction head and suction lift relate only to conditions on the suction side and don’t represent the full energy the pump must supply. Discharge head refers to energy on the discharge side, but without summing all losses and elevation changes, it doesn't capture the entire requirement. That’s why total head is the correct descriptor for the rating.