Second, mechanical products generally use airtight detectors to conduct tightness test, i.e. all sealing nozzles of the products are manually or automatically blocked, test gas enters the workpiece through the test instrument for testing, then pressure changes are judged by sensors in the instrument, and finally whether leakage occurs or not is judged.  All such products will have accurate calculation formulas and data comparison, and have different standards according to the requirements of different products.

Through comparison, we can know that the water inspection method is low in cost, but it is only identified by human eyes, and there will be missed inspection. In addition, it will cause damage to some workpieces, such as rusting and corrosion of metal parts, and some workpieces will be dried after water inspection, but it is easier to detect which part of the workpiece leaks.  Instrument detection cost is high, but the operation is relatively simple and efficient, especially for small workpieces.  Generally, there will be no misjudgment and no damage to the workpiece. The disadvantage is that only leakage can be detected and no specific leakage can be detected. The CQI inspection will do  random sampling   on basis of the product characteristics,  and flexible selection of the corresponding tightness test method.