Which of the following is the only type of pump that can be operated against a closed valve?

A centrifugal pump is the only type of pump that can operate against a closed valve due to its design and operating principles. It generates pressure by converting rotational energy, typically from a motor, into kinetic energy in the fluid being pumped. This kinetic energy is then converted to pressure as the fluid exits through the pump's discharge.

When a valve is closed, the centrifugal pump can still continue to run, and it will create pressure in the system until either the pump reaches its shutoff head or the pump is damaged due to excessive pressure. This characteristic allows centrifugal pumps to function effectively in systems where flow rates can be restricted or when encountering closed valves.

In contrast, other types of pumps such as vertical turbine pumps, axial-flow pumps, and mixed-flow pumps are not designed to operate effectively under such conditions. They rely on specific flow dynamics that are disrupted when faced with a closed valve, making them unsuitable for operation against it.