Problem description:The same product with the same parameters yields different test results on different machines.
Cause analysis:Air tightness test results are variable and are affected by factors such as product deformation, temperature, product volume, and fixture sealing. Therefore, it is normal for the same product tested with the same parameters to produce different results.
Convert pressure decay into leak rate through a standard leak orifice. Simply put, the pressure decay value PA of each tester is calibrated to 0 sccm, thereby unifying the test differences among different machines.
Problem description:Why can't an air tightness tester be set to "zero leakage"?
Answer:An air tightness tester is used to measure leak rates, but no product in the world is completely leak-free—so-called "zero leakage" is always relative. The air tightness tester monitors test data through a pressure sensor. Even if the product does not leak, the following factors can still cause data fluctuations:
Therefore, the leak standard will not be absolute zero.
Problem description:The test result shows a negative value (such as -2 Pa, -5 Pa, etc.).
Answer:It depends on the test principle:
Problem description:Imported brand leak detector displays a negative value.
Cause analysis:The differential pressure method is a comparative test and has a reference port. A negative value means the "reference port" has a larger leakage value than the "test port."
Problem description:Leak value displays 9.999 (or a similar full-scale value).
Answer:A common scenario is the use ofCOSMO 1866 Series Leak Detector. Displaying this data indicates:
Problem description:What are gross leaks, fine leaks, large leaks, and micro leaks? What are the standards?
Answer:There is no unified standard for what constitutes a coarse leak, fine leak, large leak, or micro leak. Different products and different pressures naturally produce different results.
Experience reference (100 kPa pressure, 10s test):
| Pressure decay range | Determination |
|---|---|
| ≤ 50 Pa | ✅ Pass |
| 50~100 Pa | ⚠️ Micro leak |
| > 100 Pa | ❌ Major leak |
Problem description:At the instant the inflation ends and the switch is made to the stabilization stage, the pressure suddenly drops.
Reason:
Answer:Check whether the corresponding test pressure is reached at the end of inflation:
Problem description:The instrument shows that the pressure does not reach the set value.
Troubleshooting steps:
| No. | Inspection Items | Countermeasures |
|---|---|---|
| 1 | Is the product experiencing a major leak? | The pressure cannot build up, which may be caused by a large leak in the product. |
| 2 | Front-end air pressure | Confirm the pressure is between 0.4 and 0.6 MPa. |
| 3 | Air source too low or fluctuating | Ensure the air supply remains stable above 0.4 MPa; during testing, do not use pneumatic tools such as air guns on the air supply. |
| 4 | Check whether the test pressure regulating valve setting has changed. | Self-check: Pressure setting → Pressure regulation → Real-time pressure setpoint |
| 5 | Test fixture not sealed | Check whether the sealing fixture is in a sealed state. |
| 6 | Air pipe leakage | Check the test air hose and connectors. |
| 7 | Insufficient inflation time | Extend the inflation time |
| 8 | Insufficient volumetric inflation time | Extend the volume filling time |
| 9 | Pressure sensor failure | Contact the manufacturer for repair. |
Answer:Air tightness testers generally use differential pressure sensors or direct pressure sensors, so the measurements are naturally in pressure units (Pa, kPa, bar, MPa), collectively referred to asPressure decay valueOrLeak rate。
Some air tightness testers display sccm, scc, or cc/min, collectively referred to asLeak rate。
The pressure decay and flow rate are correlated and calculated using the air tightness test formula. The specific formula is as follows:
Among them:
Problem description:How do you determine the volume of an air tightness test system?
Answer:Different manufacturers use different methods, but all of them calculate based on the air tightness testing formula.
Then the volume V can be calculated.
| No. | Function |
|---|---|
| 1 | Verify the sensitivity of the air tightness tester |
| 2 | As the confirmation standard for leak rate accuracy |
| 3 | Measure the pumping speed of the vacuum pump. |
| 4 | Calibrate vacuum gauges and other equipment |
When the test product is judged by sccm leak rate, a standard leak orifice is inserted during the test, and the leak orifice data is compared with the test data to verify the accuracy of the instrument.
Problem description:The air tightness leak detector is itself a machine and can also experience failures.
Common faults and countermeasures:
| No. | Fault | Cause | Countermeasures |
|---|---|---|---|
| 1 | Inaccurate test results | There is a problem with the instrument itself. | Consult the manufacturer and repair according to the service manual. |
| 2 | Instrument self-leakage | Internal structural damage | Find the leak point and repair it. |
| 3 | Pressure relief valve failure | Unable to control system pressure release, resulting in over-pressurization | Replace the damaged pressure relief valve |
| 4 | Sensor damage | Sensor failure, unable to detect correctly | Replace the damaged sensor |
| 5 | Pump damage | System pressure insufficient | Replace the damaged pump |
| 6 | Control system failure | Circuit and connection issues | Check the circuit, repair or replace faulty components. |
| 7 | Instrument wear | Component wear after prolonged use | Regularly inspect and replace worn parts. |
Answer:Each of the two methods has its own applicable scenarios:
| Test Methods | Principle | Accuracy | Applicable Scenarios |
|---|---|---|---|
| Direct pressure method | Inflate the product, shut off the air supply, and monitor the pressure decay value. | Medium | For larger-volume products, a certain amount of leakage is allowed. |
| Differential pressure method | The test piece and the standard piece are inflated simultaneously, and the pressure difference between them is compared. | High (temperature interference can be eliminated) | Precision products, micro-leak detection |
Based on industry experience, the causes of air tightness test failures can be systematically investigated from the following 10 dimensions:
| No. | Fault point | Instructions | Countermeasures |
|---|---|---|---|
| 1 | Ambient temperature fluctuation | Gas is sensitive to temperature; air conditioning airflow, personnel movement, and day-night temperature differences cause pressure fluctuations. | The testing area is isolated and temperature-controlled to protect the instruments from drafts. |
| 2 | Product microscopic defects | Welding micro-cracks, casting blowholes, and temporary blockages from dust that come loose, causing intermittent good-and-bad results. | Trace production processes and strengthen incoming material inspection. |
| 3 | Test line issue | The pipeline is too long or too thin, causing high resistance; tubing that is too hard or too soft affects pressure fluctuation. | Select tubing with a smooth inner wall and appropriate hardness. |
| 4 | Insufficient fixture accuracy | Aging and worn sealing rings, or fixture deformation, can generate "false leak" signals. | Regularly inspect and replace seals. |
| 5 | The instrument itself is not in good condition. | Sensor drift, blocked or leaking air lines, failure to calibrate regularly | Calibrate regularly using standard parts. |
| 6 | Unreasonable test parameter settings | Improper inflation/balance/test time, leak threshold too strict or too loose | Verify and optimize parameters based on product characteristics |
| 7 | Non-standard operating procedures | Product not properly clamped, connector not tightened, equipment status not confirmed | Establish SOPs and enforce them strictly. |
| 8 | Product internal volume change | Liquid accidentally injected into the cavity causes a change in volume, resulting in an abnormal negative value. | Troubleshoot medium residue in the production process |
| 9 | Electromagnetic interference | Interference from the startup and shutdown of large on-site equipment affects sensor signals. | Add shielding and vibration damping devices |
| 10 | System Solution Design Defects | Improper selection of standard products, and mismatch between the test method (direct pressure/differential pressure) and the product. | Re-evaluate the test plan |
Systematic troubleshooting steps:
Theoretical basis:According to the ideal gas law equationpV = nRT
Problem description:During differential pressure testing, the test part seals better than the reference part, resulting in a negative value.
Cause analysis:Before an air tightness tester displays the leak rate (sccm / cc/min), it needs to performCompensation and Calibration：
If the product actually has better sealing performance than the standard part, a negative value will appear—in this case, it is necessary toRecalibrate the system zero point。
Theoretical ambient temperature requirement:5–40°C, relative humidity not exceeding 85%.
Practical experience:
Troubleshooting method (process of elimination):
Problem description:Qualified products are frequently falsely reported as leaking, resulting in a high false rejection rate.
Root causes and countermeasures:
| Cause | Countermeasures |
|---|---|
| Sensor zero drift, temperature drift, and failure to calibrate regularly | Perform zero calibration and span calibration, and calibrate with a standard part. |
| Large temperature fluctuations in the workshop cause a noticeable temperature difference between the product and the fixture. | The testing area is kept at a constant temperature, and the product is allowed to stabilize at that temperature before testing. |
| Slight internal leakage of solenoid valves and check valves | Replace the micro-leak valve assembly and perform air tightness verification. |
| Holding time too short, leak threshold set too strict | Reasonably extend the test time and relax the threshold within a reasonable range. |
| Aging of fixture sealing gaskets, deformation of fixtures under load | Replace the sealing gasket, and correct the fixture parallelism and clamping force. |
Problem description:Defective products with leaks are judged as qualified, and defective products flow into the next stage.
Root causes and countermeasures:
| Cause | Countermeasures |
|---|---|
| Sensor sensitivity degradation, aging and moisture exposure | Calibrate with a standard leak orifice; replace if sensitivity is insufficient. |
| Leak allowance set too high | Recalibrate the standard leak orifice and narrow the judgment threshold. |
| Insufficient inflation time; pressure not stabilized. | Extend the pressure stabilization time to ensure the pressure is stable before testing. |
| Product positioning offset, sealing surface not fully covered | Reposition the fixture and replace the seals. |
| Air circuit orifice or filter element clogged | Fully disassemble the air circuit and clean oil, dirt, and debris. |
| Software parameters lost, wrong test mode selected | Restore factory parameters and reconfigure. |
Answer:Replace immediately if any of the following occurs:
Maintenance recommendations:It is recommended to wipe the sealing ring surface with a lint-free cloth before the start of each shift, check the condition of the sealing ring once a week, and replace the wearing sealing parts once a month.
| Sampling accuracy | 24bit |
| Differential pressure sensor range | ±500 / ±1000 / ±5000 Pa |
| Parameter group | 99 sets |
| IO interface | 8 IN / 8 OUT |
| Data interface | RS232、TCP/IP |
| Display | 5-inch color touchscreen |
| Power supply | 220 VAC / 50 W |
| Air supply pressure | 0.4~0.6 MPa |
| Operating temperature | 0~50°C |
| Volume | 250×300×160 mm |
| Weight | 2.5 kg |
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