What element of the primary hydraulic system activates the corresponding actuator when lowering the flaps?

The element of the primary hydraulic system that activates the actuator when lowering the flaps is the electrical selector valve. This valve plays a critical role in directing hydraulic fluid to the actuator responsible for moving the flaps. When the pilot commands flap extension, the electrical selector valve is activated, allowing hydraulic fluid to flow through the system to the specific actuator, which then extends the flaps to the desired position.

Understanding the operation of the electrical selector valve is essential because it ensures that the hydraulic pressure is appropriately channeled to the actuator based on pilot input. This action is vital for the safe and efficient operation of the aircraft's flap system during various phases of flight.

The other elements listed serve different functions within the hydraulic system and do not directly activate the flap actuator. The hydraulic reservoir provides the fluid necessary for the system but does not control the flow. The pressure release valve plays a role in the management of hydraulic pressure but does not initiate flap movement. Actuator return refers to the mechanism that allows the actuator to return to its neutral position after movement, rather than initiating the flap lowering process. Understanding these distinctions clarifies why the electrical selector valve is the key component in this scenario.