How is proper operation of a spray valve indicated when it is closed?

The proper operation of a spray valve being closed is indicated when the gauge shows low negative PSI. This occurs because when the spray valve is closed, the system is not delivering any spray material, leading to a drop in pressure within the system. In an ideal situation, this would cause the pressure to indicate a negative or very low positive reading, either reflecting an absence of pressure or a slight vacuum in the system.

Having the gauge show high positive PSI would indicate that the system is still under pressure, which would typically occur when the spray valve is open and the pump is active. No pressure reading could suggest a malfunction or an entirely closed system that isn't able to register any pressure, but it doesn't specifically indicate proper valve closure. Fluctuations on the gauge typically result from varying pressure levels due to opening and closing valves, or other malfunctions, not from the valve being effectively closed. Thus, the correct response effectively communicates an understanding of how pressure readings are related to the operation of a closed spray valve in aerial application practices.