Some of the important specifications to look at when buying an air compressor are the tank capacity and the air volume that can be pumped each minute. It is usually a good idea to find a used compressor that is rated 25-30% higher than your needs, because overworking these machines can lead to premature failure. A small tank will typically suffice for tools that use short bursts of air, while larger tanks are required for sustained use such as sanders and paint guns. There are also a number of unique concerns when looking for the best used compressor, most of which depend on whether the previous owner kept good maintenance records. Compressors can be either oil free or lubricated, and it is typically a good idea to choose a used model that can be lubricated, especially if you are provided with records of past maintenance.
Air compressors are machines that consist of two primary components, which are a pump and a storage chamber. The pump pulls in air and compresses it into the chamber, where it can be held until it is needed. This compressed air can then be used to power a variety of pneumatic tools, blow guns, and paint sprayers. Similar compressors are also used in refrigeration and other applications where they pump and compress substances other than air.
The first step in any search for an air compressor is to estimate how much capacity you require. This can be done by adding up the needs of all the tools you expect to use at once, and then including a little more a buffer. It is always a good idea to buy an air compressor that is slightly larger than you expect to need, but this can be especially important when purchasing a used compressor. If you buy a unit that barely meets your needs, the pump will have to work harder and longer, which can lead to premature failure. A general rule of thumb is to select a unit that is capable of putting out at least 25% more volume per minute than you expect to need.
After you have determined the best compressor size for your needs, another factor to consider is whether to go with a model that is oil free or lubricated. Oil free compressors require little or no maintenance, since they do not need to be lubricated regularly. Lubricated compressors do need regular maintenance, but if these units are taken care of, they can last much longer. If you can find a lubricated used compressor that has extensive maintenance paperwork, that will typically be the best choice. An oil free used compressor can be the better choice in some circumstances, especially if there are no maintenance records available, and the price is reaasonable.