For a 3500-gallon pump, the circulating (casing) relief valve size is ______.

• A. 1/2 inch
• B. 2 inch
• C. 3/4 inch
• D. 1 inch

Answer: (D)

Circulating (casing) relief valve serves as a bypass from the pump casing back to the suction to keep the pump from overheating when the discharge is blocked or not delivering flow. The size is chosen to allow enough bypass volume to cool and lubricate the pump without wasting flow or creating pressure issues in the rest of the system. For a pump of this size, a 1-inch valve provides the right balance: it allows sufficient bypass to protect the pump while not unduly robbing flow when the pump is delivering water. A valve that’s too small would not relieve enough and risk damage; a valve that’s too large would bypass too much flow and affect system efficiency. So the appropriate circulating relief valve size is 1 inch.