Engagement and disengagement is accomplished by flipping a lever on the bottom of the unit. In the picture that you see it ‘open’ in my hand, you’ll see two silver dots; one on the lever and one on the body. These are magnets that hold the lever in place when it’s closed and “on.” They are pretty strong and there has been no issue with them holding onto each other. When you close the lever, it cantilevers the pin that depresses the valve pin on your tank. This is also the ASA’s bleed system. When the marker’s charged with air, flip the lever into its ‘open’ direction to bleed the air from the system.