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RailMarket Reporter

Advantages of Rotary Screw Technology for Locomotives

Atlas Corp

Mr. Robert Eshelman
Vice President - Business Line Manager
US Industrial Air Division
Atlas Copco Compressor

Atlas Copco Compressors

On most large-scale modern locomotives, air compressors provide pressurized air for locomotive braking systems and various subsystems. Reciprocating, or piston, compressors have been the primary compressed air source for this use, despite the general industry-wide replacement of reciprocating compressors by rotary screw compressors in applications that require horsepower of 15 or higher.

Standard rotary screw compressors are designed for stationary operation in an industrial plant and cannot withstand the extreme stresses of locomotive applications. However, rotary screw compressors designed and engineered specifically for the unique challenges of locomotive applications are gaining wider acceptance because of advantages in size, weight, noise levels, oil-carryover and maintenance and rebuild considerations.

During locomotive operation, air compressors must withstand constant vibration, or g-shocks. In order to tolerate severe vibration, rotary screw compressor must incorporate special vibration dampers and durable packaging for compressor components. Additionally, the rotary screw element must feature shockless, non-wearing compression technology with significantly fewer wearing parts than a reciprocating compressor.

Because the rotary screw element is generally not equipped with valves, it has no mechanical forces that cause unbalance. With balanced compression, rotary screw compressors offer smoother, quieter operations

and lengthen the service life of the machine. Locomotives are only productive assets when moving, so compressor maintenance must be performed expeditiously. Rotary screw compressors use fewer parts than reciprocating compressors, requiring less and lower cost maintenance and greater overall reliability. Because rotary screw compressors for locomotives feature roughly 85 percent of the same parts used by industrial compressors worldwide, they offer superior field experience and components are readily available for easy replacement.

To withstand major temperature and weather fluctuations that often occur during locomotive service, rotary screw compressors utilize an air-cooled electric drive and compressor lubricating oil that is designed to function reliably in temperatures from -40 to 125 degrees Fahrenheit. And unlike reciprocating compressors that have an oil-carryover of 8 ppm that increases to 25+ ppm over time, rotary screw compressors have a low oil-carryover that does not increase over the life of a properly maintained compressor. Low oil-carryover and lower oil requirements generates higher quality air.

With a compressor package that weighs 1,000 pounds less than a reciprocating compressor package of comparable output and requires 50 percent less space, rotary screw compressors for locomotives are easier and less expensive to maintain. And because it utilizes a technology that has been the industry standard for over 50 years, it provides superior performance in reliability, ease of maintenance and air quality.

Atlas Copco Compressors

Information courtesy of Atlas Copro Compressors

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