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Air Compressor Size and Selection Guide

Air Compressor Size and Selection Guide

An inefficient compressed-air system results in higher energy costs per unit of compressed air, improper or erratic tool operation, shortened component life, reduced capacity and the build-up of rust or sludge in the main and branch lines. Problems like these have the potential to cost businesses millions of dollars a year. In order to create an efficient compressed-air system, you’ll need to take into account the size of the compressor, as well as how to prepare and distribute the air.


Air Quality

Important factors to consider in achieving and maintaining air quality standards with air-cooled compressed-air equipment include:

  1. The location of the compressed-air equipment, which should be based on delivering the desired compressed-air quality and should:
    • Control the ambient temperature.
    • Supply the required cooling airflow.
    • Prevent negative air pressure.
    • Use ducts to remove exhaust heat.
    • Remove the radiated heat.
    • Recover any wasted heat.
    • Provide the correct airflow pattern across air-cooled compressed air equipment by installing intake louvers in the wall.
    • Position equipment so that the cooling fan exhaust is in the direction of the airflow.
    • Keep the outside of the air-cooled heat exchangers clean.
  2. When installing air-cooled compressed-air equipment, consider the pressure dew point of the compressed air exiting the air dryer, which is dependent on proper installation. Some symptoms of poor installations of air- cooled compressor equipment are:
    • High compressor operating temperatures.
    • Compressor shutdowns at high temperature.
    • High-discharge air temperature.
    • Reduced compressor output.
    • Increased refrigerant suction pressures on the air dryer.
    • Moisture downstream of the cleanup equipment.

Sizing an Air Compressor

Sizing an air compressor requires a logical sequence of steps to determine the proper amount of air for the application. The following lays out a systematic approach for making the right decision.

Step 1 Determine your air requirements. Use the chart below to determine your average CFM requirements per tool or check with the manufacturer. In the example below, we are sizing the compressor for a typical auto body shop.

Step 2 Once all the air requirements have been determined, total the CFM needed for the air compressor. In this example that would be 80 CFM.

Step 3 Allow for leaks and growth of the business.

Step 4 Duty Cycle: How long do you expect the compressor to run during working hours? In this example, 70% of the time you expect the compressor to be providing air to the equipment. (0.7 x 80 CFM = 56 CFM). This is the amount of CFM you would use to determine the proper compressor.

Step 5 Determine the required pressure (psig). Most air tools require 90-100 psig. Other tools, such as tire changers, require up to 150 psig. Check with your equipment manufacturers for psig recommendations on other equipment.

Step 6 Check for voltage and phase where the compressor is going to be located. If this information is not available, then have a qualified electrician check for voltage and phase. This is a critical step in sizing and selecting the proper compressor.

Step 7 Determine the compressor tank (receiver) size. Most manufacturers offer standard sizes based on the CFM of the compressor (the most popular sizes are 80, 120 and 240 gallon).

Sizing & Selecting an Air Compressor

_______ Impact Wrench, 1/2" Drive 3 _______
2 Impact Wrench, 3/4" Drive 7 14
2 Impact Wrench, 1" Drive 10 20
2 Tire Changer w/Inflator 4 8
2 Grease Gun 4 8
1 Oil Pump 4 4
Parts Washer ( Air-agitated) 2 2
4 Lift (in-ground) 8000 lbs ( Add 1 CFM
for each additional 1000 lbs.)
6 24
_______ Air Jack 4 _______
_______ Cabinet Blaster w/5/64 Nozzle 7 _______
_______ Cabinet Blaster w/1/8 Nozzle 15 _______
_______ Cabinet Blaster w/5/32 Nozzle 20 _______
_______ Other Tools/Equipment _______ _______
Total CFM in Service Shop 80
_______ "DA " Sander 12 _______
_______ 6" Grinder 10 _______
_______ Panel Cutter 8 _______
_______ Plasma Cutter 6 _______
_______ Spray Gun, Touch-up 4 _______
_______ Spray Gun, Professional 9 _______
_______ Spray Gun, HVLP 11 _______
_______ Paint Shaker 3 _______
_______ Respirators (Per Man) 4 _______
_______ Other Tools/Equipment _______ _______
Total CFM in Service Shop _______

Total CFM required for all tools/equipment listed @ 100% duty cycle: 80 CFM

Total CFM needed = 80 CFM x 0.7 (duty cycle): 56 CFM

Note: All above tools/equipment operate at approximately 90-100 psi, except tire changers air jacks and in-ground lifts, which will operate faster and more efficiently on pressures up to 150 psi.

There are several different Speedaire compressors to fit this application. consult the Grainger catalog for details.

Other items to determine:

Electric motor voltage 200-208, 230, 460
Electric power phase single, three
Compressor tank size 60, 80, 120

The product statements contained herein are intended for informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness for a specific application or use. W. W. Grainger, Inc. does not guarantee the result of product operation or assume any liability for personal injury or property damage resulting from the use of such products.