FAA AMT Airframe Practice Exam 2025 – All-in-One Study Guide to Master Aviation Maintenance Technician Certification!

In a pneumatic deicing system, the suction relief valve regulates the vacuum of the air pump to hold the deicing boots deflated when the system is turned off. This valve ensures that there is no excessive vacuum buildup that could damage the deicing boots or other components of the system.

Option A, the heat control relay, is responsible for regulating the heat output in systems like engine anti-ice systems but does not regulate the vacuum for deflating the deicing boots.

Option B, the vane type pump, is responsible for generating the vacuum required for the operation of pneumatic systems but does not regulate it to hold the deicing boots deflated when the system is off.

Option D, the distributor valve, directs the flow of air or fluid within a system but does not specifically regulate the vacuum for holding the deicing boots deflated when the pneumatic deicing system is off.

Therefore, the correct answer is option C, the suction relief valve, as it specifically controls the vacuum to keep the deicing boots deflated when the system is not in use.