In a basic example of tracer gas leak testing, a tracer gas is introduced to one side of the test subject. Then a differential pressure is applied to the test subject, with the higher pressure at the tracer gas side. An instrument, such as a mass spectrometer, is then applied to the lower-pressure side of the test subject to detect the presence of the tracer gas. The gases used in this method are typically helium, hydrogen and refrigerant halides (R-12, R-22).
Tracer gas leak testing is performed in many industries, including automotive, beverage and medical device. Tracer gas leak testing is the most effective leak testing method, with the use of a mass spectrometer and the radioisotope method having the highest leak test sensitivity. Leak sensing times can be short, often ranging from 1 to 8 seconds, and test time does not usually increase greatly with part volume. With this method, testing can be automated, and tests can be performed at various temperatures. However, while some gases used in this method are inexpensive, the equipment is more expensive than that of other leak testing methods; furthermore, it will require calibration and usually special cleaning. There are safety issues as well. While gases such as helium do not pose health risks, some gases are hazardous, and concerns such as toxicity, radioactivity or flammability must be addressed.
Bubble emission leak testing has two basic techniques: immersion leak testing and film solution leak testing. In immersion leak testing, an internally pressurized test subject is immersed in a test medium. The subject stays in the test medium for a period of time and is then examined for bubbles.
In film solution leak testing, an internally pressurized test subject is covered with a liquid film solution that allows the formation of visually discernable bubbles. Bubble emission leak testing can be used with test subjects such as hydraulic and pneumatic tanks, tubing and pipe assemblies, and valves and valve seats. The method should be used when operator subjectivity can be tolerated and when allowable leakage can be large. While the technique is easy to learn and perform and is inexpensive, it is not quantitative and has limited leak-detecting sensitivity. Furthermore, it is time consuming and brings with it some safety concerns, such as water contamination and the risk of electric shock or fire.
Air leak testing manually or automatically applies regulated air pressure or vacuum to the test subject. Leakage is detected by loss of pressure or vacuum (pressure/vacuum decay) or the need to add air to compensate for air escaping from the subject. A range of devices can be used to detect pressure loss, from simple pressure gages and pressure switches, to complex electronic pressure transducers that report small pressure changes to electronic instrumentation. Likewise, a range of devices can be used for detecting flow, from simple water manometers or variable area flowmeters, to complex electronic transducers that report small flow changes to electronic instrumentation.
Air leak testing is used in the automotive and other industries for testing parts that will operate in service with liquid, gas or vacuum. Typically, air leak testing is fast, repeatable and no postcleaning is necessary. However, the method does not provide leak location and has low sensitivity. There also are safety issues involved when used at high pressures.
What follows are a number of leak test offerings for today’s nondestructive testing applications.
Pfeiffer Vacuum (www.pfeiffer-vacuum.com) introduces SmartTest, a portable helium leak detector. The instrument is designed with an operator-selected backing pump to match any application and comes with vacuum and sniffer standard operating modes. The instrument detects a leak rate for helium of 5 to 10-12 mbar l/s and an inlet pressure of 25 mbar. Combined, these enable an operator to begin testing soon after startup, and enable the operator to find very small leaks. It is designed with an integrated test leak for self-calibration and an optional industrial-proof handheld remote control.
The instrument is appropriate for quality helium leak detection requirements in a range of applications including semiconductor, automotive component testing, refrigeration, and air-conditioning assemblies and subassemblies.
Ulvac Technologies Inc. (www.ulvac.com) manufactures custom systems for automatic leak testing in automotive, refrigeration, air-conditioning and other industrial production lines. Based on the Heliot 700 leak detector, and employing Ulvac pumps, valves and gages, these ALT systems are modular in design with most of the major components being manufactured by Ulvac. This modular approach enables customization of the system to individual requirements, while maintaining as many standard components as possible.
Air-to-air cycling of the custom systems is automatic; components are placed in a vacuum chamber, charged with helium and the chamber is evacuated. A mass spectrometer-based helium leak detector is used to measure a total leak rate for the components to check all leak points to guarantee product quality. Pump systems are sized to evacuate both chamber and test part to a suitable pressure within a short period of time to meet the requirements of a desired machine cycle time. The leak detector used is the Heliot 700 with sensitivity to detect helium leaks as small as 1 x 10E-12 mbar-liters/second. The factory automation interface with the system can be engineered and supplied by Ulvac as well. Each system is equipped with a modem link so that system software troubleshooting can be done remotely by a telephone to the Ulvac service center, useful in enabling remote assistance for faultfinding and completing software changes with minimal delays.
Interlaken Technology Corp. (www.InterlakenPressure.com) introduces a new line of production leak testing systems. There are many leak sensor technologies available, such as pressure decay, vacuum decay and mass flow. The company integrates the appropriate sensor technology into a customer’s existing production lines and can incorporate such capabilities as data collection and analysis, and part marking and material handling. The company’s control module can communicate with other shop floor control systems via Ethernet, ProfiBus or CanBus.
The leak testing systems can be used to test high-pressure components at their operational pressures up to 100,000 psi. This allows companies to find leaks on high-pressure components in-house.
Standard and custom system configurations are available for a variety of applications. Pressure control modules are available to handle measurements from vacuum to ultra high-pressure.
Testing reports include testing measurement data, graphs and statistics for QC/QA monitoring.
The integration of the company’s standard pressure generation and control modules allows cost-effective solutions for a variety of applications in various markets, such as automotive, aerospace and medical.
Cincinnati Test Systems Inc. (www.cincinnati-test.com) introduces the Sentinel I-24. Test algorithms processed on a 32-bit system make the instrument a fast, repeatable and accurate leak detector. The instrument is multitest configurable for requirements such as pressure differential, sequential testing capability, pressure decay, vacuum decay, pressure gain and mass flow testing for flow capacity or leak rate. The instrument has automatic part setup for easy programming, and is compatible with USB, Ethernet and RS232 communication formats. The instrument’s auto calibration ensures accurate results and easy operation, while its environmental drift correction adapts to changing conditions, including temperature expanded I/O capability. Data storage is expandable through the USB port, and the instrument is available in benchtop or wall mount configurations.
Vacuum Instrument Corp. (VIC, www.vicleakdetection.com) introduces the Smart Charge III, the company’s third-generation evacuation and gas backfill system. The system is a fully automatic, configurable gas evacuation and backfill system with built-in gross-leak test used to pre-charge products under test with gas for leak detection, or for any gas charging application that requires evacuation and subsequent pressurization of the test product.
New features include an operator-selectable cumulative leak site integration feature to distinguish whether each individual leak site is an accept or a reject, and to determine if the accumulated leak measurements exceeds the specified leak reject limit; parts can either reject on one leak site or the accumulation of multiple sites. Other features include built-in gross leak test capability to eliminate tracer gas contamination; up to 10 part-specific recipes, each with up to 10 leak sites, with user configurable dwell time at each site; barcode scanner input; serial printer output; remote monitoring over an Ethernet connection; and PLC control allowing for flexible configuration.
The system can be integrated with the company’s MD-490S Real Sniffer portable dry industrial helium leak detector for tracer gas charging of products prior to fine leak testing. Gas recovery and mixing options also are offered to create a completely integrated gas handling and test system.
FasTest Inc. (www.fastestinc.com) introduces the ME001 connector for medical device leak test applications, used to test ultra-thin hypodermic and catheter tubing. The ME001 connects to diameters down to 0.015 inch, and is designed for leak testing infusion set and drug delivery devices. The compact 0.84-inch OD easily mounts in limited space locations and the pneumatic actuation is suitable for soft touch control of delicate components or automation for ergonomics or high-production testing.
Complementing the ME001 Series, the ME01 and ML001 connectors feature a maximum sealing capacity of 0.510 inch. Additional features include aluminum or stainless steel housings, FDA-approved seals and lubricant, and replaceable size and seal materials. The connectors are chemically cleaned and double bagged for added protection.
Uson L.P. (www.uson.com) introduces the Sprint iQ, a multifunction leak and flow tester that can test up to four parts simultaneously, using a range of test methods, high-resolution displays, advanced communication capabilities and intuitive logic. The instrument has a 24-bit analog to digital converter, which enables the accurate measurement of minute pressure and flow changes as low as 0.001 psig and flow ratings as low as 0.01 sccm.
The instrument is available with dual USB ports, RS232 serial port and optional Ethernet. It is compatible with the company's test reports and monitoring software. The device talks to a PLC and downloads the leak rate directly into a database to store device history records.
Programming and operation menus are intuitive, and information is displayed via the high-resolution color graphic interface, allowing clear viewing of pressure and flow curves as well as numeric data.
Varian (www.varianinc.com/vacuum) introduces its VS Series leak detectors, which have the simplicity of two-button operation combined with advanced system intelligence. The instruments have start and vent pushbuttons that permit simple day-to-day operation; navigation that allows easy access to system capabilities; programmable test sequences that minimize operator error and maximize production efficiency; and a high-definition touch-screen display that offers a range of languages and units of measurement for worldwide usage.
Available with the leak detectors is the Leak Test Data Wizard, a flexible, PC-based data management tool for use with the company's VS instruments. The software provides custom automation of leak test processes ensuring testing uniformity; step-by-step guidance through testing processes; and graphically displayed leak test results that provide individual part test histories or identify trends in high-volume test applications.
InterTech (www.intertechdevelopment.com) introduces the M1075-44z Micro Mass Flow Leak Detector, available with the company’s patented mass flow sensor. The instrument is designed for accurate downstream testing for leaks as small as 0.01 sccm. It provides an alternative to many helium mass spectrometer-testing applications. Features include patented bias leak technology that monitors test system integrity during the test cycle; leak range of 0.0100 to 0.2500 sccm; pressure range of 2 to 100 psig or 1 to 20 psig; transducer repeatability of 0.05% F.S.D; transducer sensitivity of 0.05% F.S.D; A/D conversion of 14 bit; 1,000 samples per second; timer increments of 0.01 second; and NIST-traceable calibration to less than 5% R&R.
ATC Inc. (www.atcinc.net) introduces the Model VE2, featuring the company’s patented micro-flow sensor, designed to meet increasing demands for a more versatile instrument with shorter cycle time, flexible controls and Ethernet connection, enabling remote viewing of system operation and data collection over a LAN. The instrument is used in vacuum applications from 1x10-5 sccs, using ATC’s patented Mass Extraction technology. The instrument has a touch screen with color graphical display. The instrument replaces many tracer gas applications, providing a direct measurement using air. Its long-term stability in variable ambient conditions provides operators with measurements that are repeatable and reliable. Optimal results are achieved when used for small to medium-sized parts.
Inficon (www.inficon.com) introduces the Protec P3000XL, a helium sniffer leak detector. The instrument can detect leaks from a considerable distance from the leak location and also on the backside of a tube joint, even while the sniffer tip is being moved. The instrument can be used for component and pre-assembly testing of refrigerators, freezers, automotive air-conditioners and similar products. Leak rates can be displayed in refrigerant-equivalent leak rates while taking into account the difference in fill pressure between helium and refrigerant charge. It also automatically adjusts the leak rate displayed as well as set trigger levels when using diluted helium.The unit can be operated via the probe display without access to the main unit. The built-in Pro-Check reference leak allows the operator to verify that the unit is functioning properly at the production line at any time. The operator-guiding mode, I-Guide, minimizes operator error by ensuring the correct number of locations (for example, the number of joints) on each unit under test is checked, and that each location is tested for the predetermined minimum time. Multiple alarm functions make sure alarms cannot be overlooked.