Three common leak detection methods for helium leak detector

Helium leak detectors are widely used. According to the sealing requirements of different products, negative pressure method, positive pressure method and helium pressure method are used.

1.Leak detection for negative pressure method

Negative pressure method leak detection is to connect the detection component to the detection port of the leak detector, and use a spray gun to continuously spray tracer gas into the suspected leak hole. The tracer gas enters the leak detector through the leak hole and is detected. General electronic equipment shells, high-voltage switch tubes, zinc oxide, lightning arresters, etc. should use this method for leak detection.

Depending on the product, different sizes of clamps or auxiliary tools need to be selected. For example, leak detection of tube shells. After the leak detector works normally, the leak rate can be calibrated with the standard leak hole, and the tube shell can be sprayed for leak detection. First, the clamp is fixed on the leak detection port, and the tube shell to be tested is placed on the rubber plate above the clamp. The auxiliary air extraction system pumps it into a predetermined vacuum, and then automatically connects to the measurement system of the instrument. Then use a spray gun to continuously spray helium gas into the tube shell, usually taking 1 to 3 seconds. When there is a leak in the tube shell, helium will enter the mass spectrometry analysis part of the instrument through the leak hole, and the size of the leak will be directly displayed on the leak rate table. This method can not only determine the location of the leak hole, but also measure the size of the leak hole. The entire test cycle takes just one minute.

2.Leak detection by positive pressure method

Leak detection using the positive pressure method is the opposite of leak detection using the negative pressure method. The sniffer gun is connected to the detection port of the leak detector. The detection device is filled with tracer gas at a specified pressure. The helium leaked from the leak hole is sucked into the leak detector for detection. It is very uneconomical to perform negative pressure leak detection on large containers or internal exhaust pipe containers, and the leak detection speed is slow. Positive pressure leak detection is generally used.

This positive pressure leak detection method should be noted: first, the sniffer sensitivity of the instrument must be calibrated, and then the container must be filled with helium with a higher pressure than atmospheric pressure; second, some containers have a thin plate structure. It is recommended to make a clamp outside the container to prevent high-pressure deformation and damage to the equipment; when the third suction gun moves along the weld, the speed should not be too fast and should be about 1mm away from the surface to ensure suction sensitivity. It is best to make the probe into a bell mouth shape.

3.Leak detection by helium pressure method

Leak detection by helium pressure method is to put the detection piece of tracer gas with a certain pressure into the leak detection fixture, and then connect it to the leak detector for emptying. The tracer gas leaks through the leak hole, and the leak detector detects the total leakage amount.

Generally speaking, this leak detection method should be used for small electronic equipment. First adjust the instrument, then place the device into a pressurized tank and press in helium. Helium enters the leaky device, and the device without the leak only absorbs the helium on the surface. The pressure and time of the equipment depend on GB2423, 2328 documents. After being removed from the pressurized tank, the helium absorbed from the surface is blown out and then placed in a leak detection fixture to evacuate. After the vacuum pump reaches the set value, the fixture will automatically connect to the instrument’s measurement system. At this time, helium leakage in the leakage device is detected, and the leakage rate is displayed on the leakage rate meter.

Helium pressure leak detection generally uses the elimination method. Place a certain number of devices in the fixture. The total leakage rate of this batch does not exceed the scrapped predetermined value, indicating that the batch is qualified; if the total leakage rate exceeds the scrapped predetermined value, half can be taken out, and the remaining half will continue to be checked for leakage. If this half is qualified, it means that the leaking device is in the half of the device that is taken out to check for leaks until the leaking device is detected.