Best Air Compressor Buying Guide
What is Air Compressor?
Air Compressor is a device which converts power into potential energy stored in pressurized air. In easier team it is a pneumatic device which uses high pressure air to utilize in different tools. There are several methods by which, an air is compress and forced into storage tank by increasing the pressure. This compressed air is then used in variety of task and pneumatic devices.
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How Air Compressors Function
There are different types of air compressors available in the market. Air compressor capacity depends of the type and size of compressor. There are single-stage and double-stage compressor depending on the piston type.
Single-stage, piston-type air compressors are the most common models for home use and work. Piston gets drive from an electric motor or gasoline engine, which forces air into a storage tank. As the piston forces more air in different stages, the air pressure rises. Once the pressure reaches a specified level, the compressor stops running. This stores the compress air in the storage tank which can be used later for any job.
Two-stage, piston-type air 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, and are used in commercial models that can deliver a greater volume of air at higher pounds per square inch (PSI) levels.
Types of Air Compressors
There are three basic types of air compressors
- Reciprocating air compressors
- Rotary Screw air compressors
- Rotary Centrifugal air compressors
These types are further specified by:
- the number of compression stages
- cooling method (air, water, oil)
- drive method (motor, engine, steam, other)
- lubrication (oil, Oil-Free where Oil Free means no lubricating oil contacts the compressed air)
- packaged or custom-built
Reciprocating Air Compressors
Reciprocating air compressors are positive displacement machines, meaning that they increase the pressure of the air by reducing its volume. This means they are taking in successive volumes of air which is confined within a closed space and elevating this air to a higher pressure. The reciprocating air compressor accomplishes this by a piston within a cylinder as the compressing and displacing element.
Single-stage and two-stage reciprocating compressors are commercially available.
Single-stage compressors are generally used for pressures in the range of 70 psig to 100 psig.
Two-stage compressors are generally used for higher pressures in the range of 100 psig to 250 psig
Rotary Screw Compressors
Rotary air compressors are positive displacement compressors. The most common rotary air compressor is the single stage helical or spiral lobe oil flooded screw air compressor. These compressors consist of two rotors within a casing where the rotors compress the air internally. There are no valves. These units are basically oil cooled (with air cooled or water cooled oil coolers) where the oil seals the internal clearances.
Since the cooling takes place right inside the compressor, the working parts never experience extreme operating temperatures. The rotary compressor, therefore, is a continuous duty, air cooled or water cooled compressor package.
Rotary screw air compressors are easy to maintain and operate. Capacity control for these compressors is accomplished by variable speed and variable compressor displacement. For the latter control technique, a slide valve is positioned in the casing. As the compressor capacity is reduced, the slide valve opens, bypassing a portion of the compressed air back to the suction. Advantages of the rotary screw compressor include smooth, pulse-free air output in a compact size with high output volume over a long life.
The centrifugal air compressor is a dynamic compressor which depends on transfer of energy from a rotating impeller to the air.
Centrifugal compressors produce high-pressure discharge by converting angular momentum imparted by the rotating impeller (dynamic displacement). In order to do this efficiently, centrifugal compressors rotate at higher speeds than the other types of compressors. These types of compressors are also designed for higher capacity because flow through the compressor is continuous.
Adjusting the inlet guide vanes is the most common method to control capacity of a centrifugal compressor. By closing the guide vanes, volumetric flows and capacity are reduced.
The centrifugal air compressor is an oil free compressor by design. The oil lubricated running gear is separated from the air by shaft seals and atmospheric vents.
Air Compressor Power Source
There are two main power sources for Air compressors; either they are power by electricity or gasoline.
Electric compressors are the most widely used which are generally run on standard household voltage, between 110–120V. Compressors with motors that exceed two running horsepower require a 220–240V outlet. Since electric compressors don’t emit fumes, they are the better choice for indoor applications.
Gasoline or gas-powered compressors are generally used by builders and re-modelers because of their high output and convenience at the job-site. However, these compressors emit exhaust and should only be operated outdoors or in well-ventilated work areas.
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
- Air hammers / chisels
- Paint sprayers
- Rotary tools / grinders
Air Compressor Features
- Understanding available air compressor features helps you choose a model that can handle your Air-Cooling System: Cools pumping machinery to extend motor life
- Thermal Overload Switch: Automatically shuts off motor if it overheats, increasing tool life and protecting your investments.
- ASME Certification: Indicates high-quality material and craftsmanship, identified on the tank with a certification label stating that the unit meets the standards of the American Society of Mechanical Engineers.
- Roll Cage: Protects the compressor from being crushed or battered on the job site.