Air/Gas Leak Testing Techniques

Water Immersion / Soap Solution

Pressurize part under water and look for air bubbles or spray outside of part with soap/water solution and look for bubbles caused by air leakage out of the part.

Advantages

  • Can be fast for larger leaks on small parts when testing multiple at one time.
  • Can be fast for testing extremely large parts with larger leaks; few areas for possible leak.
  • Best method for detecting exact leak location detection.
  • Low equipment cost.

Disadvantages

  • Risky: An extremely operator dependent technique with a high possibility of passing actual failures.
  • Slow: Detecting small bubbles on typical parts can take much longer than other methods.
  • Added cost: Parts must typically be dry and free of fluid before shipping.
  • Less sensitive than other techniques on most parts.
  • No leak rate or test result information.

High Frequency Sound

Pressurize part and use hand held "listening" device around potential leak areas and watch for high pitched noise caused by leakage of air out of the part.

Advantages

  • Good for detecting leak location.
  • Low Equipment cost.

Disadvantages

  • Background noise can reduce sensitivity of the device.
  • Can be very slow for finding small leaks.
  • No leak rate or test result information.
  • Cannot test internal cavities.

Trace Gas Detection (Mass Spectrometer)

Pressurize part with Trace Gas such as Helium or Argon inside a high-vacuum chamber and detect the quantity of trace gas caused by leakage out of the part using an electronic Mass Spectrometer sensor. Can be hand held "sniffer" as well.

Advantages

  • Outstanding sensitivity. Best solution for leak rates below .1 cc/min

Disadvantages

  • Very expensive: Equipment investment typically starts at or above $100K. Fixturing usually elaborate.
  • Expensive to operate: Trace gas consumed is often high.
  • Slow: Typically, the part is placed into a chamber and closed off. A hard vacuum must be pulled on that volume before the actual test can take place.

Mass Flow

Pressurize part and measure air flow caused by leakage out of the part using electronic mass flow sensors.

Advantages

  • Very fast for large leak rates (over 100 cc/min).
  • Works best for checking size of fluid/air path or detecting restrictions in part channels.
  • Non-Operator dependent and test data can be obtained.

Disadvantages

  • Sensitivity too low for leak rates below 100 cc/min.
  • Accuracy of readings very dependant upon air temperature and actual system pressure.
  • More costly than pressure decay testing as it requires both a mass flow and a typical pressure decay transducer for each test channel.

Pressure/Vacuum Decay

Pressurize or apply Vacuum to the part and measure pressure/vacuum change within the part caused by leakage using electronic pressure-decay sensors.

Advantages

  • Fastest, most consistent test technique for 90+% of welded plastic components.
  • Non-Operator Dependent and test data can be obtained.
  • Accurate on leak rates as low as .1 cc/min.
  • No cleaning/drying operations required after testing.
  • System accuracy immune to most environmental conditions.
  • Can be configured for 100% testing downstream of most bonding operations.

Disadvantages

  • Not usable for leak location.
  • More costly than immersion testing.
  • Slow with large part volumes and small leak rates.