What is the principle of automatic nail suction of riveting gun?

Well, at the front end of the barrel of the pneumatic riveting gun, there is a small pipe. This pipe fitting is hollow, but there is a step at the head. After plugging in, the air will only go back, so the compressed air will only be sprayed back under the action of this pipe fitting. Because the air pressure in front of the barrel is relatively small, it will generate suction, so if there is a rivet near the nozzle, it will be sucked in.