Leak Testing Fuel Injector Components

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A vehicle’s fuel injection system is responsible for injecting fuel into the engine cylinders, where the gas is burned to produce engine power. A leaky fuel injector, which is a common fuel injection system problem, can significantly compromise engine performance and produce a variety of symptoms.

As described in this article on eHow.com, small things like an erratic engine idle, a misfiring engine, reduced gas mileage and worst case, an excessive fuel leak onto the hot surfaces of the engine intake manifold or engine block causing the fuel to ignite and cause an engine fire. These problems can be arrested in the first instance with accredited testing systems.

Faulty fuel injector components not only are a threat to the end-user / consumer’s life, they also make terrible testimonials to your quality control. That we know isn’t the ideal situation for a component manufacturer, be it of any size.

InterTech’s leak testing solutions offer you unsurpassed excellence in testing solutions, both leak and functional. Here’s one such solution that has helped many manufacturers of fuel injector components to test and verify leaks in their manufactured components.

The Challenge

Fuel injection components often demand 100% leak testing to limits as low as .01 sccm with cycles as fast as 2.5 seconds, 10% R&R quality requirements, while also displaying significant part temperature variations.

Separate tests with different limits are typically needed in the same test cycle for body welds, seat leakage, and overall leakage. Integration of instrumentation software, fixturing and test circuit is essential, as is complete test documentation.

DR-109-Fuel-Injector-Components

Fuel Injector Test Fixture and Parts

Test Process and Solutions

InterTech’s downstream test process features a patented Micro-Flow mass-flow transducer to provide 10 times greater leak sensitivity than any other dry-air test method. A test part is enclosed within a test chamber and pressurized; leakage is measured as a flow increase into the test circuit outside the part, eliminating the need and time for pressure stabilization inside the part. The test circuit is precisely engineered for minimum volume, enabling the Micro-Flow sensor to almost instantaneously measure flows with a resolution of .0001 sccm.

Critical for fast small-leak testing, all fixtures and clamping devices are designed and built for absolute stability to prevent part movement during testing. Seal positioning mechanisms consistently address the test part squarely and firmly, stabilizing their closure forces quickly to shorten cycle times.

Seals are designed for high durability to run thousands of parts per day without replacement. With these unique features, Micro-Flow dry-air test systems deliver .01 sccm testing with less than 10% R&R.

Special Features

  • InterTech’s Patented Bias-Leak checking is especially important for fail-safe operation whenever testing to less than 1 sccm. It uses low-level airflow to confirm test-circuit integrity before each test cycle.
  • Temperature compensation sharpens test accuracy and repeatability by nullifying test part residual heat from welding, fabrication, washing or even operator handling. Custom algorithms based on the test part’s unique cooling characteristics supply appropriate corrective responses across the test cycle.
  • InterTech’s S-3085 networking/diagnostic software graphically visualizes for greater operator control the factors that can compromise a good baseline zero, trigger false rejects or otherwise disrupt accuracy and repeatability.

Follow the InterTech India blog for more solutions on leak and functional testing. For sales enquiries, you may contact us at;

Mobile: +91 994 032 0718

eMail: ajay@intertechdevelopment.com

Land phone: +91 44 4211 2525

 

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Leak testing 101 – Part 1

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Not too long ago, when you wanted a product to be leak-proof, you simply put it under water, made sure it didn’t bubble, and thereby concluded there were no leaks. Such “bubble testing” takes time and depends on the operator’s ability, making it totally inappropriate for the modern production environment. Also, it doesn’t generate the quantitative measurements that are the lifeblood of quality assurance engineering.

Dry-air leak testing methods—some of which can detect leaks as small as 0.01 standard cubic centimeters per minute (sccm)—are the methods most commonly used today by a wide range of industries—from medical devices, to automotive, to appliances, and aerospace, among others. These dry air methods enable quality managers to define leaks quantitatively.

“No leaks allowed” standards are concepts of the past. There are a variety of dry air leak test methods and best-practice techniques for each type of method, which will enable compliance to ISO 9001 and comparable quality management standards to be achieved. Generally speaking, these dry air leak test methods include;

  • Pressure testing
  • Differential pressure-decay testing
  • Mass flow leak testing

In addition, tracer gas testing and especially helium mass spectrometer leak testing, are used in more demanding applications where leaks as small as 10-5 standard cubic centimeters per second (sccs) must be detected in a production environment. If one truly understands leak testing application requirements and best practice techniques for these various leak test methods, the selection of which type of testing to perform is a rather straightforward matter.

The first step in designing a leak testing solution is to correctly define what the leak limits are. Leak testing applications laboratories begin with an engineering analyses of a specific application to determine and quantify how much a product or component can leak. Often, correlation studies are performed to verify if it is possible to use dry-air test methods instead of hydraulic fluids. Sample parts are tested as part of an initial engineering analysis. These determine the production requirements and leak standards to be achieved so that quality engineering of test solutions can begin. The first step in this process is to select the leak testing method that is the best match to application requirements.

In this “Leak Testing 101” series we will discuss the various dry air leak testing methods and the issues and techniques that affect testing costs and gauge repeatability and reproducibility (GR&R).

First, let’s take a look at the pros and cons of pressure-decay testing.

The big plus of pressure-decay testing—or at least the thought behind it—is that the leak detectors for pressure-decay leak testing have the lowest upfront cost. It is probably for this reason that the method is still in use, although in many applications the real costs of pressure-decay testing are actually much higher than many realize.

In the pressure-decay method for leak testing (see figure 1), a part is pressurized, the test circuit is isolated, and the pressure drop associated with a leak is measured. A transducer reads the pressure change. Calculations then convert these time/pressure readings into a measure of leakage rate. The higher costs of pressure-decay testing stem from the difficulties inherent in the test methodology. Pressure-decay leak testing is relatively difficult because measurements are highly vulnerable to changes in testing conditions such as drafts or temperature and there are often difficulties in determining the volume of test parts and test circuits, which must be known in order to calculate results.

Pressure Decay Method of Dry Air Leak Testing

Pressure Decay Method

Also, pressure-decay leak testing requires two measurements of pressure with sufficient elapsed time between measurements. When speed of testing is an issue, this built-in delay makes the pressure-decay method less desirable. More important, the two measurements and the time lapse significantly increase the potential for measurement error. The amount of time you need to wait between measurements varies. Sometimes, long intervals between measurements can make for extreme accuracy, but these long wait times are typically not practical. The larger the part volume, the longer it takes to measure the pressure drop. Moreover, very large flows are also impractical with pressure decay, because when pressure drops very fast, it will probably not be measured accurately.

Thus, although pressure-decay leak testing instruments have a relatively low upfront cost, the extra time it takes to perform testing (if the results are reliable enough for the given application) is another expense that needs to be factored in to overall cost. It can still be the best leak test method for a specific application, but the trend lines are in the other direction. Most applications now require tighter GR&R even for very low leak rates, often with large volume parts, and with a desire to keep test cycle times to the bare minimum to cut overall testing costs.When you factor all these considerations in, it often leads one to use other leak test methods instead.

In the upcoming issues of this “Leak Testing 101” series I will discuss differential pressure-decay testing, mass-flow leak testing, temperature compensation issues, and many other topics. By the conclusion of Leak Testing 101, my goal is to bring all quality managers up to speed on the real factors that affect leak testing cycle times, costs, and reproducibility.

If you would like your specific questions on best practices for leak testing (and other testing topics) to be discussed in future articles, please leave your comments and suggestions in the Comments area below.

ABOUT THE AUTHOR

Jacques Hoffmann’s picture

Jacques Hoffmann

Jacques Hoffmann is founder and president of InterTech Development Co., a world leader in test-centric assembly specializing in automated leak and functional testing with mass flow, hydraulic, helium, or pressure decay technology (ISO-17025 accredited). InterTech Development Co.-engineered solutions are used by hundreds of quality management, product design teams, and manufacturers worldwide and the company’s worldwide support organization maintains offices in North America, Asia, and Europe.

Note:  The above article has been reproduced from an article written by the author for Quality Digest

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