Florida Wastewater Practice Test

What type of pump can cause major damage if started against a closed valve?

1. Submersible pump

2. Positive displacement pump

3. Centrifugal pump

4. Diaphragm pump

The correct answer is: Positive displacement pump

A positive displacement pump is designed to move a specific volume of fluid with each cycle or motion. When a positive displacement pump is started against a closed valve, it continues to attempt to push the fluid through the system. Since the pump is displacing a fixed amount of fluid regardless of the pressure in the line, this can lead to an excessive build-up of pressure. If the pressure becomes too high, it can cause serious damage to the pump, the piping, and any connected equipment. This situation could result in leaks, ruptures, or complete mechanical failure. In contrast, submersible pumps and centrifugal pumps typically manage pressure more effectively in these situations. Centrifugal pumps, for example, will generally not cause damage against closed valves as they have inherent characteristics that allow them to handle such conditions—specifically, they can stall and not create excessive pressure build-up. Diaphragm pumps also have specific tolerances and fail-safes built into their operation, minimizing the risk of damage in cases where flow is restricted. Thus, the unique operating principles of positive displacement pumps make them particularly vulnerable to the dangers of starting against a closed valve.