But depending on the way you use your compressed air, and how the compressor is installed, the operating costs may be quite different for the two choices—and not in the way you might think.
Reciprocating compressors use pistons to compress the air to the line pressure you desire. You can certainly tell when they are running, because the pistons create a lot of noise. The cooling systems of these units are typically just fins across which a pulley mounted fan blows a stream of cooling air.
The air produced by these units is usually very hot and oily—difficult to clean and dry unless some sort of auxiliary cooling and filtering method is used. If one looks up the efficiency of these units, you may find that at full load they consume more power per unit output than a screw compressor usually rated in kilowatts per cfm, called specific power. Screw compressors, on the other hand, are more complex and expensive units and can often be mounted on the same sized storage tank.
Screw compressors are much quieter than reciprocating units and have very good cooling systems, similar to automotive radiators across which passes cooling air generated by a fan. These units are designed to run at full load and will produce much cooler and cleaner air, which can be sent directly to an air dryer to remove water vapor. These units usually consume less power per unit output at full load than reciprocating units, making them more efficient in that condition.
But compressors running in a service shop rarely run constantly at full load. Experience has shown that compressors in this type of duty often run at average flows of 10 percent or less. And when one tracks the energy consumption of both types of compressors at this low load quite a surprising picture emerges. Request a Quote. Learn About Air Treatment. Browse Screw Compressors. Fixed Speed Compressors. AIRnet Piping System. Variable Speed Compressors. Get in touch for compressors! Get a quote for a compressor Get a quote for an air treatment product Parts and service request Request technical assistance.
Get in touch for tools! Get in touch for construction equipment and mobile energy! Follow us on social media Linkedin YouTube. One advantage over reciprocating compressors of the same horsepower is they operate at cooler temperatures. Installation Small reciprocating machines should be used with an air receiver. The receiver stores compressed air and minimizes the loaded run time of the compressor. It is particularly important to the life of these compressors to use an adequately sized receiver.
No matter what the receiver size or configuration of the compressor and receiver, small reciprocating machines are relatively easy to install. Any reciprocating compressor should always be anchored to the floor due to unbalanced forces. The majority of small rotary packages are designed to stand alone. Base-mounted units can be mounted on top of an air receiver.
Air is discharged from rotary screw compressors without pulsations. However, it is a good idea to include a receiver in the system to smooth the control air signal back to the compressor controller and provide consistent operation. Small rotary screw compressors offer the purchaser a good value for a complete package that can be used in applications demanding constant volumes of compressed air. Most enclosed rotary units operate at sound levels well below 80 dBA.
Packaged rotary compressors are easily installed by using simple floor anchors, and generally have single-point hookups for electrical and air connections. Selecting the correct installation space for an air-cooled compressor is an important factor for reliability and long service life. Good airflow over the compressor pump is essential for the unit to operate properly and extend service life. Overall, compressed air quality from rotary screw compressors is good.
Air quality is further improved by lower operating temperatures that are inherent to the rotary design. Most rotary compressors operate at approximately deg F above ambient temperature.
Oil free, oilless, or non-lubricated Which compressor should be used in applications where air or gas is required to be free from oil? Oil-free compressors use some form of lubrication for bearings and gears, but the compression area is free from oil.
Oil-free compressors are often rotary screw. These oil-free machines, because of the lack of cooling at the point of compression, can run at elevated operating temperatures. Newer technology injects water into the compression area to keep operating temperatures down and extend service life.
Rotary screw, oil-free compressors range in size from hp and are used in applications of psig or less. Oilless reciprocating compressors are used primarily for applications from hp. Oilless compressors do not use any oil in the entire machine. Non-lubricated reciprocating compressors are a viable selection for higher pressure or higher horsepower applications.
Edited by Joseph L. Foszcz, Senior Editor, , j. The authors are available to answer questions on deciding which type of compressor to choose. They can be reached at The company website is www. Related info. Gears and Bearings Rotary screw or reciprocating air compressors: Which one is right? Businesses are well aware of the need for compressors, but there is considerable debate as to which of the two most popular types -- rotary screw or reciprocating -- works best in an application.
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