Why is it important for the MPO to close the tank fill valve during calculations?

Closing the tank fill valve during calculations is essential to ensure accurate flow readings. When the tank fill valve is open, it allows water to enter the system, which can skew the measurements and calculations. The flow readings must reflect the actual discharge rate of the pump and not be influenced by any additional water being introduced from the fill tank. By closing the fill valve, the operator can isolate the flow being generated by the pump, providing a precise measurement of how effectively the pump is working and ensuring that the calculated flow corresponds to the water that is being delivered to the intended location. This is crucial for operational efficiency and for future calculations regarding water supply and fire flow demands.