Which of the following is NOT a part of preparing an emergency oxygen system for service?

Keeping the regulator pressurized is not part of preparing an emergency oxygen system for service because a properly functioning oxygen system does not require the regulator to be in a constant pressurized state before use. The regulator is designed to maintain pressure only when the system is activated and in use. Pressurization of the regulator can result in unnecessary wear or damage if the system is not handled properly.

On the other hand, checking the flow meter for functionality, ensuring adequate oxygen supply, and inspecting for any signs of leaks are critical steps in the preparation of an emergency oxygen system. These actions ensure that the equipment will operate correctly in an emergency situation, providing the necessary flow of oxygen to the person in need. Regular checks and maintenance help ensure the safety and efficacy of the system when it is called into action.