A properly functioning positive cutoff valve should supply what pressure to the boom and nozzles when the spray flow is stopped?

A properly functioning positive cutoff valve is designed to maintain a consistent positive pressure in the system when spray flow is stopped. When the valve is closed, it prevents any backflow or loss of pressure, which is critical for the effectiveness of the aerial application system. This feature ensures that when the operator decides to spray again, the system can immediately deliver the correct amount of liquid without delay or pressure drop.

Maintaining high positive pressure in the boom and nozzles when the spray is not flowing helps prevent any blockages that could occur from residual materials settling in the lines. It also ensures that any subsequent activation of the system will result in a precise and reliable spray pattern, crucial for effective application.

The other options lack the consistency or reliability needed for a proper spraying operation. Zero pressure would mean that there is no liquid available to be sprayed when needed. Negative pressure could cause undesirable suction effects, making it harder to control the system. Variable pressure would lead to inconsistent application characteristics, not suited for the precision often required in aerial applications.