What factors contribute to suction losses in a pump system?

• A. Discharge line friction
• B. Suction line friction
• C. Ambient temperature of the surroundings
• D. Motor load

Answer: (B)

Suction losses come from energy being used up as the liquid moves toward the pump on the suction side. The main factor is friction in the suction line, where the fluid rubbing against the pipe walls dissipates energy and lowers the pressure available at the pump eye. This friction loss grows with longer piping, smaller diameter, rougher interior surfaces, higher flow rate, and any bends, valves, or fittings that add local losses. The result is reduced suction head and a smaller Available Net Positive Suction Head, which can lead to cavitation if insufficient.

Discharge line friction isn’t part of suction losses—the energy loss occurs after the pump, in the discharge piping. Ambient temperature isn’t a direct hydraulic loss in the suction path (though it can affect liquid viscosity and vapor pressure, influencing NPSH, it doesn’t add suction-side friction losses itself). Motor load relates to the pump’s mechanical power draw, not the hydraulic energy losses in the suction line.