Air compressors play a crucial role in the pneumatics industry today, keeping factories and workshops open and running smoothly. However, they haven’t always been that way. In the history of the machine age, air compressors are a relatively new invention.
Many tools used to be powered by intricate systems that included belts, wheels, and other substantial parts before air compressors were invented. Typically out of reach for many small operations, this equipment was large, expensive, and heavy. These days, air compressors come in a variety of sizes and shapes, and you can find them in your neighbor’s garage as well as big shop floors and auto workshops. This article will explain how air compressors operate, covering everything from their fundamental operation to the various ways that different compressors handle air displacement.
Table of Contents
What is An Air Compressor?
Using an electric motor, diesel engine, gasoline engine, etc., an air compressor is a pneumatic device that converts power into potential energy stored in pressurized air (i.e., compressed air). A storage tank’s pressure rises as an air compressor adds air using one of several techniques. The air compressor turns off once the tank’s pressure reaches its upper-boundary design level.
The tank then stores the compressed air until it is required. 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. Since an air compressor operates on any gas or air while pumps operate on a liquid, they must be distinguished from one another.
How Do Air Compressors Work?
To pressurize a container with air, an air compressor must be used. The air is then pushed through a tank opening under pressure. The compressed air can be used as energy as it is released, similar to an open balloon.
An engine that transforms electrical energy into kinetic energy powers them. With a crankshaft, piston, valve, head, and connecting rod, it functions similarly to how a combustion engine does.
From there, a number of tools can be powered by the pressurized air. The more well-liked choices include sanders, paint sprayers, impact wrenches, and nailers.
There are various kinds of air compressors, and each one is used for a specific purpose. In general, the variations aren’t too significant; it all comes down to how a compressor manages air displacement.
How and Why Air is Compressed
Let’s first look more closely at the physics of compressed air to better understand its significance and the role that compressors play in producing it. Regular air is simply forced into a much smaller space to create compressed air. When this happens, its molecules speed up and so-called “kinetic energy” is created. Both immediate use and storage and release of that kinetic energy are options.
The versatility of compressed air is one of the reasons it has grown to be so essential. Compressed air is used in some capacity across a wide range of industries, including those in manufacturing, transportation (including automobiles, trains, and ships), and healthcare.
It makes sense that there are many different types of air compressors given the wide range of applications. After all, the compressor that powers a dentist’s drill shouldn’t be the same as the large, noisy compressor that powers an entire manufacturing facility.
Finding the Right Air Compressor
Finding the compressor that is best for them can be challenging for laypeople due to the abundance of options. Here is an overview of the various compressor types and technologies to make things simpler.
Let’s look at the operation of compressors first. There are two main compression technologies:
Positive displacement compressors have a cavity that is filled with regular air (or another gas at atmospheric pressure). As a result, the cavity shrinks, causing the air’s pressure and kinetic energy to increase as the same volume of air must fit into a smaller area.
Dynamic compressors achieve the required rise in pressure by accelerating the air (or gas) with an impeller and then slowing it down in a diffuser.
Positive displacement compressors use a variety of air displacement technologies and are much more widely used. Piston compressors use a reciprocating motion, rotary screw compressors a single rotor, and the more seldomly utilized scroll compressors feature a double rotor.
Each of them has unique advantages and applications.
For instance, inexpensive and comparatively simple machines include piston compressors. For operations with little need for compressed air, they are frequently the best option.
Modernized rotary screw compressors have a low total cost of ownership. In addition to producing much more compressed air, they are more energy efficient.
On the other hand, dynamic compressors are mostly employed in processes and applications that call for extremely high air volumes.
Differentiating Technologies
A compressor’s strengths and the best way to use it are determined by additional features in addition to their operating principle.
Oil-injected versus oil-free: High-quality air is not necessary for all applications. To inflate a tire, for instance, almost any compressed air will do, but compressed air that comes into contact with drugs or food must be extremely clean and adhere to strict regulations. The former is called “energy air” and the latter “active air.” Oil-injected compressors can work well for energy air, which typically needs to be less clean. However, the air they produce contains small amounts of oil, making them more expensive to buy and run.
They are therefore inappropriate for active air applications that require cleaner air. An oil-free compressor is a much better option in that situation because the air it creates is completely clean.
1-stage or 2-stage piston compressors: There are two types of piston compressors: 1-stage and 2-stage models. A less expensive 1-stage model will work for small tasks that don’t require a constant air supply. However, a 2-stage piston is probably a better option to run power tools and ensure a constant flow of compressed air.
Belt drive versus direct drive: When dependability, simplicity, efficiency, and power are the most important factors, belt-driven compressors are a better option. But a direct drive is typically preferred when applications require the compressor to be able to change its speed and power.
Fixed speed versus variable speed drive: Compressed air (and its production) makes up a significant portion of all energy used in the industrial sector, which is largely due to its wide range of uses and widespread availability. However, compressed air also requires a significant amount of energy to produce. In fact, the majority of a compressor’s total cost of ownership over its lifetime is accounted for by energy costs.
This brings up the distinction between compressors with fixed-speed and variable-speed drives. Fixed-speed models only have one speed, as the name suggests. That works well for applications or processes that demand a constant flow of air (of course, the compressor’s output would still need to be matched to the demand in order to avoid energy waste).
However, if the demand for air at a production site changes frequently, it is very inefficient. Variable-speed drive compressors are a far better choice in those circumstances. Although their initial cost is higher, they are much more efficient and have a much lower total cost of ownership because they use much less energy by adjusting the compressor speed to the air demand.
Types of Air Compressors
Based on their internal mechanisms, air compressors can either be positive displacement or dynamic displacement. The four most common types of air compressors you will see are:
- Rotary Screw Compressor
- Reciprocating Air Compressor
- Axial Compressor
- Centrifugal Compressor
Below, we’ll go over each type’s best applications so you can choose the one that works best for your project.
Positive Displacement Compressors
Air compressors that produce power through air displacement fall under the category of positive displacement compressors. This category of air compressors employs a variety of internal working mechanisms, but they all operate according to the same general principle.
The air from the outside is first stored in a cavity inside the machine, which slowly compresses to raise the air pressure and potential energy.
1. Rotary Screw Compressors
Because they have an internal cooling system and don’t need much maintenance, rotary screw compressors, a common type of displacement compressor, are among the simplest air compressors to maintain. They are typically large, industrial-sized devices that can operate with or without oil lubrication.
Two internal, anti-clockwise rotating rotors in rotary screw air compressors are the source of energy. Between the two opposing rotors, air becomes trapped, creating pressure inside the housing. These air compressors, which range in power from 5 horsepower to 350 horsepower, are built for continuous use due to the internal cooling system.
2. Reciprocating Compressors
Reciprocal compressors are another common variety of displacement compressors. These are typically found at smaller construction sites, like garages and residential homes. The reciprocating compressor, in contrast to the rotary screw compressor, is not intended for continuous use.
Compared to a rotary screw compressor, a reciprocating air compressor has more moving parts that are lubricated with oil for smoother operation.
These air compressors function by compressing and displacing the air inside a cylinder to increase pressure. The pressure ranges that reciprocating compressors are capable of producing depend on whether they are single- or multi-stage.
The multi-stage compressor is the best option when you need more power. Multi-stage compressors offer the power required for demanding construction, such as auto assembly and maintenance, whereas single-stage compressors are adequate for smaller projects like woodworking and metalworking. Reciprocal compressors with multiple stages have a maximum horsepower of 30.
Dynamic Compressors
Dynamic air compressors produce horsepower by drawing air in with quickly rotating blades and then limiting the air to create pressure. The compressor then stores the kinetic energy as static energy.
3. Axial Compressors
Axial air compressors are more frequently found in high-speed engines on ships and airplanes than in construction projects. They can produce up to many thousands of horsepower but are significantly more expensive than other types of air compressors, which is why they are primarily used in aerospace research despite having a high-efficiency rate.
4. Centrifugal Compressors
To create potential energy, centrifugal air compressors diffuser the incoming air through a slowing and cooling process. Centrifugal compressors can generate a lot of energy in a small machine because of the multi-phase compression process.
They require less maintenance than reciprocating or rotary screw compressors, and some varieties can produce air without oil. They are frequently used for more challenging construction sites, such as chemical plants or steel manufacturing facilities, as they have a maximum horsepower of about 1,000.
Air Compressor Power Supply
The most popular types are electric compressors. They operate in any dry area with an available electrical supply, are quieter than models powered by gasoline, and require less maintenance. Electric compressors are appropriate for use indoors.
Most household compressors for use at home run on a 120-volt supply, but larger models might have different needs. Mobility is restricted because a portable electric compressor needs an appropriate extension cord.
Inflators can be plugged into either a 12-volt or 120-volt household outlet, depending on the model. Air compressors that are powered by gasoline are a good option for outdoor workspaces where electricity is scarce or nonexistent. They typically produce more PSI because they have more horsepower than electric models.
Air Compressors and Air Tools
An air compressor’s primary purpose 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 specific volume and pressure needs. For the compressor to work properly, it must fulfill these specifications. Think about the tools you want to power with the air compressor when making your selection.
Choose the one that requires the most CFM at the most PSI. Search for a compressor that satisfies the requirement by adding 50% to the necessary CFM as a margin of safety. 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
In order to choose the right model, you should understand the air compressor features that can handle your jobs and simplify your work:
- A pump that doesn’t mix oil into the compressed air is less maintenance-intensive.
- When compared to a direct-drive system, belt drives operate more quietly.
- To protect against overload damage, thermal protection shuts down the motor.
- You can steer exhaust away from your workspace with adjustable exhaust.
- Without connecting and disengaging tools, you can manage different tasks with multiple couplers.
- Your investment is enhanced by including tools and accessories like hoses, nailers, and blow guns. Air hoses are not always included with compressors.
- To increase the amount of air you can store, you can purchase 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 moderate pressure, clean air to a diver working below the surface, and providing moderate 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 lot of high-pressure air to fill high-pressure air tanks (HPA), power pneumatic tools like jackhammers, and fill tires.
Air compressors are also widely used in oil and gas, mining, and drilling applications as the flushing medium, aerating muds in underbalanced drilling, and air pigging of pipelines.
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.
