The level of the fluid that is being pumped is below the center line of the pump?

• A. Static lift
• B. Suction lift
• C. Discharge head
• D. Negative suction head

Answer: (D)

Suction head is defined by the vertical position of the liquid surface relative to the pump’s centerline. When the liquid surface sits above the centerline, the suction head is positive because the weight of the liquid helps push it into the pump. If the liquid level is below the centerline, the pump has to lift the liquid upward and the pressure at the suction falls below atmospheric, giving a negative suction head. This scenario describes a negative suction head, since the suction pressure is below zero gauge relative to atmospheric. The term highlights the sign of the suction requirement, whereas other terms like static lift or discharge head refer to vertical distances or pressures on the discharge side, not the suction-side pressure sign.