What is the location and purpose of the balance drum on a centrifugal compressor?

• A. It is on the discharge end of the shaft and is referenced to surface pressure to minimize thrust.
• B. It is on the suction end of the shaft and helps regulate flow.
• C. It stores lubricating oil for the bearings.
• D. It measures shaft speed.

Answer: (A)

The balance drum is used to counter the axial thrust produced by the compressor impeller. It sits on the discharge end of the shaft and is pressurized by the discharge gas, so the pressure acts on a surface inside the drum to oppose the thrust. This balancing action reduces bearing loads and helps keep the rotor stable during operation.

Stating why the other ideas don’t fit: placing the drum on the suction end wouldn’t provide balancing against the high-pressure thrust, storing lubricating oil is the job of an oil reservoir rather than a balance drum, and measuring shaft speed is done by a sensor, not a balance drum.