Pumps and Compressors Flashcards

What is the purpose of priming a centrifugal pump?

Answer: To fill the pump casing and suction line with liquid to displace air, since centrifugal pumps cannot pump air

Centrifugal pumps must be primed (filled with liquid) because they cannot create sufficient vacuum to lift liquid when filled with air. The impeller needs liquid present to function — it imparts energy to the liquid, not to air.

What are the signs of cavitation in a centrifugal pump?

Answer: Noise like pumping gravel, reduced flow and pressure, and erosion damage to the impeller

Cavitation produces a distinctive rattling or gravel-like noise as vapor bubbles implode. It causes reduced flow and head, pitting and erosion damage to the impeller vanes (especially the low-pressure sides), and increased vibration.

What is a gear pump and what type of fluid transfer is it used for?

Answer: A positive displacement pump using meshing gears to move fluid, used for viscous liquids and hydraulic systems

A gear pump is a positive displacement pump that uses two meshing gears to trap fluid between the gear teeth and the casing, carrying it from the suction to the discharge side. It is well-suited for pumping viscous fluids, oils, and hydraulic systems.

What is the function of a packing gland on a pump?

Answer: To compress packing rings around the shaft to control leakage while allowing slight dripping for cooling and lubrication

A packing gland uses the gland follower to compress soft packing rings around the rotating shaft to control leakage. A slight controlled drip is intentional — it cools and lubricates the packing. Over-tightening burns the packing and scores the shaft sleeve.

What is a diaphragm pump and what is its main advantage?

Answer: A positive displacement pump using a flexible diaphragm, capable of handling abrasive, viscous, and chemically aggressive fluids without contamination

A diaphragm pump uses a flexible membrane that reciprocates to displace fluid. Since the pumped fluid contacts only the diaphragm and check valves (no rotating seals or shaft penetrations), it excels at handling corrosive, abrasive, and shear-sensitive fluids with zero leakage.

What is the best efficiency point (BEP) of a centrifugal pump?

Answer: The flow rate and head at which the pump operates at its highest efficiency, with minimum vibration and longest life

The BEP is the operating point where the pump converts the most input energy into useful hydraulic output with the least waste. Operating at or near BEP minimizes vibration, radial bearing loads, cavitation risk, and component wear, maximizing pump life.