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Principles of Several Common Testing Methods for Air Tightness Tester

The air tightness tester, also known as the tightness tester, leak detector and leak detector, is an advanced nondestructive testing method. The product is judged by inflating, stabilizing and testing the product, and then the leak detection system obtains its pressure drop value and leakage rate based on a series of analysis, sampling and calculation. At present, the common test methods include direct pressure method (pressure method), differential pressure method, closed chamber method (quantitative method, volume method), flow method and mass flow method.

1、 Direct compression method

Direct pressure method, also called pressure method, is applicable to the test of workpieces with low precision or low pressure required for sealing test, IP65 waterproof test, etc.

Leakage detection principle: fill the chamber of the workpiece to be measured with gas of specific pressure through the pressure regulating valve. When the set pressure is reached, cut off the workpiece to be measured and the gas supply circuit, and keep the pressure stable for a specific time. During the pressure stabilization period, the instrument will give priority to determine whether the workpiece has large leakage according to the leakage situation. Then enter the detection phase. The pressure sensor records the current real-time pressure indication. After a period of detection, Read the real-time pressure indication again and compare it with the previously recorded pressure indication. If the measured workpiece leaks, the difference between the two pressures is the pressure drop of the workpiece during the detection cycle. The larger the value, the more serious the workpiece leakage. If the difference is within the allowable range, the tested workpiece is considered as qualified. Otherwise, it is unqualified.

2、 Differential pressure method

The differential pressure air tightness detection method, also known as comparison method, is applicable to common air tightness tests such as IP waterproof test, including: automobile and motorcycle oxygen sensor, fuel pump, gearbox, motor, harness, battery pack, controller (VCU), engine assembly, cylinder block, cylinder head, air inlet manifold, radiator, reversing radar, mobile phone accessories, bracelet accessories, watch accessories, tuner, die-casting aluminum parts, valve pipe fittings, etc.

The differential pressure method test is to add a differential pressure sensor on the basis of the direct pressure test, which is characterized by small range and high resolution. It is mainly applied to the test of some workpieces with high sealing test accuracy.

During inflation, all valve groups are opened, and the pressure at both ends of the differential pressure sensor is the same. At the beginning of pressure stabilization, the valve group is closed, and the pressure tends to be stable from fluctuation. The pressure at the standard part end of the differential pressure sensor remains unchanged, and the other end is connected to the test workpiece. When there is leakage at the test end, the pressure at the test end drops. The differential pressure sensor compares the pressure at both ends to calculate the small leakage.

3、 Closed chamber method

The closed volume method, also known as quantitative method and volumetric method, is applicable to the testing of workpieces without air filling holes, such as bracelets, cameras, mobile phones, watches, car lights, outdoor lights, Bluetooth headphones, tire pressure sensors, electric toothbrushes, flashlights, stage lights, walkie talkies, etc.

Test method: put the workpiece to be inspected into a sealed chamber. After starting the test, the leak detection system will open the gas circuit switching valve 1 and switching valve 3 to inflate the gas metering device. When the air pressure reaches a specific amount, the gas circuit switching valve 1 and switching valve 3 will be closed, and the gas circuit switching valve 4 will be opened, and the gas of the gas metering device will be released into the test chamber. If there is a big leak in the workpiece, the pressure will drop quickly. If it exceeds the low limit value set by us, the system will give an alarm. If the workpiece has micro leakage, the pressure will drop slowly and can be detected by a high-precision leak detector.

4、 Flow method

It is applicable to IP65 waterproof test and workpiece flowability test, such as: infusion tube, capillary copper tube, horn, waterproof breathable film, etc.

It is required that the pressure of the air inlet source shall exceed the test pressure by more than 1 bar. After the pressure is adjusted through the pressure regulating valve, the gas enters the test workpiece through the flow sensor; The direct pressure sensor monitors and tests whether the internal pressure of the workpiece can meet the requirements in real time. If the requirements are met, the value of the gas passing through the flow sensor is the flow of the workpiece under the pressure.

5、 Mass flow method

It is applicable to gearbox housing assembly, battery pack, controller (VCU), automobile radiator, automobile motor and other workpieces with large volume and small leakage, and can also reduce the impact of temperature and other environmental factors on the test.

Test method. The leakage amount of the whole system is calculated through the formula.

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