How many seconds must the flow rate stay above 700 gpm through the Type 4 return venturi before the second pump is called off?

The correct answer is determined by the operational requirements for maintaining effective fuel system management. In the case of a Type 4 return venturi system, a flow rate must remain above a specific threshold—in this instance, 700 gallons per minute (gpm)—for a duration that ensures proper operational stability and safety.

Specifically, a sustained flow over 700 gpm for at least 15 seconds allows enough time for the system to confirm that there is a reliable supply and demand balance before the second pump is deactivated. This period serves as an operational safeguard, ensuring that fluctuations in flow can be accounted for and that the system does not inadvertently stall or compromise overall performance.

By maintaining the flow rate for at least this duration, the system can effectively assess whether the return venturi is functioning properly and whether all safety protocols are being met, thus supporting optimal system efficiency and operational reliability.