What Is An Air Compressor? The Function Of Air Compressors

Air compressors are essential to the smooth operation of factories and workshops all over the world in the modern pneumatics world. They weren’t always that way, though. In the history of the machine age, air compressors are a relatively recent invention.

Prior to the invention of air compressors, numerous tools were powered by intricate systems that included belts, wheels, and other substantial parts. Typically out of reach for many small operations, this equipment was large, expensive, and heavy. These days, air compressors can be found in a wide variety of sizes and shapes in garages next to you as well as on large shop floors and in auto workshops. In this article, we’ll go over how air compressors operate, covering everything from their fundamental operation to the various ways that various compressors handle air displacement.

What Is An Air Compressor?

A pneumatic device known as an air compressor transforms power using an electric motor, a diesel engine, a gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). An air compressor raises the pressure in a storage tank by one of several methods by pushing more and more air into it. The air compressor switches off when the pressure in the tank reaches its designed upper limit.

So, the tank stores the compressed air until it is needed. Utilizing the kinetic energy of the air as it is released and the tank depressurizes, the compressed air’s energy can be used for a number of different applications.

When the tank pressure drops to its lowest point, the air compressor restarts and pressurizes the tank once more. Because it operates for any gas or air, an air compressor must be distinguished from a pump, which operates on a liquid.

How Air Compressors Function

From pumping air into a tire to running a nail gun, air compressors can power a variety of tasks. Find out where to look for a compressor that can handle your jobs.

The most popular models for home use are single-stage, piston-type air compressors, which are useful for a variety of tasks around the house or workshop. Driving a piston, which compresses air and propels it into a storage tank, is either an electric motor or a gasoline engine.

The air pressure increases as more air is pushed in by the piston. The compressor shuts off when a certain pressure is reached. The compressor restarts as you use the compressed air to power a tool in order to restore the air pressure.

Two pistons are present in two-stage compressors. The first piston compresses the air before sending it through a check valve to the second piston, who then further compresses it before sending it to the tank. Typically, these compressors are heavy-duty, commercial models that can deliver more air at higher PSI (pounds per square inch) pressures. They make excellent options for shops that run continuously or for simultaneously powering several tools.

The Function Of Air Compressors

Air compressors pressurize a container by forcing air into it. After that, the air is pushed through a tank opening under pressure. Imagine it as a balloon that is open. the compressed air can be used as energy as it’s released.

A motor inside them converts electrical energy into kinetic energy. A crankshaft, piston, valve, head, and connecting rod are used, which is similar to how a combustion engine operates.

From there, a variety of tools can be powered by the pressurized air. Nailers, impact wrenches, sanders, and paint sprayers are a few of the more well-liked choices.

There are various types of air compressors, and each one has a unique specialty. In general, the differences are not too pronounced: it all boils down to the way a compressor handles air displacement.

Air Compressor Power Supply

The most popular types of compressors are electric ones. They operate in any dry space with an available electrical supply, are quieter than models powered by gasoline, and require less maintenance. Electric compressors are suitable for use indoors.

Many compressors intended for domestic use run on 120-volt household current, but larger models might have different needs. Mobility is restricted by the need for an appropriate extension cord when using a portable electric compressor.

Inflators can be plugged into either a 12-volt or 120-volt household outlet, depending on the model. When working outside without access to electricity, gasoline-powered air compressors are a good option. They typically produce more PSI than electric models because they have more horsepower.

Air Compressors And Air Tools

An air compressor’s primary use is to power air tools. Think about the tools you want to use right now and those you might need later. Examples include:

• Nail and staple guns
• Impact wrenches
• Ratchets
• Air hammers/chisels
• Paint sprayers
• Rotary tools/grinders

The majority of air tools have particular air pressure and volume requirements. For the compressor to work properly, it must fulfill these specifications. Think about the tools you want the air compressor to power when choosing one.

Choose the one that requires the most CFM at the most PSI. Find a compressor that meets the requirement by adding 50% to the needed CFM as a safety margin. Select a compressor that delivers at least 4.5 CFM at 90 PSI, for instance, if a tool needs 3 CFM at that pressure.

Air Compressor Features

Understanding the air compressor features that can handle your jobs and make your work easier will help you choose the best model:

• A pump that doesn’t mix oil into compressed air reduces maintenance and is oil-free.
• A belt-drive system operates more quietly than a direct-drive system.
• To stop overload-caused damage, thermal protection shuts down the motor.
• You can direct exhaust away from your work area with adjustable exhaust.
• Without connecting and disengaging tools, you can manage different tasks with multiple couplers.
• Tools and accessories like hoses, nailers, and blow guns are already included, which increases the value of your purchase. Some compressors do not include air hoses.
• To increase your ability to store air, you can buy auxiliary air tanks.

Applications Of Air Compressors

Air compressors can be used for a variety of tasks, such as supplying high-pressure, clean air to fill gas cylinders, providing moderately pressure, clean air to a diver working below the surface, and providing moderately pressure, clean air to drive some pneumatic HVAC control valves in office and educational buildings.

producing large volumes of moderate-pressure air for large-scale industrial processes (such as oxidation for petroleum coking or cement plant bag house purge systems) and supplying a significant amount of high-pressure air to fuel HPA, tire inflation, pneumatic tools like jackhammers, and other pneumatic equipment.

The flushing medium, aerating muds in underbalanced drilling, and air pigging of pipelines are all common uses for air compressors in the oil and gas, mining, and drilling industries.

The three main types of air compressors are rotary vane, rotary screw, or reciprocating piston. Centrifugal compressors are frequently used in very large applications, while rotary screw, scroll, and reciprocating air compressors are preferred for small and medium-sized applications.

Why Does Air Displacement Happen?

Each air compressor operates on the principle of air displacement. Air is pushed through the chamber of the compressor by internal mechanisms, which move to compress the air. The two main kinds of air displacement employed for this purpose are:

Positive displacement The majority of air compressors operate in this way, drawing air into a chamber. There, the device reduces the chamber’s volume in order to compress the air. Following that, it is transferred to a storage tank and kept for later use.

Dynamic displacement: This technique, which is also known as nonpositive displacement, introduces air into the chamber using an impeller with rotating blades. Air pressure is created more quickly thanks to the energy generated by the blades’ motion. Because it operates quickly and produces large volumes of air, dynamic displacement can be used with turbocompressors. Air compressors with dynamic displacement are frequently used in car turbochargers.

Types Of Positive Displacement Air Compressors

There are many different positive displacement air compressors because this type of air compression technique is more prevalent. The way they all operate, though, varies. While some are better suited for industrial use, others are more appropriate for smaller applications and DIY projects. Here are a few examples of the various positive displacement air compressor types:

Rotary screw: A rotary screw compressor is common in industry and comes in sizes to suit a variety of applications. Inside the motor of these compressors are two continuously rotating screws that rotate in opposing directions. An air-sucking vacuum is produced by the turning of the screws. This air is forced between the threads of the screws, where it gets trapped and compressed. Finally, it is discharged into a containment tank or through the output. Although oil-free compressor designs are also available, industrial-sized rotary screw compressors are the most common and are lubricated with oil.

The operation of oil-injected rotary screw compressors is explained in more technical detail below:

1. At the inlet valve, atmospheric air enters the compressor.
2. The air pressure in the system is set as it passes from the regulator valve through the pressure control line.
3. Once inside the compressor, air and oil combine to form a mist.
4. As the two internal screws rotate counterclockwise, air moves along their entire length.
5. Air is trapped and compressed in the space between the screws as a result of the vacuum created by the screw motion.
6. Pressurized air is forced through the output and into the primary oil separator tank while still mixed with the oil as a mist.
7. The majority of oil molecules in the tank condense into droplets and gather at the bottom as reusable oil due to centrifugal force.
8. After that, more oil is removed from the air in a secondary separation filter, further cleaning it.
9. The oil-free air leaves the system and is either immediately put to use in a connected pneumatic tool or piece of equipment, or it is stored in a tank.

Rotary vane: The operation of a rotary screw and a rotary vane compressor or vacuum pump is similar. A motor is off-center within a rounded cavity when using a rotary vane. The engine has blades with automatically adjusting arms. The arms become longer as they get closer to the air input, making a big air cavity. The arms get smaller as they near the output and get smaller, which reduces the distance between the vanes and the round casing, compressing the air as the motor spins, carrying air with it. For contractors and homeowners, vane-operated rotors are a great choice because they are compact and simple to use.

Because rotary vane and rotary screw compressors are similar, the following is a technical explanation of the operation of a rotary vane air compressor for comparison:

1. The compressor is filled with atmospheric air that enters through the inlet valve.
2. On the internal rotating rotor, which is positioned asymmetrically inside the cavity, vanes are mounted.
3. The room is divided into several cavities of various sizes by self-adjusting arm lengths.
4. Following the rotor’s rotation, air fills the cavity and circulates inside it.
5. Air pressure increases and compresses the air as the cavity gets smaller.
6. After that, the compressor’s output is pushed with the pressurized air.

Reciprocating/piston: A rotor’s rotation causes a piston to move up and down in a reciprocating air compressor. Air that is not in a chamber is drawn into it when the piston descends. As the piston rises back up, the air is then compressed and pushed back outward. One piston is all that some compressors—referred to as single-stage compressors—use. Some can pressurize more air than others; these are known as two-stage compressors. They use two pistons. One of the most prevalent air compressor designs is reciprocating.

The Mechanics Of An Air Compressor

Depending on the design, air compressor operation may differ. Piston-based air compressors can have one of two types of compression cycles

Single-stage: In one stroke, the piston compresses the air. One complete crankshaft rotation propels the piston during one stroke. Numerous of these compressors are ideal for home projects due to their straightforward, single-stage construction.

The technical steps for a single-stage air compressor are as follows:

1. A single piston is made to rise and fall by the rotation of the rotor.
2. As soon as the piston descends, the valve opens, allowing atmospheric air to enter the compression chamber.
3. As the piston rises, the air is compressed as it is pushed into the output chamber.
4. The compressor’s output is then pushed with the pressurized air.

Two-stage: A second piston further compresses the air after the first has compressed it and moved it to a smaller cylinder. Because of this design, the compressor can produce higher pressures, which makes it perfect for factories and workshops. Many two-stage systems also cool air as it moves between each cylinder because the kinetic energy that compresses air produces heat. By cooling the air, the compressor can move more air without getting too hot.

A two-stage air compressor works as follows:

1. The rotor rotates to simultaneously control two pistons, causing each piston to move up and down in the opposite direction.
2. The larger piston forces air into the initial compression chamber before pushing it out to the intercooler.
3. The air is cooled by the intercooler using a steady stream of water.
4. By squeezing a lot of air into a small area, the smaller piston increases the air’s pressure.
5. Following that, the small piston pushes the pressurized air through the output.

A Reciprocating Piston Is What?

The reciprocating piston consists of the following components:

• Crankshaft
• Connecting rod
• Cylinder
• Piston
• Valve head

It functions similarly to a car’s internal combustion engine. The air volume is reduced and the pressure is increased as the crankshaft rod raises the piston in the cylinder and forces air into the compression chamber. When the piston closes, compressed air is forced into the storage tank. Once more drawing in air, the piston then depresses itself, beginning the cycle all over again.

Because of how the machine’s parts move and produce friction, piston-based compressors may be noisier than some other types. Dual and multi-piston models, which can reduce noise by dividing the workload, are now available thanks to new technologies and advanced designs.

The Rotary Screw Air Compressor

A piston compressor simply isn’t sufficient in many heavy-duty industrial applications. Professionals frequently select rotary screw air compressors to achieve the higher pressures required for complex pneumatic and high-powered tools.

A rotary screw compressor is continuous, as opposed to the pulsation and alternation of the piston mechanic used by a piston air compressor. The air is drawn in and compressed as it spirals through a pair of interlocking rotors. The air is ejected out of a chamber by the rotating motion. Leakage can be decreased with rapid rotational rates.

Many different types of compressors shake occasionally, which can harm the machinery and necessitates taking precautions to reduce vibrations. On the other hand, the majority of rotary screw compressors run quietly for consistent, vibration-free performance.

Rates for rotary screw compressors range from 10 CFM to those in the 4-5 figure range, with a wide range in between. Control strategies include:

• Stop/start: Depending on the application, this method either gives the motor power or doesn’t.
• Load/unload: The slide valve in the continuously running compressor lowers the tank’s capacity when a certain compression demand is met. It is referred to as a dual-control scheme if a stop timer is used, and it is frequently used in factory settings.
• Modulation: By throttling/closing the inlet valve and adjusting the sliding valve, modulation can also adjust pressure by balancing the capacity and demand of the compressor. Compared to other types of compressors, rotary screw compressors are less responsive to these adjustments. The compressor would still use about 70% of its total power load even when set to a 0 capacity. Modulation, however, is useful for operations where frequently stopping the compressor is not an option.
• Variable displacement The air volume that is drawn into the compressor is altered by this control system. This method can be used in conjunction with modulating inlet valves in rotary screw compressors to increase productivity and precision of pressure control.
• Variable speed: A rotary compressor’s capacity can be efficiently managed with variable speed, though different air compressor types may react differently to it. It alters the motor’s speed, which has an impact on the output. It may not be suitable for use in particularly hot or dusty work environments because this equipment is typically more delicate than other designs.

How Air Compressors Use Lubrication Oil-flooded Vs. Oil-free

Understanding how lubrication functions is among the most crucial aspects of air compressor maintenance. There are two types of oil pumps to consider:

• Oil-lubricated pumps: Oil splashes onto the cylinder’s walls and bearings in this design. This approach, which is also known as oil-flooded lubrication, has the advantage of being more robust. The metal piston ring, which is located on the piston and aids in sealing the combustion chamber, is a component. Although this ring can help, oil may occasionally still seep into the tank and into the compressed air.
• Oil-free pumps: Pumps designed to operate without oil are given a special, long-lasting lubrication. Breweries, food production, and pharmaceutical manufacturing are just a few of the sectors where oil-free pumps are a great choice because contamination is not an option. They take precautions to ensure that no oil contaminates the air they use to produce their process or product.

There are a variety of oil-flooded pumps. The presence of oil in the air stream can be helpful for power tools that require lubrication. Inline sources can disperse oil in precise amounts for tools that require it. However, if even trace amounts of oil are present in the air stream, many tools may cease to function properly.

Oil can completely halt the process of painting or woodworking. It might prevent coatings from finishing or drying properly. Even projects made of wood can develop surface damage from airborne oil.

Thankfully, devices like air-line filters and oil separators exist to stop oil from getting into the tank. Oil-free compressors and their permanent lubrication, however, are the best choice when oil-free air is essential to operation.

Ratings For Air Compressor Power: What Is Cfm?

There are many different ways to assess how much pressure a machine can produce. When discussing power in an air compressor, we frequently use the term horsepower, but there are many other options as well. The rate and volume by which an air compressor compresses air is measured in cubic feet per minute (CFM). However, the temperature, humidity, and wind in the surrounding atmosphere have an impact on the rate at which outside air enters the cylinder.

Manufacturers use standard cubic feet per minute (SCFM), which combines CFM with those external factors of pressure and humidity, to account for these internal and external factors.

Displacement CFM, which evaluates the effectiveness of the compressor pump, is a different rating you might encounter. It gathers data from the motor’s revolutions per minute (RPM) and the amount of air the cylinder can move. Although CFM can also be measured in terms of delivered air or how much is actually discharged, this figure is more of a theoretical measurement. CFM FAD, or free air delivery, is the abbreviation for this number, which is helpful for calculating delivery to particular tools.

Compressors Versus Pumps Two Instruments For Harnessing Air

The terms “pump” and “compressor” are sometimes used interchangeably, leading to some confusion. In actuality, making the distinction between the two is essential when talking about air compressors:

• Gases or liquids can be moved between locations with the help of a pump.
• A compressor takes a gas, increases its pressure and reduces its volume before sending it somewhere else.

A pump can operate with liquids, whereas a compressor cannot, and this is the most important distinction. Compressing liquids is much more challenging. A pump may be found inside a compressor, such as in a reciprocating air compressor, where the pump is the component that actually performs compression. On machines where the pressure increases with each revolution, the roles of pumps and compressors may overlap.

For instance, consider a tire pump. While it does both of these things—moves air and decreases its volume—its primary function is to move outside air into the airtight space of the tire. It’s not technically a compressor because its aim isn’t to lower the volume. Using pneumatic tools, which require compressed air, would serve as a different illustration. A compressor is the mechanism that lowers the volume of air.

Typically, there are two types of air pumps:

• Pumps that reciprocate back and forth. A bicycle pump is a reciprocating pump that forces air into the tire by pulling air from the outside in a back-and-forth motion.
• Centrifugal pumps, also known as rotary pumps, rotate. An impeller, which is essentially a sealed propeller, is used in rotary pumps. It has blades that swiftly and efficiently channel incoming fluid through an outlet. Contrary to a turbine, which collects moving fluids, this pump uses motorized energy to move fluids from one location to another.

Compressed Air In Everyday Life

A wide variety of air-powered tools and machines, such as pneumatic drills, braking systems, and HVAC units, improve the comfort, safety, and effectiveness of daily life. A person used air tools to sand the wood, paint the walls, and hammer beams and plasterboards into place in almost every building you walk through or pass by on any given day. People use compressed air to add paint coats and blast debris and dust off of shop floors all over the world.

It is nothing short of amazing that humans have been able to use ambient air, which is possibly the most plentiful resource on the planet, to power motorized machinery for a variety of uses.

High-quality air compressors in a variety of designs, such as rotary screw, reciprocating/piston, and oil-free, are available from Quincy Compressor. To find a dealer close to you, use our sales and service locator.