A truck operating from draft with a lift of 6 meters has an approximate efficiency of what percent of its rated capacity?

• A. 40%
• B. 60%
• C. 80%
• D. 50%

Answer: (B)

Drafting from a static water source forces the pump to create suction to lift water up to the pump. The farther the lift, the more suction head the pump must develop and the more friction losses occur in the suction hose, valves, and fittings. These suction losses reduce the flow the pump can deliver on the discharge side. For a lift of about 6 meters, a practical rule of thumb is that the pump will deliver roughly 60% of its rated capacity. That 60% accounts for the suction head and friction losses while keeping some margin before cavitation or further drops in performance as lift increases. If the lift were greater, the percentage would drop further; if the lift were smaller, the flow would be closer to the rated capacity.