Compressed Air Best Practices - May 2008 - (Page 20)

| 05/08 Compressed Air Industry AUTOMOTIVE ASSEMBLY | HOW TO AVOID THE MOST COMMON BUS/ COACH KNEELING FAILURES thus causing a leakage failure. Eventually the damage will be so great that a life cycle failure will result. Seal shrinkage due to extreme cold can also cause the valve to not seal properly, thus resulting in a leakage failure. Dryers not installed and maintained properly in the air system that operates the kneeling module can also cause life cycle failures. Water in the air lines freezes when the temperature falls below 32°F (0°C) and causes the internal components of the module to no longer function because they have frozen together. Regardless of a kneeling module’s ability to operate in extreme temperatures, an effective system must be provided (and maintained) to dry the system’s compressed air. Unless moisture is removed from compressed air, it will condense as liquid water in the lines and cause line and component damage when it freezes. Even if freezing doesn’t occur, water in the compressed air stream can wash away needed lubricants in cylinders and valves causing equipment malfunctions and premature component failure. Many kneeling system manufacturers claim that their product will perform in extreme temperatures, specifically -40 °F. The question is how well? The only way to know for sure is by conducting a series of low/high temperature endurance tests that best simulate the real world conditions the module will be exposed to during operation. This test was performed on 10 kneeling modules. Testing Method — Using 10 kneeling module,24 temperature tests were conducted. Six 3-station 24VDC and four 4-station 24VDC units were used for this test. With 100-psi air to each module’s supply port, 6.5 cubic inch volume chambers connected to the right airbag and leveling valve ports, and 3 cubic inch chambers to the left airbag and leveling valve ports, the tests measured for leaks under the following conditions: p p This extreme hot temperature cycle simulates summer operation. Figure 2: Temperature test set-up Room temperature Low temperature and high temperature profiles; with and without a dryer Six- to eight-day duration cycling tests at different temperature profiles Sticking tests at different temperature profiles p p This extreme cold temperature cycle simulates winter operation. As noted, the hot temperature profile shown in Figure 3 was used to simulate summer operation. The cold temperature profile shown in Figure 4 was used simulate winter operation over a 24-hour period. The temperatures ranged from -40 °F (-40 °C) to 158 °F (70 °C). All supply ports for each module were connected to a distribution manifold to allow total leakage to be checked individually by a flow meter. A Programmable Logic Controller (PLC) was used to time the exhaust from the modules to minimize air pressure spikes inside the chamber. 20 www.airbestpractices.com http://www.airbestpractices.com

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Compressed Air Best Practices - May 2008 Contents From the Editor Utility-Air News The Compressed Air Audit of the Month Pneumatics Real World Best Practices Delta Industries: Doing What is Right for Customers Delta Industries: Six Truths You Need to Know about Really Putting the Customer First Power Supply Industries Resources for Energy Engineers Wall Street Watch Advertiser Index Job Market

Compressed Air Best Practices - May 2008

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