What pressure rate must you establish before setting the pressure relief control on the 90AF-4 refueling flow control?

Establishing the correct pressure rate is crucial for the safety and efficiency of the refueling process. The appropriate choice indicates that the pressure relief control for the 90AF-4 refueling flow control should be set 5 psi above the normal downstream pressure. This setting allows the system to effectively relieve excess pressure that could potentially lead to system failures or unsafe conditions during operation.

Setting the pressure relief control at this level ensures that the control mechanism engages before the downstream pressure reaches a critical threshold, providing a buffer zone that helps maintain system integrity. By opting for a setting of 5 psi, you create an ample safety margin, which not only accommodates normal fluctuations in pressure but also helps to prevent potential bursts or failures in the system.

In contrast, lower pressure settings, whether they are 2-3 psi above upstream or downstream, may not provide enough of a buffer to safeguard against spikes in pressure, leading to a higher risk of operational mishaps. Therefore, the choice to set it at 5 psi above normal downstream pressure is the most effective approach for maintaining safety and functionality in the refueling operation.