How Does industrial air compressor manual Work?

In the modern world of pneumatics, air compressors are vital to the operations of factories and workshops across the globe. But they haven&#;t always been. Air compressors are a relatively recent invention in the context of machine-age history.

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Before air compressors, many tools got their power from complicated systems with belts, wheels and other large components. This machinery was massive, heavy and costly, and typically out of reach for many small operations. Today, air compressors come in many shapes and sizes, and you can find them in large shop floors, auto workshops and even your neighbor&#;s garage. In this guide, we&#;ll discuss how air compressors work &#; from their basic functionality to the various ways different compressors handle air displacement.

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How Does an Air Compressor Work?

Air compressors work by forcing atmospheric air under pressure to create potential energy that can be stored in a tank for later use. Just like an open balloon, the pressure builds up when the compressed air is deliberately released, converting the potential energy into usable kinetic energy. From there, this energy transfer can be harnessed to power various pneumatic tools.

Industrial air compressors work similarly to combustion engines. Generally, air compressor operation requires a pump cylinder, piston and crankshaft to transfer energy for a wide variety of tasks. These basic components can help supply air for filling up objects like tires or inflatable pool toys, or they can supply power for operating tools such as drills, nail guns, grinders, sanders and spray guns.

From impact wrenches to AC units, many versatile air-powered tools and machines are responsible for the comfort, shelter, automation and efficiency of everyday life. The compressors themselves are more compact and lightweight than other centralized power sources. They are also long-lasting, require less maintenance and are easier to move than other old-fashioned machinery.

Piston Air Compressor Functionality

So, how does an air compressor get air? For those that use pistons, it involves two parts: Raising the pressure and reducing the volume of the air. Most compressors use reciprocating piston technology.

An air compressor typically uses:

• An electric or gas motor
• An inlet and a discharge valve to draw in and release air
• A pump to compress the air
• A storage tank

The compressor draws in air and creates a vacuum to reduce its volume. The vacuum pushes the air out of the chamber and into its storage tank. Once the storage tank reaches its maximum air pressure, the compressor turns off. This process is called the duty cycle. The compressor will turn back on when the pressure drops below a specific number.

Air compressors don&#;t need to have storage tanks, and a few of the smaller options forego them in favor of portability.

What Is Air Displacement?

Air displacement is at the core of each air compressor. To compress air, the internal mechanisms within the compressor move to push air through the chamber. There are two primary types of air displacement used for this purpose:

Positive displacement: Most air compressors use this method, in which air is pulled into a chamber. There, the machine reduces the volume of the chamber to compress the air. Next, it is moved into a storage tank and saved for later use.

Dynamic displacement: Also called nonpositive displacement, this method uses an impeller with rotating blades to bring air into the chamber. The energy created from the motion of the blades builds up air pressure in a shorter amount of time. Dynamic displacement can be used with turbocompressors because it works quickly and generates large volumes of air. Turbochargers in cars often use dynamic displacement air compressors.

Types of Positive Displacement Air Compressors

Because positive displacement is the more common type of air compression method, there is a large variety of positive displacement air compressors. However, each one works differently. Some are better for industrial use, and others are suitable for home projects and smaller applications. Here are some of the different types of positive displacement air compressors:

Rotary screw: A rotary screw compressor is typical for industrial use and has sizes to fit many applications. These compressors have two screws inside the motor, turning continuously in opposite directions. The motion of the screws creates a vacuum that sucks in air. That air becomes trapped between the screws&#; threads and is compressed as it is forced between them. Finally, it is sent through the output or into a containment tank. Most rotary screw compressors are industrial-sized and lubricated with oil, though oil-free compressor designs are also available.

Here&#;s a more technical look at how oil-injected rotary screw compressors work:

1. Atmospheric air enters the compressor at the inlet valve.
2. The air travels through the pressure control line to the regulator valve, a process that sets the system&#;s air pressure.
3. Air then enters the compressor, where it combines with oil into a mist.
4. Air travels the length of the two internal screws as they rotate in opposite directions.
5. The screw motion creates a vacuum, trapping and compressing air in the space between the screws.
6. The pressurized air is forced through the output and into the primary oil separator tank while still combined with the oil as a mist.
7. The centrifugal force inside the tank causes most oil molecules to form into droplets and collect at the bottom as reusable oil.
8. Air then enters a secondary separation filter where more oil is removed, purifying the air further.
9. The oil-free air exits the system, where it is stored in a tank or used immediately in a connected pneumatic tool or machinery.

Rotary vane: A rotary vane compressor or vacuum pump has a similar principle to a rotary screw. With a rotary vane, a motor is placed off-center inside a rounded cavity. The engine has blades with automatically adjusting arms. As the arms approach the air input, they are elongated, creating a large air cavity. As the motor spins, moving air with it, the arms approach the output and get smaller, creating a smaller space between the vanes and the round casing, which compresses the air. Vane-operated rotors are small and easy to use, making them great for homeowners and contractors.

Because of the similarity between rotary vane and rotary screw compressors, here&#;s a technical description of how a rotary vane air compressor functions for comparison:

1. Atmospheric air enters through the inlet valve and travels into the compressor.
2. Vanes are mounted on the internal spinning rotor, which is placed off-center inside the cavity.
3. Arms with self-adjusting length divide the space, creating several cavities of varying size.
4. Air fills the cavity and travels around, following the rotor&#;s rotation.
5. As the cavity gets smaller, air pressure builds up and compresses the air.
6. The pressurized air is then forced through the compressor&#;s output.

Reciprocating/piston: In a reciprocating air compressor, a rotor&#;s spin forces a piston to move up and down. When the piston goes down, freestanding air is pulled into a chamber. Then, the air is compressed and forced back outward as the piston rises back up. Some compressors, called single-stage compressors, use only one piston. Others, called two-stage compressors, use two pistons and are able to pressurize more air. The reciprocating type of air compressor is one of the most common.

The Mechanics of an Air Compressor

How air compressors work can vary according to design. Piston-based air compressors can have one of two types of compression cycles:

Single-stage: The piston compresses the air in one stroke. A stroke is one full rotation of the crankshaft driving the piston. The simple, single-stage design makes many of these compressors ideal for private projects.

Here are the technical steps of single-stage air compressor operation:

1. The rotor&#;s spin forces a single piston to move up and down.
2. When the piston moves down, atmospheric air is pulled into the compression chamber through the opened valve.
3. When the piston moves up, the air is compressed as it&#;s pushed into the output chamber.
4. The pressurized air is then forced through the compressor&#;s output.

Two-stage: The first piston compresses the air before moving it to a smaller cylinder, where another piston compresses it further. This design allows the compressor to generate higher pressures, making it ideal for factories and workshops. Since the kinetic energy that compresses air generates heat, many two-stage systems also cool air as it travels between each cylinder. Cooling the air allows the compressor to move more air without overheating.

Here&#;s how a two-stage air compressor operates:

1. The rotor spins to control two pistons simultaneously, forcing each piston to move conversely up and down.
2. The larger piston pulls air into the first compression chamber, then pushes it out to the intercooler.
3. The intercooler uses a continuous stream of water to cool the air.
4. The smaller piston compresses a large volume of air into a compact space, further pressurizing it.
5. The pressurized air is then forced through the output by the small piston.

How Does an Air Compressor Regulator Work?

A regulator attaches to the outlet for your compressor&#;s air tank and features an adjustable nob and a pressure indicator. As you rotate the knob counterclockwise, it pushes on a spring which restricts a valve, which lowers the pressure by reducing the supply of air entering the regulator. When you turn the knob clockwise, the spring and the valve release, allowing more high-pressure air through the output.

For many single-stage air compressors, the preset pressure limit is 125 psi. When this limit is reached, a pressure switch goes off to stop the motor and the production of compressed air. In most operations, you don&#;t need to reach that pressure limit, so many compressors set air lines to a regulator. With a regulator, you can input the appropriate pressure level for a given tool.

When the amount of pressure needed to power your tool is lower than the pressure in your air pressure tank, a regulator adjusts the pressure for you. While the regulator can&#;t raise the pressure above what&#;s already in your tank, it ensures your tool gets a consistent flow of air at the correct pressure.

When the specified pressure is reached, the regulator shuts off the pump at any point in its cycle, which means the piston can be halfway through a stroke, with pressurized air in the chamber, when it stops. This air can put undue pressure on the starting circuit, which needs more power to start the motor. An unloader valve is a simple addition that releases the trapped air to avoid this problem.

A regulator is bookended by two gauges &#; one to monitor the pressure of the tank and another to monitor the pressure within the air line. Also, the tank has an emergency valve that triggers if the pressure switch malfunctions.

What Is a Reciprocating Piston?

The reciprocating piston involves the following parts:

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

It works similarly to a combustion engine in a car. The crankshaft rod raises the piston in the cylinder and pushes air into the compression chamber, decreasing air volume and increasing the pressure. The piston closes, forcing the compressed air into the storage tank. Then the piston opens again to draw in more air and start the process over.

Compressors that use pistons can be louder than some other designs because of how the machine&#;s components move and generate friction. But new technologies and advancing designs are bringing dual and multi-piston models that can make things quieter by splitting up the workload.

The Rotary Screw Air Compressor

In many heavy-duty industrial applications, a piston compressor just doesn&#;t cut it. For the higher pressures needed for complex pneumatic and high-powered tools, professionals tend to choose rotary screw air compressors.

While the piston air compressor uses pulsation and the alternating nature of the piston mechanic, a rotary screw compressor is continuous. A pair of rotors mesh together to pull air in and compress it as it moves through a spiral. The rotary motion moves the air through a chamber and ejects it. Fast rotational rates can minimize leakage.

Many compressor types experience some shaking, which can damage the equipment and requires you to take measure s to minimize vibrations. In contrast, most rotary screw compressors operate smoothly for even, vibration-free performance.

Rotary screw compressors can vary widely, with rates from 10 CFM to those in the 4-5 figure range. Control schemes include:

• Stop/start: This approach either provides power to the motor, or it does not, according to the application.
• Load/unload: The compressor is powered continuously, with a slide valve that reduces the tank&#;s capacity when a specific compression demand is met. This scheme is common in factory environments, and if it involves a stop timer, it is called a dual-control scheme.
• Modulation: Modulation also uses a sliding valve to adjust pressure by throttling/closing the inlet valve, matching the compressor&#;s capacity to the demand. These adjustments are less effective on rotary screw compressors than other types. Even when set to a 0 capacity, the compressor would still consume about 70 percent of its full power load. Still, modulation is applicable for operations in which frequently stopping the compressor is not an option.
• Variable displacement: This control scheme adjusts the volume of air that is pulled into the compressor. In rotary screw compressors, this method may be used alongside modulating inlet valves to improve efficiency and pressure control accuracy.
• Variable speed: Variable speed is an efficient way to control a rotary compressor&#;s capacity, though it may respond differently with different types of air compressors. It varies the speed of the motor, which affects the output. This equipment tends to be more delicate than other designs, so it may not suit particularly hot or dusty work environments.

How Lubrication Works in Air Compressors: Oil-Flooded vs. Oil-Free

One of the most important things to know about air compressor maintenance is how lubrication works. When you&#;re looking at oil pumps, you&#;re dealing with two categories:

• Oil-lubricated pumps: In this design, oil splashes onto walls and bearings within the cylinder. This method is also called oil-flooded lubrication and tends to be more durable. A piston ring is a piece of metal on the piston that helps to create the seal inside the combustion chamber. This ring can help keep oil out of the compressed air, but sometimes it can still seep into the tank.
• Oil-free pumps: Oil-free pumps receive special lasting lubrication that eliminates the need for oil. Oil-free pumps are an excellent option in many industries where contamination is not an option, like breweries, food production and pharmaceutical manufacturing. They ensure that no oil contaminates the air they use in their process or product.

Oil-flooded pumps are somewhat of a mixed bag. For power tools that need lubrication, the presence of oil in the air stream can be beneficial. For tools that need oil, inline sources can distribute oil in even amounts. On the other hand, many tools can stop working correctly when even minute amounts of oil are present in the air stream.

For painting or woodworking, oil can interrupt the entire process. It may keep coatings from drying or finishing evenly. Airborne oil can even corrupt the surface of wood projects.

Thankfully, there are tools to prevent oil from entering the tank, like air-line filters and oil separators. Still, when oil-free air is critical to operation, oil-free compressors and their permanent lubrication is the best option.

Air Compressor Power Ratings: What Is CFM?

When we talk about power in an air compressor, we usually speak in terms of horsepower, but there are many other ways to determine how much pressure a machine can provide. We use cubic feet per minute (CFM) to discuss the rate and volume by which a machine compresses the air. But the rate at which outside air enters the cylinder is influenced by heat, humidity and wind in the surrounding atmosphere.

To consider these internal and external factors, manufacturers use standard cubic feet per minute (SCFM), which combines CFM with those outside factors of pressure and humidity.

Another rating that you might see is displacement CFM, which looks at the efficiency of the compressor pump. It pulls information from the revolutions per minute (RPM) of the motor and the volume of air that the cylinder can displace. This number is more of a theoretical measurement, while you can also measure CFM in terms of delivered air, or how much is actually discharged. This number is called CFM FAD, which stands for free air delivery, and is useful for measuring delivery to certain tools.

Pumps vs. Compressors: Two Instruments for Harnessing Air

Some degree of confusion exists between the words &#;pump&#; and &#;compressor,&#; with many believing them to be the same thing. In reality, the distinction between the two is a crucial part of discussing air compressors:

• A pump takes liquids or gasses and moves them between places.
• A compressor takes a gas, squeezes it down to a smaller volume and higher pressure and sends it elsewhere.

The most significant distinction is that a pump can work with liquids, while a compressor cannot. Liquids are much harder to compress. You may find a pump within a compressor, such as in a reciprocating air compressor &#; the part that performs the compression is a pump. The functions of pumps and compressors can overlap on machines where the pressure rises with each revolution.

Take a tire pump, for example. While it happens to perform both tasks &#; moving air and reducing its volume &#; its purpose is to move outside air somewhere else, into the air-tight space of the tire. Since its goal is not to reduce the volume, it&#;s not technically considered a compressor. An alternative example would be using pneumatic tools, which require compressed air. The device that reduces the volume of the air is a compressor.

Air pumps generally fall into one of two categories:

• Reciprocating pumps, which move back and forth. A bicycle pump is a reciprocating pump, where the cylinder pulls outside air in with a back-and-forth motion and moves it into the tire.
• Rotary pumps, also called centrifugal pumps, which spin. A rotary pump uses an impeller, which is basically an enclosed propeller. It has blades that move incoming fluid and send it through an outlet at high speed. This pump uses motorized energy to pull fluids from one place to another, and is not to be confused with a turbine, which captures fluids that are already moving.

Compressed Air in Everyday Life

From pneumatic drills and braking systems to HVAC units, a vast range of air-powered tools and machines make everyday life comfortable, safe and efficient. In nearly every building you walk through or pass by on a given day, air tools helped someone sand the wood, paint the walls and hammer beams and plasterboards into place. On shop floors across the world, people use compressed air to add coats of paint and blast dust and debris away.

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It&#;s nothing short of remarkable that humankind discovered a way to take ambient air, perhaps the most abundant resource on the planet, and transform it to power motorized equipment for a wide variety of purposes.

Quincy Compressor offers high-quality air compressors in many styles, including rotary screw, reciprocating/piston and oil-free. Use our sales and service locator to find a dealer near you.

Last Updated on October 22, at 3:30 pm

Millions of people use air compressors every day, but if one was in front of you, could you explain how it works?

You've probably seen where and how they're used over the years, but knowing the mechanics behind how the parts work together is more applicable than you might think.

Already know the basics? Read our Ultimate Air Compressor Guide to learn which type of air compressor is perfect for your application. This article is for the gearheads, the techies, and the innately curious.

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History of Air Compressors

Early humans might not have understood anatomy or physics, but they understood the potential of using forced air compressed by their lungs. By blowing on their fires, our ancestors were able to grow the flames into larger, more powerful sources of heat and energy.

Thousands of years later, the societies of the Iron and Bronze Ages had evolved to create useful tools that could be implemented on a larger scale. Metalworkers in China's Han dynasty used hand and foot-powered bellows to stoke the flames in their forges as early as the Third Century BC.

It wasn't until thousands of years had passed that an engineer named John Smeaton devised a way to compress even greater volumes of air in . His invention employed a water wheel to power a moving cylinder-a piston-that compressed air in a large chamber.

Smeaton's design led to further innovations, such as John Wilkinson's development of a machine with an efficient rotating cylinder in and George Medhurst's invention of a motorized air compressor in .

Since the days of wheels, belts, and metalwork, the most significant innovations in air compressors have taken place in the last 50 years. Today, the market continues to evolve to keep up with ever-increasing industrial demands.

Air Compressor Basics

The concept of compressed air is simple: when atmospheric air is stored under pressure, it creates potential energy that can be held inside a tank until it's needed. Just like a balloon being released, when the pressurized air is released, the potential energy is converted into usable kinetic (motion) energy.

By harnessing that transfer of energy through pneumatic (air) tools, we are able to work on tasks that were before impossible.

What is Air Displacement?

The core of how air compressors work is boiled down to two methods of air displacement.

In order to compress air, the internal components of a compressor must move or change position to mechanically force the air through the chamber where it is compressed and stored until use.

Positive Displacement is the method that most compressors use. Air is pulled into a
chamber that opens and closes, where the internal parts reduce the volume of the chamber and compress the air. Once the cycle is complete, the air is pushed through the chamber and into a storage tank where it waits to be used.

Piston, rotary-screw, and scroll-type air compressors all use positive displacement to compress and store air.

Dynamic (nonpositive) Displacement uses rotating blades on an impeller to pull air into the chamber, where the energy from the motion of the blades builds air pressure. Often used with turbocompressors, this method of air compression produces huge volumes of compressed air quickly, and this technology is commonly found in cars that use turbochargers.

Air compressors that utilize this method of displacement are often reserved for commercial/industrial applications when large volume flow rates and constant pressure are needed.

What Drives an Air Compressor?

Compressor drives are most commonly direct-drive or belt-driven systems. In a belt-driven system, as the motor turns, the belt turns with it, thus activating the pump in the system. This is the more economical option and is widely used across all compressor types because the belts can be adjusted to change with air demands.

In a direct-drive system, the motor attaches directly to the crankshaft of the compressor, allowing for smaller designs and fewer maintenance requirements. Although not much adjustment can be made to these drive systems, they are more efficient because less power is lost in the transfer of power to the crankshaft.

Another benefit of direct drive is the ability to provide compressed air without needing to fill a storage tank first, like using a DC compressor for off-roading.

The Mechanics of an Air Compressor

Depending on the type of air compressor, basic air compression requires an electric-powered motor, a pump with an internal mechanism to compress the air, an inlet/outlet valve to draw in and release air, and-in most cases-an air storage tank.

Air is drawn into the compressor where the internal components reduce the volume of the air by creating a vacuum, which drives the pressure of the air up as it is pushed into a holding tank. Once the maximum pressure is reached inside the tank, the duty cycle is complete, and the compressor shuts off until the pressure falls below a set threshold. Positive displacement air compressors do this in different ways: by using pistons, screws, and scrolls.

Reciprocating Piston Compressors

Piston-type air compressors operate similarly to the combustion engine in your car. When the crankshaft's rod raises the piston inside the cylinder, it forces air into the compression chamber. This decreases the air volume (thus increasing air pressure) as the crankshaft drives the piston closed and pushes the compressed air into a storage tank. Then, the piston opens again to draw more air in.

Piston compressors can achieve a full compression cycle (stroke) in 1 or 2 stages:

• Single-stage:
  The compressor uses a piston to compress the air in one stroke (a full rotation of the crankshaft that drives the piston a full motion). In some single-stage models, multiple pistons are used to divide up the work and can operate at lower RPMs and decibels.
  
  
• Two-stage:
  The compressor compresses air in one stroke using one piston before moving that pressurized air to a smaller cylinder for the second stroke from a second piston. This doubles the air pressure stored in the tank.

Piston compressors are notorious for being louder because the internal components rub together and create friction. However, advancing technology is improving the way they operate by introducing dual and multi-piston, single-stage models that use up to 4 pistons inside the pump. 

By using multiple pistons, the work of a single piston can be divided up, extending the life of the unit and achieving a supremely quiet air compressor.

View: Best Quiet Compressors

Rotary-Screw Compressors

Instead of using a piston, rotary screw compressors squeeze air between two helically-opposed screws that don't touch, reducing noise and maintenance.

These compressors were created for heavy-duty applications that require high power during extended periods and are ideal for maximum air intake and production.

Rotary screw compressors are oil-sealed and have fewer moving parts, so they operate more quietly and require less maintenance because of the design.

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Scroll Compressors

The third type of positive displacement compressor, scroll compressors, are known for their highly efficient, oil-free, and quiet operation. Similar to rotary compressors, the scroll design uses two interwoven metal pieces that work together but don't touch to create a vacuum.

Two spiral-shaped circular pieces rotate around one another to compress incoming air. One scroll is fixed in place and doesn't move, and the other fits inside the stationary scroll and moves in a tight circular motion without rotating.

Lubrication

Just like your car uses oil, air compressors need lubrication to continue running smoothly over time.

Lubricated air compressors use oil to reduce wear and friction on their moving parts. In the case of piston compressors, the oil is applied to the system in one of two ways:

• Splash lubrication: a dipper attached to the piston rod dips into an oil-filled trough and splashes the oil onto the piston and cylinder.
  
  
• Pressure lubrication: A pump sends oil through passages drilled inside the compressor, applying the oil to specific parts. Pressure-lubricated systems are generally more expensive, but the directed flow of oil keeps them operating longer than their splash-lubricated counterparts.

Non-lubricated compressors are also referred to as oil-less or oil-free because their parts are coated in special chemicals or materials like Teflon to reduce friction instead of conventional oil. The solution here is permanently-lubricated components. The drawback of non-lubricated compressors is that they heat up faster, and aren't the best option for heavy-work environments.

Most oil-less air compressors are used in industries where clean air is required for manufacturing, such as in the food, beverage, and electronics industries. For example, scroll compressors are used in the dental industry because of their continuous clean and quiet operation.

Oil vs Oil-Free Compressors

Measuring Power

When it comes to sizing an air compressor for airflow and air volume, there are two criteria professionals use to determine if an air compressor can properly handle an application and determine the kinds of tools that will be compatible with your air compressor.

1. Pressure is the amount of force applied to the surface of a given area. For compressed air and gases, this force is measured in pounds-force per square inch, or PSI. The higher the PSI rating, the greater the amount of force applied to the air within a compressor.

2. Airflow volume is a measure of the rate at which air can move into a compression cylinder and the machine can compress it. For air compressors, the volume of air is measured in
cubic feet per minute, or CFM. The higher the CFM value, the greater the volume of air a compressor can generate.

An easy way to understand how pressure and volume work together is to think of a garden hose. By putting your thumb over part of the hose opening, the same amount of water is forced through a smaller space, thus increasing pressure at a constant flow. By increasing the amount of water coming through the hose, more work can be done faster.

New Innovations in Air Compressors

Air compressor technology used to be expensive to produce and used a lot of energy to power, making it only affordable for the commercial industry. Even today, commercial air compressors still use significant energy.

As a general rule, you can expect to spend about $500 per horsepower (HP), per year using an industrial air compressor in continuous use. For example, a 10 HP compressor will generally equal $5,000 in operations costs per year.

In efforts to bring down costs and increase efficiency, new technologies are being introduced each year that innovate the possibilities and capability of compressed air. Engineers are finding ways to make compressors more powerful and energy-efficient, such as through variable speed drives (VSD) that allow the compressor to change motor speeds and voltage as air demands change, saving energy and money.

Even newer is the variable frequency drive (VFD) technology that takes this concept a step further. This technology allows the compressor to control the motor speed and torque by alternating from A/C to D/C power and controlling the input frequency and voltage, meaning the most efficient power usage available on the market.

Other innovations, including changes to the rotor speeds of rotary screw compressors, the use of water as a lubricant in place of oil, and the incorporation of remote monitoring systems all promise to deliver even greater improvements to efficiency in the near future.

The short of it is: air compressors aren't going to disappear, but instead continue to allow millions of people to get more work done faster and more effectively.

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