Most air compressors are available in three-fourths to five horsepower with a variety of tank sizes up to 80 gallons. The capacity and use will determine the size of compressor you will need. In many cases, two horsepower or less will be adequate for projects around the house. Typical tank size can range from 2 to 20 gallons. Again, the type of project you plan to complete will give you better insight into how large a tank you will need.
When you are shopping for an air compressor, look for one that has been certified by the American Society of Mechanical Engineers (ASME). This is one of the best measures of quality and can be verified by an ASME certification sticker on the tank. Remember, not all compressors will be certified by the ASME, but some states require vendors only sell certified compressors.
When shopping for a new compressor, there are a few things to keep in mind. Compressors can be divided into two types. Oil based pumps, and Air-Cooled pumps. The oil based pumps generally run a little quieter and may last a little longer when properly maintained. The air cooled units have the advantage of being practically maintenance free. If you will be moving the compressor around a lot, (like from job site to job site, the air cooled unit would likely be your best choice. If the unit will be less likely to be used in various locations, then you may want to look to the oil based units. There are a number of features you should look for when purchasing a new air compressor. An ASME certified release valve will allow air to escape automatically if pressure in the tank exceeds the maximum. The valve will have a pull ring attached to it which allows you to quickly check for clogs or corrosion.
If your compressor has an oil-based pump, it should have an oil level sight glass. Other things you will notice are a tank pressure gauge as well as a pressure regulator and gauge. Each tool and each job will have a specific pressure requirement, so having the ability to adjust the pressure is a must. Most tanks will maintain between 100 and 125 pounds of pressure per square inch. While you are considering the pressure necessary for a job, there are a few acronyms with which you should be familiar. PSI is the measure of force the air will deliver to the tool. CFM is a volume measurement of cubic feet per minute, while SCFM is the standard cubic feet per minute. The relationship between the PSI and the CFM are key. Each tool you plan to use will have a requirement of both PSI and SCFM. For example, a paint sprayer may require just 40psi and 2scfm while a sander may require 90psi and 7 or 8scfm (or more) to operate at peak. Another consideration is the size of the tank. The larger the tank, the less the unit will need to run to keep up with the air flow requirement. For example, if you are trying to run a tool that has a high volume requirement (like a grinder) on a small 2-4 gallon tank, then the unit will be running very often or even continually. This could lead to a shortened lifespan of your unit. This really is a factor if you are planning to run sanders, grinders, or other high volume tools. For the typical user and typical applications, there should be no issues with going for a more compact, portable unit. Take the time to try to envision all of the things you may use your compressor for, so you can purchase the unit that will best fit your needs, while still letting you balance your budget!
A manual thermal overload button is another good feature for your air compressor to have. When a compressor engine overheats, it will shut down automatically. The thermal overload button must be pressed for the compressor to start up again after the engine has cooled. The button is meant to prevent sudden or unexpected motor start ups.
A belt guard is a necessary component for any air compressor. If your compressor does not have a belt guard, do not start it!
Now that you have found the perfect air compressor with all the needed accessories, it is time to get it working. Start by checking the oil level to ensure the compressor is properly lubricated if it is an oil-based unit. Next, plug it into a grounded three-pronged outlet. Close the tank drain valve and turn on the pressure switch. Adjust the pressure to the specific tool you will be using. It is vital you do not exceed the recommended pressure. When you are finished with the job, shut off the motor, unplug the unit and turn off the regulator valve. Slowly remove any extra air in the tank through the hose. If you have a quick connect, you can use the hose or you can use the drain cocks. After you are finished with the hose and it is properly stored, open the drain cock to release any accumulated moisture. Leave the drain cock open until the next time you use the compressor. If you will be using your unit for extended periods, and choose not to take the steps mentioned above, please be aware that the tank should be drained of the natural moisture that will build up daily. This is to prevent rusting the tank out.
If you ever think of purchasing a used compressor, inspect it closely for damage to the tank. Defective motors and pumps can often be replaced, but a damaged tank could spell real trouble and expenses for you. Also, NEVER attempt to repair a defective tank by welding or otherwise trying to seal a leak. It can lead to serious injury or death!
Above all, it is important to read the manufacturer’s instructions. At some point you will require air compressor repair service. If you do not follow the manufacturer’s instructions, it is likely that equipment repair will not be covered by the warranty. Closely read the warranty and make sure you do not void it in any way.