The core working principle of an air tightness tester is to apply a stable medium pressure to the test piece, collect pressure or differential pressure change data during the pressure holding stage, calculate the leakage rate, and determine whether the sealing performance is acceptable. The two mainstream methods are differential pressure testing and direct pressure testing.
1. Main Principle Types and Applicable Scenarios
Differential Pressure Method (accounting for more than 80% of industrial applications)
Principle: A fixed amount of dry compressed air is simultaneously charged into the test piece and a standard reference part of the same specification that is known to be absolutely sealed. After the air supply is closed, a high-precision differential pressure sensor measures the pressure difference between the two. If the test piece leaks, its pressure drops over time, and when the differential value exceeds the preset threshold, the part is judged as leaking and unqualified.
Applicable scenarios: Small precision components such as sensor housings and electronic connectors, as well as workpieces with low leakage requirements.
Direct Pressure Method
Principle: Gas is charged directly into the test piece to a preset pressure. After the pressure holding stage, a high-precision pressure sensor measures the pressure decay rate of the test piece. If the decay rate exceeds the set value, the part is judged as leaking.
Applicable scenarios: Large-volume, low-pressure workpieces such as automobile tires, fuel tanks, pipes, and tube fittings.
2. Core Testing Process
Sealing the test piece: All openings of the test piece are sealed with custom fixtures, leaving only the connection channel to the tester to ensure there are no additional leakage paths. For these custom sealing fixtures and adapter components, Hansheng Automation provides precision machining services based on customer drawings and required tolerances to support stable and repeatable test setups.
Inflation and pressure stabilization: Gas is charged according to set parameters. The medium is usually dry, oil-free compressed air, with a pressure range of 0.02–1.0 MPa adjusted according to workpiece pressure resistance. The system waits until the pressure stabilizes to eliminate interference from temperature changes and workpiece deformation during inflation.
Pressure holding and detection: The system enters the pressure holding stage. Sensors continuously collect pressure data and calculate the leakage rate, typically expressed in Pa·m³/s or mL/min.
Judgment output: The measured leakage is compared with the preset threshold, and a pass or fail signal is output.
3. Professional Application Boundary Requirements
Medium compatibility: Flammable or explosive workpieces require inert gas such as nitrogen to avoid safety risks caused by high-pressure air.
Parameter matching: Pressure thresholds and holding time must be set according to workpiece material and wall thickness to avoid overpressure damage.
Environmental requirements: Testing should be performed in a constant temperature environment of 20±5°C, because temperature fluctuations can affect pressure data accuracy.
