A vacuum leak detector is a key equipment used to test the sealing performance of vacuum systems or containers. Its detection method is mainly based on the physical characteristics of gas leakage in a vacuum environment, by measuring pressure changes, gas composition, or flow characteristics to locate the leakage point. The following are common detection methods, their principles, steps, and application scenarios:
1、 Pressure drop method (direct pressure method)
Principle:
After pumping the inspected item to a vacuum state, turn off the vacuum pump and monitor the pressure changes in the system over time. If the pressure rises, it indicates the presence of a leak.
Steps:
Connect the inspected item to the vacuum leak detector and evacuate it to the set pressure (such as 10 ⁻ ³ Pa).
Close the vacuum pump and valve, and isolate the inspected item.
Record the pressure variation curve over time and calculate the leakage rate (such as Pa · L/s).
Features:
Advantages: Easy to operate, suitable for rapid screening of large leaks.
Disadvantages: Low sensitivity, difficult to detect small leaks (such as<10 ⁻⁶ Pa · L/s).
Application: Rough inspection of industrial pipelines, large containers, vacuum furnaces, etc.
2、 Helium mass spectrometry leak detection method (high-sensitivity detection)
Principle:
Using helium as a tracer gas, the helium concentration at the leak site is detected by a mass spectrometer. Helium molecules are small, highly penetrable, and can be detected by mass spectrometers at extremely low concentrations (up to 10 ⁻¹² Pa · m ³/s).
Steps:
Spray gun method (suction gun mode):
Vacuum the inspected item to a high vacuum state.
Spray helium gas onto the suspected leak point with a spray gun, and the mass spectrometer detects the helium signal through a suction gun.
真空箱法：
Place the inspected item into a vacuum chamber filled with helium gas, and after vacuuming, detect the change in helium concentration inside the chamber using a mass spectrometer.
Features:
Advantages: High sensitivity, able to locate small leakage points.
Disadvantages: High equipment cost, requiring professional operation.
Application: High precision fields such as semiconductors, aerospace, nuclear industry, etc.
3、 Halogen leak detection method (alternative to Freon)
Principle:
Using halogen gases (such as R12, R22) as tracers, the gas concentration at the leak site is detected by a halogen detector (such as an electronic halogen leak detector).
Steps:
Fill the inspected item with pressurized halogen gas.
Scan the surface with a detector probe and observe changes in readings.
Features:
Advantages: Low cost, suitable for low to medium sensitivity detection.
Disadvantages: Halogen gases may damage the ozone layer (requiring environmentally friendly alternatives) and have lower sensitivity than helium mass spectrometry.
Applications: refrigeration systems, automotive air conditioning, etc.
4、 Ultrasonic leak detection method (non-invasive testing)
Principle:
The gas turbulence generated by leakage will emit ultrasonic waves (above 20kHz), which are captured by ultrasonic sensors to locate the leakage point.
Steps:
Scan the ultrasonic probe on the surface of the inspected item.
Determine the leakage location based on signal strength and frequency changes.
Features:
Advantages: No need for vacuuming or inflation, suitable for pressurized systems; Can detect liquid leaks.
Disadvantage: Environmental noise may interfere with the detection results.
Application: Rapid on-site inspection of pipelines, valves, pressure vessels, etc.
5、 Fluorescence leak detection method (visual detection)
Principle:
Inject fluorescent dye into the tested system, and the leaked dye will seep out and emit light under ultraviolet radiation, which can be observed and located through a camera or the naked eye.
Steps:
Inject fluorescent dye into the system.
Run the system to circulate the dye.
Illuminate with ultraviolet light and observe the luminous point.
Features:
Advantages: Intuitive visualization, suitable for complex systems.
Disadvantage: The system needs to be cleaned to remove residual dyes.
Applications: automotive air conditioning, hydraulic systems, etc.
6、 Differential pressure method (comparative testing)
Principle:
Vacuum two identical containers (one with a known seal and one to be inspected) simultaneously and compare the pressure changes between the two. If the pressure of the container to be inspected rises faster, there may be a leak.
Steps:
Connect the test piece and the standard piece in parallel to the vacuum system.
After vacuuming, isolate and monitor the pressure difference between the two.
Features:
Advantages: Eliminate environmental interference and improve accuracy.
Disadvantages: Standard parts are required and the operation is more complex.
Application: Quality inspection in mass production.
7、 Accumulated leak detection method (long-term monitoring)
Principle:
Long term monitoring of pressure or gas concentration changes within the inspected item, and calculation of total leakage through integration.
Steps:
Isolate the inspected item after vacuuming.
Continuously record pressure or gas concentration data.
Analyze data to calculate leakage rate.
Features:
Advantages: Suitable for long-term monitoring of extremely small leaks.
Disadvantages: Long detection cycle and low efficiency.
Application: High vacuum system, spacecraft sealing testing.
8、 Laser interferometry (high-precision optical detection)
Principle:
Use a laser interferometer to detect the change in gas refractive index caused by leakage, and calculate the leakage location through the optical path difference.
Steps:
Launch a laser beam towards the inspected area.
Analyze the changes in interference fringes of reflected or transmitted light.
Features:
Advantages: Non contact, high precision (up to micrometer level).
Disadvantages: Expensive equipment and complex operation.
Application: Semiconductor chip packaging, optical component testing.
Summary: Method selection criteria
Sensitivity requirements: Helium mass spectrometry (highest)>Halogen method>Pressure drop method.
Detection speed: Ultrasonic and fluorescence methods are faster; Helium mass spectrometry is slow but accurate.
Cost limitations: Pressure drop method and ultrasonic method have low costs; Helium mass spectrometry and laser methods have high costs.
System status: The pressurized system is suitable for ultrasonic method; The vacuum system is suitable for helium mass spectrometry.
Based on specific scenarios (such as industrial production, scientific research experiments, on-site maintenance) and leakage rate requirements (such as 10 ⁻³ Pa · L/s or 10 ⁻¹² Pa · m ³/s), choose the most suitable method or combine multiple methods to improve reliability.