Portable Air Compressor Basics: Proper Selection and Maintenance

Portable air compressors are versatile pieces of equipment. These rugged machines, however, are not one-size-fits-all, and, therefore, it is important to get the right compressor for the job.


Portable air compressors are versatile pieces of equipment. These rugged machines, however, are not one-size-fits-all, and, therefore, it is important to get the right compressor for the job. The primary factor when choosing a compressor is to determine what the compressed air is going to drive. Once the field technician knows the application, it's just a matter of matching the intended use to a specific compressor size. And, understanding the fundamentals of an air compressor-that would be pressure and volume-are important in proper selection.

Pressure and Volume

Pressure and volume are the two most important variables when selecting a compressor. Pressure is measured in pounds per square inch (psi) and flow is measured in cubic feet per minute (cfm).


When selecting the compressor, the first variable to investigate is the pressure rating. This can be derived from the particular model name on the compressor unit. Doosan Portable Power, for example, assigns a lettering system to each model in order to understand each unit's operating pressure output. For example, the letter P equals 100 psi; the letters HP equal 150 psi. The letters VHP equal 200 psi, and the letters XHP equal 350 psi.

Air Flow

The air flow of a compressor can also be identified by the model number on the compressor. Most manufacturers use the same numbering system for the air flow-cfm-so it is easy to identify the volume of air being delivered by the compressor. A compressor with a 185 in the model name, for instance, denotes a 185 cfm of machine.


After pressure and flow, the most important component of an air compressor is its engine. Most air compressors are rated as either continuous or intermittent duty. For continuous use, the ideal engine margin is 85 percent of its maximum rated horsepower. For intermittent use, 93 percent is the margin.

Of all components on an air compressor, the engine will have the highest amount of wear. Be sure to follow the engine manufacturer's recommended maintenance schedule.

Utility Applications

Compressed air can be used to operate air tools in utility applications, such as repairing electric, water and sewer lines. Compressors can also be used for line testing to ensure there are no leaks and determine whether a line is able to hold certain levels of pressure. Compressors are also often used for powering directional drilling equipment laying fiber optic cable.

Portable air compressors usually range in volume from 90 to 1,600 cfm and pressure from 100 to 350 psi. For the majority of these applications, a contractor needs a compressor in the 90 to 250 cfm range.

Tool Guidelines

Tools designed to be used with air compressors have a pressure and flow rating listed on them. By knowing those two numbers, it's a matter of selecting the compressor model that provides enough pressure and volume to run the tool.

Most utility applications, which include operating light pneumatic tools, require a compressor with at least 100 psi. The more tools expected to run off one compressor, the higher volume of compressor will be needed. Any compressor dealer will be able to provide the necessary cfm for each tool and can help determine which compressor size is needed to fulfill the requirements of the job.

Maintenance: An Ounce of Prevention

Air compressors are rugged machines and can handle rigorous environments, but they do require care and maintenance. A strictly followed maintenance routine will pay for itself in the long term with increased efficiency and jobsite safety. Here are general guidelines for maintenance best practices.

Daily Checks

Daily maintenance is probably the most critical, yet many times is ignored. Work productivity is important, but taking 10 minutes each day to check the air compressor is vital to ensure the machine continues to operate without disruption.

First, start with a general walk-around of the compressor, checking for leaks. Then check the oil and radiator coolant levels. Check that all gauges and lamps are in working order and drain any water from the fuel filters. Check the air cleaner service indicators and fuel/water separator drain. Clear out the pre-cleaner dumps, and make sure the radiator cap is secure. Finally, remember to ensure the fuel system is free of debris with enough fuel for the day's run.

Add a few extra checks to the daily routine. Fan and alternator belts should be inspected for wear. Check the battery for corrosion and secure connections. If the air compressor is a mobile unit, check the tires each time it's transported.

Monthly Checks

Every month, check the machine closely for wear. Parts may need to be replaced. Check the hoses and tire lug nuts. Make sure the automatic shutdown system is in good working order, and clean the air cleaner system, the exterior of the oil cooler and the engine radiator.

At 500 and 2,000 Hours

Major maintenance is determined by hours the unit is in operation. The 500-hour mark is when all filters need to be replaced; if the air compressor is operating in a dirty environment, however, air filters should be checked daily and replaced when necessary. At 2,000 hours, the separator element will need to be replaced. It may need to be replaced before 2,000 hours if the service air starts to fog or there is oil carryover.

Air compressors are designed to be flexible and dependable. In many instances, more is not necessarily better. When it comes to working efficiently and effectively with compressed air, it is important to consult experts such as the dealer to ensure a compressor is chosen with the right amount of pressure and volume to match the application.

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