Which statement about the propeller vane arrangement is true?

• A. They are curved toward the direction of rotation
• B. They are straight blades
• C. They are curved away from the direction of rotation
• D. They are not used in firefighting pumps

Answer: (C)

Backward-curved propeller vanes are shaped so the blade curvature bends away from the direction the wheel is turning. This arrangement is chosen because it maintains smoother flow and higher efficiency over the operating range firefighters rely on, while also reducing unwanted radial forces on the shaft. It helps the pump deliver large flows against pressure with stable performance. Blades curved toward the direction of rotation (forward-curved) tend to produce higher flow losses and greater load variation, and straight blades don’t optimize the fluid dynamics for high-discharge firefighting pumping. These vanes are indeed used in firefighting pumps, making the backward-curved, curved-away-from-rotation option the true statement.