In centrifugal pumps, what is the primary purpose of a diffuser ring or the volute acting as a diffuser?

• A. Increase flow rate
• B. Reduce noise
• C. Improve efficiency
• D. Convert high velocity to pressure

Answer: (D)

The main idea here is energy recovery: the diffuser ring or volute is designed to turn the fluid’s velocity into pressure. When the impeller throws fluid out at high speed, the surrounding diffuser provides a gradual expansion that slows the flow. As velocity decreases, static pressure rises (that's the velocity head converting to pressure head). This increases the discharge pressure and helps the pump operate more efficiently by using the kinetic energy rather than letting it remain as high-speed fluid. It’s not primarily about forcing more flow into the system or reducing noise; the central function is converting that high velocity into usable pressure energy, which is why this choice is best.