Leakage flow is a micro-flow measurement application, designed to identify small capillary paths or pinholes that effect product sealing integrity. The Intelligent Gas Leak Sensor (IGLS) is a micro-flow sensor designed for leak test applications. The leak flow measurement itself is not dependent on the test volume, ambient temp. etc., and is a stable and highly repeatable measurement.
Leak flow is not a simple viscous gas or liquid flow, and in many cases slip or molecular flow, and analytical flow calculations are not straightforward.
ATC, Inc. offers various devices to help you meet your leak testing requirements. Analyzing your application is critical in order to optimize your solution. The following steps should be taken:
Define your leak tightness. Answer the simple question: “What is the single, smallest capillary path or pinhole that is acceptable for my application?” Define your equivalent channel (EC) or equivalent diameter (ED). This will result in defining your maximum allowed flow rate at the pressure (or vacuum) condition selected. If you need help defining your leak tightness contact ATC, Inc. for more information.
Calculate your H number, which is:
§ H – Difficulty level, a dimensionless number, indicative of system response to flow development time.
§ q – Specified leak rate in cc/min (note: volumetric leak flow rate in actual cc/min).
§ V – Test volume, in cc. Test volume is Unit Under Test (UUT) and connecting tubes volume.
§ t – Measurement time, which includes desired measurement time, in sec. The time allowed for flow stability and testing, during which a repeatable flow can be measured.
Note: Total cycle time = Total fill time + Measurement time. Fill time is the time required for part charging/filling/evacuating time (from 20% to 100% of test time). UUT load/unload and seal time are not included.
Very high H number (typically more than 5,000) indicates that the leak flow will develop slower than the desired test time, due to the ratio of specified leak rate and test volume. Low H number, indicates that system natural response time to develop the specified leak rate is within the desired test time.
Very high H number may require various options, such as an active pressure to be added to the system, or using multiple test systems for a given production rate. For these cases, consult ATC, Inc.
Define your IGLS leak flow and pressure range. Use the Leak Flow Simulator or IGLS spec sheet. It is recommended that your specified leak rate will be 10-30% of its full range, especially in cases where short cycle time is required. If you have questions, please reference the FAQ page or contact us directly.
Check the UUT for hidden cavities or “virtual leaks.” Hidden cavities will cause air to leak into them, when pressurizing the UUT, or act as a gas reservoir, when testing under vacuum. The lower the leak rate, or the higher the H number, the more sensitive the application becomes to virtual leaks. Consult ATC, Inc. to add features in your system to reduce this effect.
Select connection types and tubing sizes. When using an automated fixture for low leak rates the fixture seal design is critical. Fixture and tubing “dead volume” should be kept to a minimum. Consult ATC, Inc. or refer to ATC’s application notes for recommended connections.
Your leak test system should include an Equivalent Channel (or Equivalent Diameter) to be used as a “Verification Orifice.”