Under what condition does the Hydraulic Pressure Relief Valve open?

The hydraulic pressure relief valve is designed to protect the hydraulic system from excessive pressure that could cause damage to components or compromise system integrity. It opens automatically when the system pressure exceeds a predetermined threshold, which, in this case, is specified as 1650 PSI.

This automatic actuation ensures that the hydraulic system remains within safe operational limits by venting excess pressure, thus preventing potential failures or safety issues. The valve senses the system pressure continuously, and when it surpasses 1650 PSI, it opens to release fluid and mitigate the pressure buildup. This behavior reflects a crucial safety mechanism that is vital for aircraft operation, as maintaining proper hydraulic pressure is essential for flight control systems and overall aircraft functionality.

In contrast, other options describe conditions that either do not trigger the valve or represent manual intervention, which is not how hydraulic pressure relief valves typically operate.