10 questions to consider when purchasing an air compressor

When deciding upon an appropriate air compressor for the shop, officials at Ingersoll Rand, a world leader in creating and sustaining safe, comfortable and efficient environments (www.ingersollrand.com), recommend answering 10 essential questions.

1. What are you using the compressor for? Do you run the compressor consistently throughout the day or occasionally?

Also pay attention to the duty cycle required. The air compressor needs to meet or exceed that duty cycle in order to function properly.

2. Where are you going to put the compressor? If it’s outside, you’re going to need a compressor with special protection against water and cold temperatures. Ventilation is also key, since most reciprocating compressors are air-cooled.

3. How much pressure do you need? Pressure, measured in pounds per square inch (psi), provides power to tools. Determine the tools that you use that need the most air. The compressor should be able to provide at least that much psi.

This will also help you determine if you need a single-stage or two-stage compressor.

4. How much air flow do you require? The amount of air the compressor creates is measured in cubic feet per minute (CFM). However, the important measure is ACFM (Actual Cubic Feet per Minute). This is the most accurate measure of usable air available for work.

When considering a compressor, make sure you know if the CFM rating reflects ACFM or piston displacement (PD) at a specified psi.

5. How much horsepower do you need? Horsepower is important, but it’s directly proportional to the cfm rating discussed previously. The higher the horsepower, the more air the machine can produce.

As such, compressors that claim high horsepower but low air flow performance typically run hot with a shorter lifespan. These are occasional use compressors and not ideal for a shop setting.

6. What size air tank do you need? Compressors with smaller tanks have to work harder to keep up with air demands, so be sure to match your air demands with the tank size.

You’ll also need to decide if you would prefer a horizontal or vertical tank, and this has a lot to do with personal preference. For example, vertical tanks take up less space but are only available on models rated up to 10 horsepower.

7. What features should you consider? In addition to tank size, pressure and air flow, other decisions need to be made when purchasing an air compressor. Understanding the additional features and the benefits they provide will ensure you’re acquiring the most appropriate compressor.

For more demanding applications, like outdoor use or those in colder temperatures, options include 100 percent cast-iron construction for additional reliability and durability, stainless steel finger valves to eliminate corrosion, one-piece connecting rods to eliminate internal adjustments, oil-monitoring devices to prevent damage from low oil levels and separate cast cylinders for better cooling and extended life for two-stage compressors.

It’s also important to remember that fewer moving parts should reduce maintenance costs.

8. What electrical requirements will you have during installation? It’s important to know what voltage you have. Be sure to check both your voltage and horsepower to make sure your electrical service supports the air compressor you are considering.

9. Do you need control systems, and what kind? There are three control systems to consider: Start/Stop Control, Constant Speed Control and Dual Control. Start/Stop is ideal for applications that don’t require continual air.

Constant Speed keeps the compressor from excessively starting and stopping. If a compressor starts more than six to eight times per hour, you should operate Constant Speed Control. If less, opt for Start/Stop Control.

Dual Control lets the user choose between Start/Stop and Constant Speed by adjusting the compressor auxiliary valve.

10. What else do I need to consider? Other important things to remember, regardless of what type of compressor you choose, include using the proper oil to ensure the long-term operation of the compressor, paying attention to moisture on your machine as it can be detrimental to the compressor (look into moisture removal products like in-line filters and moisture drains) and using the proper starter.