How an Air Compressor Works
Single-stage, piston-type air compressors are the most common models for home use and work well for many applications. An electric motor or gasoline engine drives a piston, which compresses air and forces it into a storage tank. As the piston forces more air in, the air pressure rises. Once the pressure reaches a specified level, the compressor stops running. As you use the stored air to power a tool, the compressor restarts to build the air pressure back up.
Two-stage compressors have two pistons. The first compresses the air and pushes it through a check valve to the second piston, which compresses it further and delivers it to the tank. These compressors are usually heavy-duty, commercial models that can deliver a greater volume of air at higher pounds per square inch (PSI) levels. They're good choices for continuous use in shops or if you need to power multiple tools at once.
Types of Air Compressors
Stationary air compressors are large devices designed for placement in a shop or garage. These high-horsepower models with large storage tanks allow for longer periods of uninterrupted use. They typically have a vertical design that reduces the amount of floor space they require.
A portable air compressor is more compact than a stationary model. It has a smaller storage tank and handles or wheels that allow you to easily move it to different work areas. Portable air compressors are good for light, quick applications, such as airbrushing and powering most types of nail guns. They come in several styles so you can choose the best portable air compressor for you:
- Pancake compressors have round, flat storage tanks mounted on the bottom of the units. The design adds stability and takes up less space than other styles.
- Hot dog compressors have a horizontal design with a single, cylindrical tank.
- Twin-stack compressors have two horizontal, cylindrical tanks. The stacked design adds air capacity without increasing the floor space the unit needs.
- Wheelbarrow compressors have twin cylindrical tanks and feature a wheel and handles for easy mobility.
- Inflators are the smallest compressors. An inflator doesn't have a storage tank, so the motor must run continuously to supply air. This type of compressor can inflate small floats, tires and sports equipment.
Air Compressor Power Supply
Electric compressors are the most common type of air compressor. These require less maintenance than gasoline-powered models, are quieter and work in any dry area with a ready electrical supply. Electric compressors are suitable for working indoors. Many home-use compressors function on 120-volt household current, but larger models may have different requirements. A portable electric compressor requires a suitable extension cord, which limits mobility. Follow the manufacturer's specification for extension cords and see Power Cord Safety Tips. Depending on the model, inflators plug into a 120-volt household outlet or a 12-volt vehicle accessory outlet.
Gasoline-powered air compressors are a good choice for outdoor work areas where electricity is limited or unavailable. A gas air compressor typically has more horsepower than an electric model, so it can generate greater PSI.
Air Compressor Specifications
The horsepower (HP) rating for a compressor indicates the power output of the engine or motor. Higher horsepower creates greater air pressure, measured in PSI. Higher PSI means the compressor can store more air in the tank, allowing you to operate air tools longer. Cubic feet per minute (CFM) and standard cubic feet per minute (SCFM) describe the volume of air a compressor delivers at specific PSI levels. The CFM value changes as PSI changes. As you lower the PSI output, CFM increases. A compressor with a higher CFM rating can deliver more air and is better suited for heavier applications, such as operating air wrenches and framing nail guns.
Compressor manufacturers rate storage tank size in gallons. Smaller tanks — around 4 to 6 gallons — are sufficient for many projects, such as airbrushing and operating brad nailers or nail guns. Larger tanks store more compressed air at higher pressures. They're suited for larger tasks that require sustained air flow, such as automotive work and remodeling projects.
Air Compressors and Air Tools
Powering air tools is the key function for an air compressor. Consider the tools you want to use now and those you might need in the future. Examples include:
- Nail and staple guns
- Impact wrenches
- Ratchets
- Air hammers/chisels
- Paint sprayers
- Rotary tools/grinders
Most air tools have specific requirements for air volume and pressure. A compressor must meet these requirements for the tool to function properly. When choosing an air compressor, consider the tools you want it to power. Determine which one requires the highest CFM at the highest PSI. Add 50 percent to the required CFM for a margin of safety, and look for a compressor that meets the requirement. For example, if a tool requires 3 CFM at 90 PSI, select a compressor that delivers at least 4.5 CFM at 90 PSI.
Air Compressor Features
In order to choose the right model, you should understand the air compressor features that can handle your jobs and simplify your work:
- An oil-free pump reduces maintenance and doesn't mix oil into the compressed air.
- A belt-drive system provides quieter operation than a direct-drive system.
- Thermal protection stops the motor to prevent damage from overloads.
- Adjustable exhaust allows you to direct exhaust away from your work area.
- Multiple couplers allow you to handle different tasks, without connecting and disconnecting tools.
- Included accessories and tools — such as hoses, nailers and blow guns — add value to your investment. Not all compressors come with air hoses.
- You can purchase auxiliary air tanks to increase air storage capacity.
Air Compressor Parts
The right parts and accessories are crucial to completing your projects safely and efficiently. Some of the main types of air compressor parts include:
- Hose: The type of hose you need will depend on the kinds of job you're doing and the tools you're using. Framing, roofing, painting and other projects where you need to travel some distance from your compressor will require a long hose. The length and diameter of your hose determine how much air pressure the compressor can deliver to your tools. Air compressors are rated by how much air they can deliver per cubic feet per minute (CFM), so make sure to choose a smaller diameter hose for a low CFM compressor and a larger diameter for a high CFM compressor.
- Hose reel: An air compressor hose reel makes taking out and putting away your hose quick and easy.
- Coupler: Couplers are used to attach your hose to your compressor and different tools to your hose. Quick release couplers make it easy to switch between several different tools. Couplers for air compressors typically come in industrial and automotive styles for use with different tools.
- Gauge: A gauge allows you to monitor your compressor's air pressure.
If you just bought a new air compressor or you're in need of multiple parts, you can also look into accessory kits that are designed for a variety of tools or repairs.