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 4

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In parts onetwo, and three of this “Leak Testing 101” series, we discussed three methods of dry-air leak testing—pressure decay, differential pressure decay, and mass-flow leak testing—including the pitfalls and hidden costs inherent in two-step pressure testing methods and the higher accuracy of single point measurement mass-flow leak testing techniques.

 Is mass-flow leak testing always the best leak testing method? Absolutely not. When accuracy and cycle time requirements are not that stringent, pressure decay testing or differential pressure decay testing can be a better application match because test instrumentation does not require as much specialization and related cost. At the other extreme, when very small leaks of less than 0.01 standard cubic centimeters per minute (sccm) must be detected, helium mass spectrometer leak testing methods may be required. It is the only reliable method when an application requires detecting leaks as small as 10–4 standard cubic centimeters per second (sccs) or less.

There are several different helium leak detection methods:

Sniffer—The test item is pressurized with helium and an operator moves a sniffer probe connected to the mass spectrometer to localize the leak. This method is slow, nonquantitative but has the advantage of localizing the leak.

Accumulation—The test item is placed in a chamber and charged with helium. Helium leaking from the part accumulates in the chamber and after a certain amount of time, a sniffer probe checks for the presence of helium, i.e., a leak. While apparently inexpensive, this method has a number of shortcomings: presence of tracer gas from prior tests, lack of adequate circulation in the chamber, and long test times due to background effects. As a result, it will be difficult to provide quantitative testing with this method.

Vacuum leak testing with helium—Figure 1 shows how helium mass spectrometer leak testing proceeds. The part is pressurized with helium and the chamber is evacuated down to less than 0.1 mbar absolute to eliminate background effects. The presence of helium leaking into the chamber is then detected by the mass spectrometer.

Helium Mass Spectrometry Method of Leak Testing

Figure 1: Test item is pressurized with helium within a test chamber. The chmber is evacuated, drawing helium out of the leaking test item. Mass spectromter then samples the vacuum chamber.

Equipment costs, maintenance costs, extra time required to evacuate helium from test fixturing in between test cycles, and ever rising helium costs makes this method the method of last resort. Typical applications include: heating, ventilating, and air conditioning (HVAC) components; pace makers; aluminum wheels; and airbag components.

For these type applications where leaks of 10–4 sccs or less must be detected for product integrity or safety, helium has its well-deserved place in the repertoire of best-match leak test techniques to consider.

In the next part of this Leak Testing 101 series we will discuss miscellaneous other testing techniques including: hydrogen ultrasonic, bubble testing, and air under water.

If you would like specific questions on best practices for leak testing (and other testing topics) answered in future articles, please send me your questions at jhoffmann@intertechdevelopment.com.

 

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

 

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Leak testing 101 – Part 2

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In part one of this series, we considered the pros and cons of pressure-decay testing. In part two, we’ll take a close look at a leak-testing method called “differential pressure decay.”

This method is similar to simple pressure-decay testing discussed in part one.A more accurate variant of the pressure-decay method, differential pressure testing involves pressurizing a reference volume along with a test part. The pressure differential between the non-leaking reference volume and the test item is then measured by a transducer over time, as shown in figure 1. This method requires measuring pressure at two points in time to obtain a pressure change reading. It is an indirect method of measuring leakage rate because the time and pressure data must be converted into leakage rate. This method allows you to use a higher-resolution pressure transducer.

Differential Pressure Decay Method of Leak Testing

Differential Pressure Decay

Figure 1: With valves 1 and 2 open, the test item and reference volume are pressurized and then isolated by closing valve 1. The reference volume is then isolated from the test item by closing valve 2. The transducer reads the pressure differential between the reference volume and test item twice over time.

A down side to this method is that the larger the volume, the smaller the change in pressure for a given leak rate, resulting in longer test times as test volume increases. All temperature effects are the same as for pressure decay.

Differential pressure-decay testing is widely used. Unfortunately, in many instances it is the default choice of manufacturing and quality engineers who don’t understand the true cost of this type of testing. They could eliminate these hidden costs by using mass-flow leak detectors, another dry air-leak testing method that will be discussed in part three.

Moreover, the indirect nature of the test process and the time needed to track pressure changes and take two measurements create inherently longer testing times. This means a greater probability of measurement error exists than for methods that require only one measurement. The probability of measurement error is directly related to the interval length between the two measurements. These factors are what lead many technicians to use mass-flow leak testing.

That said, it should be noted that for many applications at pressures in excess of 150 psig, differential pressure-decay leak testing remains the method of choice. Granted, test cycle times are slower than with single-measurement leak test methods, however, this drawback is outweighed by the lower costs for instrumentation. Basically, choosing between pressure decay or differential pressure-decay test methods involves a trade-off between cycle time and instrument cost.

In part three of “Leak Testing 101,” we will discuss the mass-flow leak testing method: how it works, and the pros and cons vis-à-vis helium and pressure-decay testing. I’ll explain how to implement this technique to get accurate gauge repeatability and reproducibility (R&R).

If you would like specific questions on best practices for leak testing (and other testing topics) answered in future articles, please send me your questions at jhoffmann@intertechdevelopment.com.

Note:  The above article has been reproduced from an article written by the author for Quality Digest
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Learn more about turnkey hydraulic testing systems

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When your production focus is vehicular manufacturing—automotive, diesel or off road—there is no shortage of challenges when it comes to hydraulic testing.

Quite often one is dealing with a high production rate requirement usually in excess of 150 parts per hour. Conversely, individual part test time must be completed in a matter of seconds.

Blink-of-an-eye production rates ensure that traceability is a fundamental necessity and, combined with a programmable marking system, remain a manufacturer’s most important quality control ally. But ensuring that you have such systems in place is another challenge.

Overlaying these issues is the reality that today you are likely manufacturing for global markets. So for example, while durability and reliability are always issues, they are even more so when a given part you are testing in-line has to be as reliable in Quebec as it is in Qatar.

Clearly, manufacturers who rely on an automated, up to date turnkey system for hydraulic testing are sleeping better this evening. So what do these systems look like? And what are the key features and benefits justifying the investment you will make in a turnkey system? Let’s consider a few applications that explore these questions.

The first functional test stand automatically tests, marks and sorts hydraulic solenoid valves. Of course, the hallmark of a forward thinking turnkey system is flexibility, so this modular design accommodates future product configuration changes.

In operation, the solenoid valves are automatically transferred from the test station to the marking station where programmable marking automatically identifies each part for traceability.

Then on to the unload station for classification based on test results; in this case there are three accept bins and one reject bin. Rejects are automatically unloaded into a separate bin with discharge verification to eliminate the possibility of shipping defective product. Test data is stored by serial number to document the supplier’s quality assurance program for a series of Six Sigma moments a QC manager would have to admire.

For maintainability, ready access to all machine components is provided. And today’s turnkey system must be user friendly. This one incorporates a Windows test program to allow the authorized engineer to easily change all test parameters (accept/reject levels, duty cycle, duty cycle increments) and interface with LAN data collection devices.

A turnkey system such as this one gives a manufacturer complete control and management of a hydraulic test station.

Relief Valve Hydraulic Functional Test Stand

This turnkey system is built for speed—automatically testing, marking and sorting a family of valves at 152 pph. Temperature control of the test fluid was critical for accurate testing, and to meet automotive industry requirements for test R&R. So a closed loop system was designed to maintain consistent fixture temperature (100 F ± 3 F).

The instrumentation performs eight tests:

  • unseat (1,600 psig) and reseat (1,400 psig) at minimum flow
  • pressure at maximum flow
  • low pressure integrity test at 20 psig
  • high pressure leakage at 2,000 psig max
  • low pressure at 100 psig max
  • internal seat leakage of 900 psig
  • O ring check at 6 psig (air test)

What goes into this high-speed system? At its heart is modular instrumentation for flexibility and ease of maintenance. Test parameters are programmed to meet industry requirements, automatically selected, and sequentially performed. Dial transfer of parts, automated handling and sequencing of tests minimizes cycle time.

Through a fail-safe protocol, only accepted parts are marked, while automatic unloading and sorting prevents rejects from continuing down the production line. Reliability, which is always an issue, is ensured by repeatable positioning, a barrel cam indexer and interlocked motions. As in the prior example, tests may be easily modified through Ethernet connectivity to meet changing customer conditions and requirements.

Safety is always a concern when fluids are in the mix. So the stand is designed to contain oil spillage. Redundant monitoring systems are part of the design as well, shutting the machine down in case of heater failure or excessive pressure loss.

Finally this hydraulic test stand and turnkey system incorporates SPC capabilities. Test results and stats are displayed on a monitor in real time and sorted on disk in spreadsheet compatible format for analysis.

Testing Design Requirements

If design requirements for a hydraulic test are unclear, incomplete or somehow inadequate, trouble brews. What do clear and well thought out design requirements look like? Consider this example for a high pressure valve performance test.

Safety first is job one in a test where extremely high pressure is demanded to accurately measure incremental flow force. So the enclosure is designed and interlocked to ensure operator safety with a part under test at 40,000 psi.

All hydraulic lines from the pump to the fixture are contained in a separate housing to protect against ruptures. A liquid air over oil intensifier is used to bring the 0.5 liter rail volume up to test pressure.

A test stand should be designed with ease of operation in the forefront. So the intensifier drive air regulator is brought to the front of the machine for easier operator adjustment. A pressure relief valve is provided on the drive air regulator to ensure the maximum hydraulic pressure is not exceeded, and a small hydraulic pump is required to replenish the rail volume in between tests. A small air to oil cooler is incorporated to keep hydraulic fluid temperature at factory ambient temperature 72 to 104 F.

Finally, the fixture must work under extremely high pressure and measure flow force on valve stem lifts in increments of 0.005 millimeters. In this particular scenario, it consists of the following steps:

Implement a Piezo-electric load cell to reduce the compressive distance to 1 micron/1.05kN.

  • Accurately measures the fixture and valve stem compression and provide 10 valve lift stops in 5 micron increments.
  • Position the valve preload spring above the solenoid so that it will not influence the test system.
  • Program the data acquisition computer for the Piezo electric load cell.
  • Provide data collection points for all sensors with adjustable target time and averaging width.

In the final analysis, hydraulic testing is always challenging. But with a well thought out plan for a turnkey system, thorough preparation, clear design and testing requirements, you can reach the high product quality standards that your company aspires to achieve.

Full article details – click here IDC-Quality NDT-Article-2012 Turnkey hydraulic testing systems

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