Choosing an air compressor can be difficult, but it doesn't have to be.

Price, functionality, and warranty are all factors to consider, but also you need to buy a compressor that is the most suitable for you particular intended use.

Step 1.Find out your tool’s air requirement:

You need to know the air requirements or cubic feet per minute, or “cfm”, of the tools you are using. Some tools use more air than others. Pneumatic nail-guns and staplers use smaller amounts of air, while air grinders and sprayers use larger amounts. Preety much all air tools have a usage rating for cfm consumption at a recommended PSI. This can usually be found on the tool itself or in the owner’s manual.

Using only one tool at a time? If you are the only person using the compressor, find the tool you will be usiing that requires the largest cfm. Use this cfm to figure out the size of compressor you need.

Using more than one tool at a time? If you will be using more than one tool at any one time, add up the cfm for all the tools that will be used at the same time (from largest cfm to smallest) and use this total cfm to figure out the size of the compressor you need.

Now you know the required (delivered) cfm you need.

Tip: If your tool operates well below or above 10 psi, you should keep in mind that as you drop in PSI usage you get a slightly higher cfm and vice versa.

Step 2. Look at the compressors “Delivered” or “Free” CFM Rating, not “Displaced” cfm:

To find the right compressor, you will need to understand the difference between “displaced” cfm and “delivered” cfm or “free” air. The "Displaced" cfm rating is the result of a mathematical equation (Bore x Stroke x Rpm) It is a measure of the cfm produced by a compressor working in a perfect environment at 100% efficiency.

This can be misleading. No compressor ever made is 100% efficient! So ignore that rating and go by the “delivered” cfm.

Step 3. Select the best compressor for your needs:

Take the required cfm in step 1 and add 20 percent. This is the number you will use to make your selection. Match up this new cfm with the “delivered” cfm rating for the compressor. The closest matching compressor is your best choice.

Does Compressor Horsepower Rating Matter?

Absolutely not.

An air compressor requires a motor to power the process of producing air. The motor's horsepower is not the only component in the equation. The motor works with the compressor pump that it runs, which in turn produces the air needed. More horsepower does not necessarily mean more air. You must keep your required cfm in mind. Adequate horsepower combined with a quality pump is what produces enough cfm for your needs.

WARNING: When shopping,look at the compressors running horsepower and not the peak horsepower. Peak horsepower is what you get at startup.

The surge of power needed to start the motor can be 1.5-3 times the amount of running power needed. This means the horsepower need for the motor peaks, then drops down to normal. Many manufacturers are involved in class-action lawsuits for misrepresentation.

How many volts do I need to run on?

Most direct-drive electric compressors will run on a standard 110-volt circuit. With electric wheelbarrow compressors, you may have a choice for a dual-voltage option, which allows you to switch between 110-volt and 220-volt, depending on power supply that is available. For jobs that require a lot more air, a 220-volt motor will be the only choice if a gas-powered compressor is not an option.

Can I run my air compressor on a generator?

Don't ever use a generator to power your compressor if no power is available at the jobsite. Serious damage will be done to your compressor motor from fluctuations in power from a generator. The manufacturer can easily find damage that occurred because the compressor has been run on a generator, and it will void any warranty you have.

Consider using a gas-powered compressor if no power supply available, or the power is far away. And always use the suggested length and gauge power cord suggested in the owners manual. Remeber this as well: Use a longer and larger diameter hose rather than a longer power cord! Your compressor will last much longer!

Compressors need more power to start-up than they need to run. Many times the power needed for start-up is 3 times the amount needed to run. This means the amp-draw is 3 times as much too!

Should I buy a Stop-Start, or a Constant-Run compressor?

First, what is the difference between “stop-start” and “constant-run”?

Stop-Start: With this type, a pressure switch is used to automatically turn the compressor on and off at pre-setlow and high-pressure levels. When on, the tank pressure builds to a certain psi (pounds per square-inch) and then turns off. As air is used, the psi in the tank drops and eventually reaches the level where the pressure switch automatically turns back on. It then builds the psi back to the high point. This type is common for smaller electric, direct-drive compressors.

Constant-Run: With this type the motor continues to run and turn the pump. When the tank reaches the high-pressure (psi) setting, a valve opens to so the compressor can continue to run. The valve automatically closes again when the psi reaches the low point to direct air back into the tank and build pressure back up to the high point. This type is used more often when using tools that require a heavy, constant air flow without interruption An example would be an air grinder or sander or sprayer or even a crew of five people roofing a house.

Tip: If a compressor stops and starts 20 times per hour or more, you should be using a constant-run type. If you don't, you're in danger of ruining the compressor motor from the excessive heat. Stopping and starting a motor creates a huge amount of heat, a lot more than heat than a constantly running one.

Compressors with a “dual-control” option built in let you switch back and forth between stop-start and constant-run depending on the situation. These are a good bet if your situation varies a lot.

All gas-powered compressors have an unloader-valve (Constant-Run) system because a gas engine cannot stop itself and start up again. It can only idle down and up at set psi levels via a throttle-control.

What size tank does my air compressor need?

Tank size is a factor for one reason: A compressor will run until the tank pressure builds to the high-pressure point. The bigger the tank, the longer it takes to use up the compressed air. Once the air is used up, it takes a long time for the air tank to re-pressurize. A large tank is an option if starting and stopping too often is an issue, or if you need constant flow of air in longer intervals. You basically have a choice between larger tank and constant-run.

Should I buy an “Oil-less” compressor?

Compressors have a pistons that pump up and down inside their individual cylinders and compress the air to build pressure. This creates friction and heat. Some pumps are “splash” lubricated with oil and some have a teflon-type lining in the cylinder to reduce friction.

Oil-less compressors are fine for light use and have the advantage of being able to run on un-level surfaces without worry, but though they low-maintenance, they wear much quicker besause of more heat build-up and repairs could be expensive.

Oil-lubricated compressors keep the pump running cooler and last much longer. They are built for the professionals who will use them extensively. You must, however make sure the compressor sits level so the “splash”-lubrication is reaches all cylinders. If run on un-level ground, it can do a lot of damage over a short period of time. This is considered abuse by the manufacturer and will not be covered under the warranty.

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