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What are the leak test methods?

by:Rika Sensors     2021-11-26


Air tightness tester, also known as tightness tester, leak detector, leak detector, is an advanced non-destructive testing method, through inflating the product (compressed air or nitrogen), stabilizing, testing, and then The leak detection system obtains its pressure drop (pressure decay) value, leakage rate, etc. according to a series of analysis samples and calculations, so as to make a judgment on the product. At present, the most common test methods (specifically Wanken leak detection system) include direct pressure method (absolute pressure method), differential pressure method, closed volume method (quantitative method, volume method), flow method and mass flow method.







1. Direct pressure method







The direct pressure method is also called the absolute pressure method, which is suitable for the test of parts that require low precision or low pressure in the sealing test, and the IP65 waterproof test.







Leak detection principle: Fill the inner cavity of the tested workpiece with a certain pressure of gas (compressed air or nitrogen) through the pressure regulating valve. After reaching the set pressure, cut off the tested workpiece and the gas source gas path for a certain period of time Make its pressure tend to stabilize. During the stabilization period, the instrument will prioritize whether there is a large leak in the workpiece according to the leakage situation, and then enter the detection stage. The pressure sensor records the current real-time pressure indication. After a period of detection, the real-time pressure indication is read again and Comparing with the previously recorded pressure indication, if the measured workpiece has a leak, 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 leakage of the workpiece. If the difference is within the allowable range, the tested workpiece is considered qualified. Otherwise, it is unqualified.







Two, differential pressure method







The differential pressure air tightness test method is also called the comparison method, which is suitable for common air tightness tests such as IP waterproof test, including: fuel pump, gearbox, motor, wiring harness, battery pack, controller (VCU), engine head Into, cylinder block, cylinder head, intake manifold, radiator, reversing radar, mobile phone accessories, bracelet accessories, watch accessories, tuner, die-cast aluminum parts, valve pipe fittings, etc.







The differential pressure method test is based on the direct pressure test, adding a differential pressure sensor. It is characterized by a small range and high resolution. It is mainly used in the test of some parts with high sealing test accuracy.







When inflating, all valve groups in the figure below are all opened, and the pressure at both ends of the differential pressure sensor is the same. When the voltage stabilization starts, the valve group is closed, the pressure tends to stabilize from fluctuation, and the pressure at the standard part of the differential pressure sensor remains unchanged. One end is connected to the test workpiece, and when there is a leak at the test end, the pressure on the test end drops. The differential pressure sensor compares the pressure at both ends to calculate a small leak.







3. Closed cavity method







The closed volume method is also called the quantitative method and the volume method. It is suitable for bracelets, cameras, mobile phones, watches, car lights, outdoor lights, Bluetooth headsets, tire pressure sensors, electric toothbrushes, flashlights, stage lights, walkie-talkies, etc. Workpiece testing of gas-filled holes.







The test method is to put the workpiece to be inspected into a sealed cavity. After the test is started, the Wanken leak detection system opens the gas circuit switch valve 1 and the switch valve 3, and inflates the gas metering device to reach a certain amount After air pressure, the gas circuit switch valve 1 and the switch valve 3 are closed, and the gas circuit switch valve 4 is opened, and the gas of the quantitative gas device will be released into the test chamber. If the workpiece has a big leak, the pressure will drop quickly, and if it exceeds the low limit we set, the system will alarm. If the workpiece has a slight leak, the pressure will slowly drop, which can be detected by the Wanken high-precision leak detector.







Fourth, the flow method







It is suitable for IP65 waterproof test and workpiece circulation test, such as: infusion tube, capillary copper tube, horn, waterproof and breathable membrane, etc.







The test requires that the air inlet pressure must exceed the test pressure by more than 1 bar. After the pressure is adjusted by the pressure regulator, the gas enters the test workpiece through the flow sensor; the direct pressure sensor monitors in real time whether the internal pressure of the test workpiece can meet the requirements, and if it meets the requirements , The value of the gas passing through the flow sensor is the flow rate of the workpiece under the pressure.







5. Mass flow method







Suitable for large and small leaking parts such as gearbox housing assembly, battery pack, controller (VCU), car radiator, car motor, etc. It can also reduce the impact of environmental factors such as temperature on the test.







The test method is to inflate the gas storage tank first when inflating. After reaching a certain pressure, cut off the gas supply pipeline, close the intake valve, open the on-off valve of the workpiece to be tested, and start the test after it is stable. If there is a leak at the test end, the gas in the test chamber will flow to the test end. At this time, a mass flow meter can be used to detect the leakage rate from the gas storage end to the test end. Calculate the leakage of the entire system through the formula.


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