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How To Use The Axial Compressor Table

Most axial compressors are designed to compress air, and this introduction assumes that your application will do so. If you plan to compress a gas other than air, further research is required.

To utilize this table successfully, you must have certain information available for your compressor application. The most important is flow.

The table is sorted on ascending INLET FLOW as measured in inlet cubic feet per minute. Inlet flow (ICFM) is capitalized because there are several different measurements of flow. If you use one other than the inlet flow used in this table, your selection will be incorrect.

Inlet flow is defined as the flow capacity of the compressor at its design inlet temperature (in Fahrenheit degrees) and design inlet pressure (in pounds per square inch, absolute, not gauge). Do not use standard cubic feet per minute (SCFM) as there are several "standards", all of which are based on arbitrary standard temperatures and pressures and which may or, more likely, may not match your inlet conditions.

Once you have the correct flow, you will need the discharge pressure in pounds per square inch absolute. It is assumed that the inlet pressure is atmospheric, minus any pressure drops through the inlet filter and silencer and any other devices upstream of the compressor inlet. Your required discharge pressure must be compared to the discharge pressure rating of the compressor. The design pressure rating must be equal to or greater than your requirement. You should not eliminate the unit if the discharge pressure rating is higher than required. Blade rows can be removed to reduce the discharge pressure. Even if the discharge pressure of the compressor is lower than required, check the design pressure ratio (pressure out divided by pressure in) of the unit and compare it to your required pressure ratio. It might be possible to re-hydrotest the compressor to raise its discharge pressure rating. However, don't arbitrarily assume that a re-hydrotest is possible, as it may not be.

Rotor and stator blade material must be compatible with any contaminants in your air. This point is very important for safety and reliability considerations. Casing material also must be checked for compatibility with any contaminants and with the inlet gas temperature. Low inlet temperature requires the use of special materials.

Two other key points to consider are the speed and rotation mandated by any existing driver. Matching the rotation is essential to the proper selection. Speed should match as closely as possible to maintain the design pressure ratio. If the speed required is to be higher than the original design speed, further checks must be made to ensure mechanical reliability and safety.

Using the above discussion points to narrow the selection of a compressor will help you choose one to focus on. There are other points that must be checked before an ultimate selection should be made but these checks will get you off to a good start. If you have any questions, please contact (Bill@eTurbomachinery.com) or (Warren@eTurbomachinery.com).