Understanding Air Compressors – Part 3

 [Note: Part 1 of this article presents basics of air compressors. Part 2 presents the classification and the construction details of air compressors. Part 3 presents a brief about the sizing of air compressors.]

Sizing Air Compressors

Sizing an air compressor for an application requires a logical sequence of actions. The following steps highlight a systematic approach for selecting the right air compressor.

1. Determine the air requirements of the application. Use the chart published by manufacturers to determine the average flow rate requirements [(lpm (FAD) or cfm (FAD)] of every air consuming device.

2. Once the air requirement of each of the air consuming devices has been determined, calculate the total air requirement of all the air consuming devices, allowing for leaks and future expansion.

3. Find the duty cycle of the application.  It is an attempt to find the number of hours the compressor is expected to run. For example, if 70% of the time the compressor is expected to provide air to the equipment, the amount of air to be supplied by the compressor would be 0.7 x the total air requirement as calculated in step 2.

4. Determine the required pressure (psig). Most actuators and air tools require 6 to 7 bar [90 to 100 psi]. Many other actuators and tools may require up to 10 bar [150 psi].

5. Check for the voltage and phase where the compressor is going to be located. This is a critical step in sizing and selecting the proper compressor.

6. Determine the compressor tank (receiver) size. Most manufacturers offer standard sizes based on the delivery of the compressor.

A Sample Air Consumption Chart for Automotive Service Shops