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 An air compressor is a device that takes in atmospheric air at normal pressure and emits the same at a much higher pressure after compression. This device comes in varied sizes and power ranges. Smaller air compressors have applications in tools for users at home or in small workshops and factories, while larger compressors may be used for heavy industrial applications. Air compressors are the source of power for pneumatic tools, such as nail guns, grinders, staplers, or air ratchets, provide the propelling force to either eject the nails out at high speeds or provide the vibrating impact action for the hammer and rivet tips. In an automobile workshop, air compressors are using to fill air bags placed below vehicles to elevate them during repairs as well as to fill pneumatic tires. Some of the smaller industries using air compressors include baking, dairy, food processing, metal plating and coating, heat treatment, plastics manufacturing, packaging, and printing. Spray painting, polishing, and application of protective coatings are some of the common household applications of air compressors.
Features and working of air compressor
An Air compressor uses different techniques to compress air and also come in different sizes and types depending on the intended use as well as on the industry. The most common compression mode used is to progressively decrease the original volume of the space occupied by the air within the device. The amount of compression the air is subjected to is measured in pounds per Square inch (PSI), and the efficiency of the compressor is measured by the cubic feet per minute (CFM) of air released per horsepower. Broadly, compressors are of two types; single stage compressors and multi-stage compressors. While single stage compressors are suitable for smaller jobs, two-stage or higher compressors are suitable for heavy-duty applications. A single stage compressor offers a maximum of around 125 PSI and a two-stage compressor generates a maximum pressure of approximately 200 PSI. Some specialized compressors offer up to 400 PSI.
The horsepower of a compressor is directly proportional to the CFM value, which stands for Cubic Feet per Minute, or the amount of air the compressor can deliver. Most Nailers, and staplers do not require a large CFM to operate, while other tools like air grinders require a high CFM. The CFM value is always somewhat lower than the actual compression of the air. Thus, the CFM value is a truer depiction of the performance of the compressor as compared to the PSI value. A good air compressor has a CFM value of around 45. Normally used compressors offer  horsepower values ranging from around 0.5 HP to around 30 HP.
All compressors have an air tank that serves as a reservoir for the pressurized air. These air tanks maintain a smooth flow of the air, avoiding any sudden spurts in the emission of air and also act as a storage facility when the demand for the air exceeds the supply. The capacities of these tanks are measured in liquid gallons. A bigger tank has more reserve pressurized air to meet with occasional greater demands, while a smaller tank will require the pump to work more vigorously during high volume compressor operations. All tanks should preferably meet the quality standards laid down by the American Society for Mechanical Engineers (ASME). Often, tanks have a built-in manually operated drain valve to ease excess pressure. Solenoid operated or float type automatic valves prevent damage due to non-drainage for a long period of time. The tank capacities range from around 2 gallons to more than 120 gallons.
One of the most important components of the processor is the pump, which is mostly made of either cast-iron or aluminum. Aluminum pump compressors are usually cheaper, but may not be durable in the long run. Additionally, the fewer number of individual moving parts the pump has, the better is its performance.
Compressors can be powered either by gas or by electricity. Electrical air compressors are more convenient as they can be plugged into a wall socket and used. Additionally, there are no gas fumes emitted from the device. Electrical compressors are often seen in air tools used for jobs such as farming, roofing and other general indoor-based applications. Gas powered air compressors are suitable for outdoor work where access to an electricity source is not available.
What to look for in a compressor
 With numerous moving parts in the device, the noise Levels are an important parameter of consideration. Most manufacturers have consciously designed the compressor to minimize noise levels. A roll-cage construction will enable the body of the compressor to withstand shocks and rough usage. A lower amp draw can avoid the incidence of tripped breakers or sudden voltage fluctuations that may damage the motor. An oil lubricated pump prevents wear and tear due to friction.
The size of the air compressor chosen should strike a balance between operational requirements and budgetary constraints. A small compressor may not provide sufficient air flow and force, while a compressor that is excessively large may consume more power and result in greater operating costs. The user also has the option to between a vertical air tank and a horizontal one. A vertical air tank is applicable for compressors using up to 10 HP, while horizontal tanks are applicable for compressors between 3 and 30 HP. Another function to be incorporated in a compressor is the option to choose the constant speed operation mode as opposed to the auto start / stop mode. This comes into play when the compressor is normally restarted more than 6 to 8 times per hour. Generally, the compressor should use only dry, clean air for maximum efficiency and longer life. Popular manufacturers of compressors include Chicago Pneumatic, Porter Cable, Coleman Powermate, Dewalt, Makita and Stanley-Bostitch.
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Air Tool CFM Requirements
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Air Tool Description
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Average CFM @ 90 PSI
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Angle Disc Grinder - 7"
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5-8
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Brad Nailer
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0.3
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Chisel/Hammer
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3-11
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Cut-Off Tool
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4-10
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drill, Reversible or Straight-Line
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3-6
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Dual Sander
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11-13
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Framing Nailer
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2.2
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Grease Gun
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4
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Hydraulic riveter
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4
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Impact Wrench - 3/8"
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2.5-3.5
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Impact Wrench - 1/2"
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4-5
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Impact Wrench - 1"
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10
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Mini Die Grinder
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4-6
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Needle Scaler
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8-16
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Nibbler
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4
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Orbital Sander
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6-9
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Ratchet - 1/4"
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2.5-3.5
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Ratchet - 3/8"
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4.5-5
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Rotational Sander
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8-12.5
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Shears
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8-16
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Speed Saw
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5
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Features to consider when purchasing an Air Compressor
- ASME (American Society of Mechanical Engineers) tank
- Belt-driven Air Compressor — Belt-driven compressors generally have a longer life, with less vibration and heat transferring from the motor/engine to the pump.
- Cast iron cylinder or cast iron pump sleeves — Cast iron is typically the standard material for cylinders
- Fully packaged unit with premounted and prewired magnetic motor start, dual control, belt guard mounted air cooled after cooler and electric condensate drain
- Low-oil shutdown prevents downtime and costly repairs resulting from low oil levels
- Oil-Free (or Oil-less) compressors are virtually maintenance-free performers for light- to general-duty applications. No need for periodic oil changes.
- V-design cylinders — V-design cylinders typically run cooler that in-line cylinders. Heat is a compressors worst enemy.
- Vertical vs. horizontal air compressors — Vertical compressors usually take up less floor space than horizontal compressors. Typically, vertical compressors are stationary, whereas smaller horizontal compressors are better for portable applications (such as a truck-mounted compressor).
- 100% Continuous Speed operation vs. Auto Start/Stop operation — Auto start/stop operation has preset cut in/cut out pressures. The compressor actually stops and turns back on as air is needed. With constant speed operation, the compressor runs 100% of the time and simply adjusts the air output. Dual control compressors offer both auto start/stop and continuos speed operation.
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