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There are two design categories, and you must thoroughly understand the workings of both before making a decision.
Compressors are mechanical devices that pressurize and circuiate a wide variety of gases (i.e., air, natural gas, oxygen, nitrogen and many types of refrigeration gases) for applications that include providing power for controls, maintaining tension, enabling chemical reactions, moving raw and finished production materials and supplying energy through pipeline transfer of gas to homes scattered throughout industrialized nations.
Without refrigeration compressors, the ability to supply food to entire nations would be lost. These same types of compressors make living in hot, humid climates more tolerable by supplying cool air for homes and offices.
There are many different designs that enable this work to be done. Each design has strengths and weaknesses that make it suitable for its respective application. Compressors may be classified according to the following output or discharge pressures:
* High pressure - greater than 2,000 kPa, gauge/290 PSlG
* Intermediate pressure - equal to 800-2,000 kPa, gauge/1 16-290 PSlG
* Low pressure- equal to 100-800 kPa, gauge/14.5-1 16 PSlG
There are two categories of designs: positive displacement and dynamic (continuous flow). Dynamic compressors, such as turbines and axial flow compressors, produce large volumes of relatively low pressure gas.
Last month we discussed the nature of positive displacement compressors and the lubricant selection criteria appropriate for positive displacement designs. This month we address the lubricant selection criteria appropriate for continuous flow or dynamic compressors and their designs.
TYPES AND DESIGNS
There are a variety of compressor types and designs. As shown in Figure I1 there are two categories of designs: centrifugal and axial. Some designs have characteristics of both.
CENTRIFUGAL COMPRESSORS
Centrifugal compressors are a common design found in industrial process and manufacturing applications. This design uses an impeller to accelerate the gas as it enters the compressor chamber. Some centrifugal compressors incorporate a drive gear coupled to smaller diameter-driven gears coupled to the fan shafts (see Figure 2). The drive gear accelerates the rotational speeds of the shaft mounted fan, which increases the energy potential of the gas.
Some centrifugal compressors have fans mounted on a common shaft direct coupled to a drive motor. In this instance, the gas energy potential is increased...