If a centrifugal pump is located above the water level, what must be provided on the suction piping to hold the prime?

• A. Check Valve
• B. Gate Valve
• C. Air Valve
• D. Foot Valve

Answer: (D)

When a centrifugal pump sits above the water, the suction line tends to lose prime because water can drain back toward the source when the pump stops. To prevent that, you place a device at the end of the suction line that only allows water to flow toward the pump and prevents backflow. This is a foot valve, a type of check valve with a strainer that sits at the end of the suction line and remains submerged in the source. It keeps a water column in the suction piping, so priming is retained and the pump starts quickly again. Gate valves isolate, but don’t hold prime; an air valve would let air in and break prime; a general check valve at the wrong spot isn’t as effective as a foot valve for maintaining suction prime.