What size air compressor do I need?
Figure out your tool's air requirements.
All air tools have a force air requirement, measured in pounds per square inch (psi), and a volume requirement, measured in cubic feet per minute (cfm). Air requirements vary between types of tools and even between manufacturers. You should always check the owner's manual to find a tool’s air requirement, but the chart below gives a general range of the pressure and volume requirements of different classes of tools.
Check the compressor's CFM Rating
A compressor must at least meet the maximum cfm of your specific air tool. This capacity should be sufficient for occasional use of most air tools, and frequent use of tools that “burst” like nail and staple guns. If you need your tools frequently, use multiple tools simultaneously or have “constant use” tools like random orbit sanders, then increase the cfm requirement.
Most compressors will list their cfm at 90 psi or 120 psi. These are simply baseline values that represent using an “average” tool. If your tools require significantly less or more than the displayed psi, check the compressor’s owner’s manual. It should have a complete list of the compressor’s cfm at different psi’s.
If you need to power several different pneumatic tools, use the tool with the highest force air requirements when picking your compressor. If you need to power several different tools at the same time on the same compressor, then you should use the total sum of the tools’ force air requirements when picking your compressor. (For instance, if you need to run a 4 cfm @ 90 psi air gun and a 5 cfm @ 90 psi sander at the same time, then you need a compressor that produces at least 9 cfm @ 90 psi.)
Note: When checking a compressor's cfm, look at the “Delivered cfm” or “Free cfm” rating. Do not use the “Displaced cfm”. Displaced cfm is the air flow the compressor produces in a perfect environment working at 100% efficiency. But no compressor is 100% efficient, no matter how new, and most jobs sites aren't “perfect environments.” The “Delivered cfm” rating will give you a more reliable representation of how the compressor will typically perform.
What size air tank do I need?
There are no hard and fast rules for choosing a compressor’s tank size, but we suggest you get the largest, practical tank you can afford. There are two main reasons why bigger is better when it comes to air tank size: motor strain and condensation.
A compressor uses its motor or engine to help fill its air tanks with compressed air. When the volume of air in the tank falls to a certain point, the motor will switch on and begin to fill the tanks again. Frequently turning off and on strains the motor, and shortens the life of the compressor. Because smaller air tanks hold a smaller volume of air, they need to be filled more frequently, and so they switch on their motors more frequently. A larger tank means you can use your tools for longer periods of time before the motor must switch on again. This reduces strain on the motor and prolongs the life of the compressor.
When air is compressed, it becomes hot and holds more moisture. If compressed air is used when it’s still warm and full of moisture, condensation can build up in your air lines and damage your compressor and tools. If the air tanks are too small for your needs, the compressed air will be used right away, before it has cooled. Larger tanks hold the air for longer, giving it a chance to cool and release moisture before entering the air lines.
We should note that a larger air tank adds bulk, weight and cost to a compressor. Despite these issues, we still recommend getting the largest practical size tank you can afford. (A 20 gallon tank will hold a lot of air, but it will also be hard to move from job site to job site. You must decide what “practical” means for you).
While there are several factors to consider, don’t get caught up in trying to calculate the “perfect” size air tank. Remember, cfm and hp are the most important elements when comparing compressors. Once you’ve narrowed your selection, tank size may be one of the factors that help you make your final decision.
Note: The drawbacks to smaller tanks are important for people who use their air tools frequently. If you plan to use your compressor for household tasks and occasional small projects, these drawbacks are not significant concerns.
Does an air compressor's horsepower rating matter?
Yes. In a nutshell, horsepower can improve a compressor’s recovery time, but it won't make your nailer any faster or more powerful.
Horsepower (hp) in a compressor refers to the power of the engine or motor. The motor powers the compressor pump, which fills the tank with compressed air. Higher horsepower can help the pump fill the air tank more efficiently, reducing your recovery time. However, horsepower does not affect airflow from the tank to the tool. The cfm and psi ratings are more important when it comes to powering your tools.
The bottom line: when selecting your compressor, don't sacrifice a good cfm rate for lots of horsepower; you won't get the performance you need.
Note: When checking a compressor's horsepower, look at the “Running Horsepower” and not the “Peak Horsepower”. Peak horsepower represents the surge of power a motor has when first starting and can be 1.5 to 3 times the amount of power generated during normal operation.
Can I run an air compressor on a generator?
We do not recommend using a generator to power your compressor. Air compressors can be seriously damaged by the generator’s sudden fluctuations in power. This is considered “improper use” by most manufacturers, and it will void the warranty. If you routinely work in areas without a reliable power supply, a gas-powered air compressor may be the best option for you.
If you are having difficulty powering your electric air compressor, make sure you are using the correct length and gauge of power cord. (The owner’s manual should provide this information). Cords that are too long are less efficient at supplying power. It’s always better to use a shorter extension cord and a longer hose.
I have more questions!
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