What is the purpose of an impeller?

• A. Speed up liquid; increase velocity of gas, then convert to pressure and a volute
• B. Filter debris from the steam
• C. Reduce gas velocity to avoid noise
• D. Store energy for later release

Answer: (A)

The impeller’s job is to transfer mechanical energy into the fluid by increasing its velocity, and then use the surrounding volute (or diffuser) to convert that higher velocity into higher pressure at the discharge. As the impeller spins, fluid is flung outward, gaining velocity; the volute gathers this fast flow and slows it, turning kinetic energy into pressure. That’s why speeding up the liquid and then converting that velocity to pressure with the volute is the correct description.

Filtering debris isn’t the function of an impeller—that’s what filters or screens do. Reducing velocity to lessen noise isn’t the primary purpose of the impeller, since it’s about energy transfer, not damping. Storing energy for later release isn’t what an impeller does either; energy storage is the role of devices like flywheels or tanks.