Understanding Air Compressors – Part 3

 [Note: Part 1 of this article presents the basics of air compressors. Part 2 presents the classification and 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 to 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 air-consuming device has been determined, calculate the total air requirement of all the devices, allowing for leaks and future expansion.

3. Find the application’s duty cycle. It attempts 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 would be 0.7 times the total air requirement calculated in step 2.

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

5. Check for the voltage and phase where the compressor will 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