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Common leak detection methods of helium mass spectrometer based on helium mask method and injection method

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This paper introduces two leak detection methods of helium mass spectrometer: helium cover method and injection method.

1. Helium mask method

The helium cover method is to use a test cover to wrap the inspected piece. During leak detection, the air in the cover is removed first, and then the helium gas of 100KPA is filled. When the output indication of the leak detector changes, it indicates that there is a leak in the part under the helium cover. The inspection cover can be made of plastic film. For large quantities of small parts, special rigid inspection cover can also be made to make the pressure of the leakage gas filled is higher than 100KPA, so as to improve the leak detection sensitivity.

2. Injection method

Injection method is the most commonly used and convenient leak detection method. During leak detection, the nozzle connected to the cylinder containing helium is used to inject the suspected leak. The following problems should be paid attention to in leak detection by injection method:

(1) Leak detection sequence: from the top to the bottom of the inspected part, from the place close to the leak detector to the place far away from the leak detector, the injection shall be carried out point by point.

(2) In the initial inspection, a large diameter nozzle is used to make the coverage area of helium flow larger. After finding out the area where the leak is, use a small diameter nozzle to determine the exact location of the leak.

(3) First repair the detected large leak (seal with vacuum mud), and then detect the small leak.

(4) When there are two suspicious leakage points close to each other, one point should be covered first, and then the thinnest nozzle should be used to blow another point.

(5) When the nozzle injects a certain point, if the indicator of the leak detector changes, but the rising speed is slow and the indication value is very inconsistent, it indicates that there is a big leak in other places nearby.

(6) After the leakage is detected, it should be retested several times.

Generally, the total leakage rate is measured first, and then the leak location is carried out only when the total leakage rate exceeds the allowable value. The environment for leak detection shall be well ventilated, clean and dry without strong electromagnetic interference and vibration. The ambient temperature shall be (23 ± 7) ℃. Temperature and atmospheric pressure monitoring devices shall be provided on site.

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