Which pump type is used as a priming pump in typical operations?

• A. Diaphragm
• B. Centrifugal
• C. Rotary gear
• D. Piston

Answer: (C)

When starting a centrifugal fire pump, you must first remove air from the suction line and fill it with water to establish a prime. A positive-displacement device that can generate a steady, controlled flow is ideal for this task, and a rotary gear pump fits that role perfectly. Its gear-type design delivers a consistent, low-flow output with enough suction to pull air out of the suction line and push water into the pump, allowing the prime to form even against the initial suction head. This makes it reliable for establishing the prime quickly and maintaining it as the main pump comes up to speed.

Other pump types don’t couple as well with the priming requirement. A centrifugal pump is the main workhorse and needs a prime to start, but it isn’t suited to priming because it relies on water already in the suction to create flow, not to evacuate air. Piston and diaphragm pumps can be used in some priming arrangements, but they’re typically less compact, more maintenance-intensive, or less consistent for continuous priming tasks. The rotary gear pump’s combination of reliable prime creation, compactness, and smooth operation is why it’s used as the priming pump in typical operations.