What happens when the tank fill valve is opened fully during pump operations?

When the tank fill valve is opened fully during pump operations, the governor on the fire apparatus treats it as an additional discharge. This means that the governor compensates for the flow being drawn from the tank to maintain the appropriate engine speed and pressure needed for effective pumping.

By considering the tank fill as another discharge, the governor adjusts the throttle to ensure the engine operates efficiently. This maintains a steady pressure in the system, allowing for proper operation of the hoses being used for firefighting or other purposes. The system is designed to manage the variable flows, ensuring that water is still available at the necessary discharge points while simultaneously replenishing the onboard water supply.

In contrast, when the tank fill valve is fully opened, the engine speed does not necessarily decrease significantly. Instead, the governor's adjustment helps stabilize the engine speed. Additionally, while it might seem that opening the tank fill could increase water flow to hoses or stabilize pressure, the primary mechanism at play is the governor’s response to manage the additional flow demand.