Anyone who uses any sort of air tools, from air nailers to impact wrenches, needs a compressor to power them. What type of compressor and how big a compressor are questions that may be hard to answer. Nevertheless, they have to be answered in order to pick out the best possible compressor for your needs.
While there are many ways of compressing air, the standard way used for air compressors is via a piston. The piston works much like the piston on an engine, packing the air into about 1/8 of its original volume. This compressed air then leaves the piston and is stored in a tank. By using a tank, the compressor is able to supply bursts of air which are a much higher volume than the compressor can produce.
Air compressors are typically designed to compress the air to 120 PSI, the maximum most air tools are designed to handle. However, air tools are typically rated for operation at 90 PSI, so you’ll see many air compressor specifications listed at this pressure. Manufacturers usually list specs for two pressures, 30 PSI and 90 PSI respectively.
Air Compressor Types
Due to the high number of different air compressor models available, there are actually many different ways of categorizing air compressors,. Air compressors are used in home workshops, woodworking shops, and mechanics shops, as well as extensively in heavy industry as well. For the purpose of this buyer's guide, we are concentrating primarily on air compressors that would be used by a do-it-yourselfer or a contractor, not industrial-model compressors.
There are three basic categories of compressors to choose from, with several different styles within each of these categories which include the following:
Portable
Meant to be carried. These compact compressors are used where not a lot of air volume is needed, mostly by finish carpenters for their air nailers.
Contractor
The “mid-range” compressor, used by everyone from building contractors to do-it-yourselfers. These are wheel mounted so that they can be brought to the place where they are needed.
Shop
Shop air compressors are fixed location compressors which are used to provide air to several people working in the same shop. They are large units, which can provide a large quantity of air and have larger tanks.
Contractor compressors traditionally have a horizontally mounted tank and shop compressors typically have a vertically mounted tank. This allows a smaller footprint for the shop air compressor. Recently, manufacturers have started making contractor compressors with vertically mounted tanks as well, specifically so that they will take up less room in a workshop.
Other Types of Compressors
Although we don't list them, because they are designed for industry, there are a couple of categories of compressors that you should be aware of, just so that you will recognize them if you see them.
Gasoline Powered Air Compressors
Contractors working on a construction site may need to use an air compressor where there is no electrical power. Their options are to bring along an electrical generator or to use a gas powered air compressor. There are also diesel powered compressors, which are essentially the same, but designed so that they can be installed on a vehicle that uses diesel fuel instead of one that burns gasoline. Either type of gas powered compressor is much more expensive than an electrically driven one.
Multi-Stage Compressors
Multi-stage air compressors are used in industrial facilities where a large volume of high pressure air is needed. These are very large compressors that compress the air in stages, allowing them to produce a much higher final air pressure. Typically, the air pressure is regulated downward for use in tools.
Important Air Compressor Specifications
Cubic Feet Per Minute (CFM)
Most manufacturers tout the horsepower rating of their compressors, but that’s really not the important specification. The important one is the amount of air that the compressor can continually supply, measured in cubic feet per minute (CFM). The CFM of the compressor has to be higher than any of the tools which are connected to it. If not, the compressor won’t be able to keep up and the tool will slow down, losing power as well.
Shop compressors have a higher CFM rating and are normally intended for several air tools to be connected to them at the same time. In such a case it is necessary that the rating of the compressor be higher than the total of the average air usage of the tools.
Duty Cycle
By average air usage, I'm referring to the duty cycle. If you connect ten tools with the same air volume requirements to an air compressor, but each is only used ten percent of the time, it's the same as only having one tool attached to the compressor. So, you must consider duty cycle when you are determining the total volume of air required for these larger compressors.
Unless a compressor manufacturer specifically states that their product is designed for a 100 percent duty cycle, you can assume that it is designed for a 60 percent duty cycle. That means that the compressor’s motor shouldn’t be running for more than 60 percent of the time. If it does, the unit will produce more heat than it can dissipate, causing damage to the compressor.
Tank Size
Tank size is important in that the compressed air in the tank is the reserve you have. Your tools will draw air from the tank, which will then be replenished by the compressor. A pressure switch turns on the compressor motor when the air pressure in the tank drops to 95 PSI.
Horsepower/Maximum Pressure
Horsepower and maximum pressure are normally stated for compressors, but are not important specifications. The manufacturer will select a horsepower rating that is high enough to drive the compressor. The main reason that the horsepower rating is given is to impress potential customers.
Compressor Configurations
Any air compressor consists of the compressor itself, a motor to drive the compressor and an air tank. How the air compressor and the tank are physically connected together is not as important as that they are. However, through the years, a number of different styles have been developed, giving more variety to the number of compressor models on the market. Some configurations are easier to work with in certain situations than others.
Pancake
Pancake compressors are small, portable compressors, with six gallon tanks. The name comes from the basic shape of the tank. The compressor is mounted above the tank, making a compact unit.
Hot Dog
Hot dog compressors are another type of portable compressor. They use two small horizontal tanks, stacked. The compressor is usually a small one and sits on top of the tanks. These are about the only compressors which are likely to have a control panel.
Wheelbarrow
Wheelbarrow compressors are contractor compressors with two thin horizontal tanks. The name comes from the singe wheel which is mounted at one end, between the tanks. Twin handles are attached to the other end. This makes moving the compressor much like moving a wheelbarrow. The low profile of these compressors makes them ideal for loading in the back of a pickup truck with a bed cover.
Horizontal
The horizontal compressor is the standard contractor air compressor configuration, with a large horizontal tank and the compressor mounted above the tank. They tend to be unstable and tip over easily.
Vertical
Shop compressors are usually vertical compressors, with a large vertical tank and the compressor mounted above it. This allows for a larger tank, reducing the duty cycle of the motor. Some smaller vertical compressors have wheels, allowing them to be moved like a hand truck.