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How to check the sealing of the VHP pass box?
How to check the sealing of the VHP pass box?1. Visual inspection method1. Visual inspection - Close the door of the pass box and carefully observe the gap between the door and the door frame. Under normal circumstances, there should be almost no obvious gap. If you can see obvious light coming in, or if you can insert an ordinary A4 paper (paper thickness is about 0.1mm), this indicates that there may be a problem with the seal. For example, in the pass box of some pharmaceutical workshops with extremely high cleanliness requirements, even a tiny gap may allow external dust and microorganisms to enter, affecting the quality of drugs. - Check the status of the sealing strip. The sealing strip is one of the key components to ensure the sealing of the pass box. Check whether the strip has signs of falling off, aging, deformation, or damage. Aging sealing strips may become hard, brittle, lose elasticity, etc., so that they cannot fit tightly against the door frame and door, resulting in reduced sealing. 2. Smoke test method (simple operation) - Prepare a tool that can produce a small amount of smoke, such as an aromatherapy candle or a smoke generator (under the condition of ensuring safety and complying with the operating environment regulations). Light a candle or turn on a smoke generator on one side of the pass box to gather smoke on this side. - Close the door of the pass box and observe whether there is smoke on the other side. If obvious smoke leakage can be seen on the other side, it means that the pass box is not well sealed. This method is more intuitive, but care should be taken to avoid smoke pollution in the surrounding environment and equipment, especially in some laboratories or electronic production workshops that are sensitive to air quality. 2. Pressure test method 1. Positive pressure test - A pressure gauge and an air source that can generate positive pressure (such as a small air compressor) are required. First, connect the pressure gauge to the pressure test interface inside the pass box (if there is no special interface, it can be connected through a well-sealed vent). - Close all doors and windows of the pass box, use the air source to inject air into the pass box, and raise the internal pressure to a certain value, generally 10-50Pa higher than the external atmospheric pressure (the specific value can be determined according to the equipment manual or actual requirements). - Observe the changes in the pressure gauge reading. If the pressure drops rapidly in a short period (such as 1-2 minutes), it means that there is a leak in the pass box and the sealing is not good. The speed of the pressure drop can roughly reflect the severity of the leak. The faster the drop, the more serious the leak. 2. Negative pressure test - A pressure gauge and a device that can generate negative pressure, such as a vacuum pump, are also required. Connect the pressure gauge to the inside of the pass box. After closing all doors and windows, use a vacuum pump to extract the air inside the pass box to reduce the internal pressure to a certain value below the external atmospheric pressure, usually - 10 - - 50Pa. - Observe the pressure gauge reading. If the pressure rises rapidly, it indicates that there is a leak. This method can be used in combination with positive pressure testing to more comprehensively check the sealing of the pass box under different pressure conditions. III. Professional instrument detection method 1. Ultrasonic leak detector detection - Ultrasonic leak detector is a relatively professional detection equipment. Its principle is to use the high-frequency signal generated by ultrasonic waves at the leak to detect the leak point. Place the sensor of the leak detector on the surface of the pass box and move the sensor according to a certain scanning path. - When the leak detector detects an ultrasonic signal, it will sound an alarm or display the leak location on the display. This method can accurately locate tiny leaks and is very suitable for pass boxes with extremely high sealing requirements (such as pass boxes in electronic chip manufacturing workshops), but the instrument price is relatively high and operation requires certain professional knowledge. 2. Helium leak detection method (high-precision detection) - Helium leak detection is a high-precision sealing detection method. Helium is filled into the inside of the transfer window to a certain pressure. Then, a helium mass spectrometer leak detector is used to detect the outside of the transfer window. - Because helium molecules are small, light, and have an extremely low content in the air, the helium mass spectrometer leak detector has an extremely high sensitivity to helium. If a helium leak is detected, it can be accurately judged that the sealing performance of the transfer window is poor, and the leak location can be determined. This method is usually used in special environments with extremely high sealing requirements, such as pass boxes in aerospace equipment manufacturing workshops, but the detection cost is also high. |
