The vacuum suction truck uses a vacuum pump to evacuate the tank and then uses atmospheric pressure to press sewage into the tank. Normally the vacuum suction truck will be equipped with an anti-overflow valve. The anti-overflow valve can prevent the tank from being pumped to a certain extent. But because the principle of the anti-overflow valve is to connect the air inside and outside the tank after being floated by the sewage, so that the air pressure can be balanced, and the vacuum environment can be destroyed to prevent the full suction effect. There is no sound in actual use. If you do other things and don’t pay attention when suctioning sewage, it will lead to flooding. Because after the anti-overflow valve of the sewage suction truck is opened, it will take time for the air pressure inside and outside the tank to balance, about a few seconds. It may have filled the tank in a few seconds. And if it is working at high power, the air flowing into the tank from t...