What is the purpose of an intake relief valve on some systems?

• A. To prevent pump from drawing more water than supply and help maintain prime; ensures smooth flow and avoids vacuum.
• B. To release air
• C. To increase pressure beyond nozzle pressure
• D. To regulate engine speed

Answer: (B)

An intake relief valve on the suction side is there to vent trapped air and prevent vacuum from forming in the suction line so the pump can prime properly. When you start the pump, air in the suction path can create a partial vacuum that makes it hard for water to reach the impeller, risking loss of prime or cavitation. The intake relief valve opens to let that air escape; as water fills the line and prime is established, the valve closes to keep air from reentering. This keeps the pump pulling water smoothly rather than fighting air pockets.

It isn’t intended to release air on the discharge side, it doesn’t boost pressure beyond what the system is designed to handle, and it doesn’t regulate engine speed.