Compressed Air Best Practices - May 2008 - (Page 25)

Compressed Air Industry AUTOMOTIVE ASSEMBLY | 05/08 | A Kneeling Module Designed for Reliability and Durability After careful examination of all modules used for each series of test, the following is a list of the key design considerations Figure 11: Cross-sectional view of identified that directly contributed an over-molded poppet assembly to the successful results discussed in the previous section. Single-Piece Anodized Body — This critical component of the module is the core to the entire design. The kneeling module’s anodized body, along with other internal aluminum components, allows it to withstand harsh environments. Much of the success of the modules tested was directly influenced by the anodizing process these modules underwent during fabrication. Other Observations — Precision machined internal parts, as well as, the stainless steel return spring, designed specifically for the transportation industry, also contributed to the testing success, and ultimately ensuring a long operating life in the field. A single body design allowed for the flexibility to build three or four station modules from one component. A one block design for both versions also resulted in the same bolt hole pattern and connections for test setup. As a result, labor costs for assembly can be reduced in the field due to fewer components, connections and tubing. Fewer connections equate to fewer leak paths than with multiple valve assemblies and fewer components to purchase. The module size was also an added benefit as it is easily able to fit in tight spaces. Also, the module was designed so that components can be easily replaced if necessary. Over-Molded Poppet Valve Design — Although listed second, this key design point is certainly just as important as the first, if not more. The life and performance of the kneeling module rests almost entirely on the performance of this component. The quality of design and manufacturing of the poppet valve can both influence the life cycle failure mode, as well as, the leakage. The poppet assembly was also the most affected by all three failure mode causes identified (temperature, contamination and vibration) and, as a result, was the most affected component during all the various tests conducted. Observations — This low-temperature compound, precision ground poppet design, versus a spool design, was much better suited for harsh environments. A special over-molded rubber was used on the valve, which is suitable for both low and high temperature applications, ranging from -40 °F to +158 °F. Since the valve was designed with fewer components, there were less possible failure modes as a result. Performance wise, the valve’s higher flow rate allows the bus to raise and lower at a faster pace compared to other modules observed. Low-Temperature Dynamic O-Rings — These seals, used in conjunction with low temperature grease, allow the module to operate at optimum levels in harsh transportation environments. As stated previously, the two dynamic o-rings along with the precision ground poppet are the most critical internal components that ensure the module will be able to withstand the temperature extremes and corrosive environments. Exhaust Protectors — These devices act similar to a check valve as they permit unrestricted airflow during system exhausting, but also prevent air and, more importantly, external contaminants such as dust, dirt, salt, water and snow to make their way back into the valve. Transportation-Grade Solenoid & Pilot Operator — As mentioned in the salt spray testing section, this same pilot operator and mobile solenoids (22-mm grommet with 18" flying leads) are used on both this module and another transportation rated inline valve. The solenoid and pilot operator are both temperature rated to -40 °F to +158 °F (-40 °C to +70 °C) along with voltage characteristics of +/- 30% of rated voltages. Additionally, the ruggedness of the pilot operators can be witnessed by their maximum pressure rating of 232 psig (16 bar). Conclusion While no controlled environment test will ever replace real-world application testing, the severity of the above series of tests shows that as the transportation industry continues to grow, the performance level of the products being supplied to OEMs needs to improve at a similar pace. For this reason, OEM bus companies and fleet owners are looking to companies that specialize in motion control systems, specific to the transportation industry, to develop better products with superior performance that will also simplify installation, reduce maintenance requirements and parts inventory, as well as, employ designs that consider space limitations. For more information regarding the products referenced in this white paper, please visit www.parker.com/pneu/kneeling www.airbestpractices.com 25 http://www.parker.com/pneu/kneeling 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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