What Is An Air Compressor?
What does an air compressor look like?
Air compressors come in a variety of shapes, styles and sizes. Engineers have developed various styles just to suit as many needs for pressurized air as possible. These styles range from the pancake compressors which are usually the smallest to the much larger industrial cabinet types.
Pancake air compressors
You will recognize the pancake air compressor from its distinctive pancake-shaped air tank and pump. Their tank size is typically between one and six gallons.
Hot dog air compressors
The other common type of air compressor called the hot dog compressor is just like the name suggests; it has an extended air tank that looks like a hot dog. It is usually described alongside the twin stack air compressor, which is a combination of a pair of hot dog air compressors.
Wheelbarrow air compressors
Slightly larger than this style is the wheelbarrow air compressor, which is essentially still a hot dog air compressor. It has a wheel and handles and could be confused for a mobile electric generator.
Stationary air compressors
Some air compressors are larger than this one – the stationary ones. They are huge and heavy. For those applicable in industries, they even come with service panels that make them reliable.
What does an air compressor do?
An air compressor is designed for application in different levels of industries. Indeed, this device is a requisite for most garages, factories, and workshops across the globe. Many people have air compressors at home to help them in different projects/tasks.
Given its capability to generate compressed air (an energy source), the air compressor acts as an indispensable partner to many tools and equipment.
An air compressor is extremely popular because it does numerous things. As its name implies, the equipment generates compressed air and stores it within a tank. The air in the tank can transfer to a piece of machinery or tool and perform work because it carries kinetic energy.
This means that the air compressor can do jobs in as many places as you can imagine. On top of garages, air compressors are useful in deep-sea diving, paint booths, auto service stations, and tire shops among many other areas.
What is an air compressor used for?
Air compressors for home use
Inflating Car Tires
One of the most popular applications of the air compressor at home is inflating car tires. A typical car tire requires around 35PSI of air pressure. Of course, agricultural and other larger vehicles may require higher pressure. But that should not cause any problem for a regular air compressor because it can easily generate 100PSI.
When it comes to the flow rate of the air compressor for inflating car tires, a higher rating would mean that you can inflate the tire faster. A simple air compressor rated at 2 CFM @90 PSI should serve you fine. If you will be using the device for other jobs apart from inflation, follow the rule of thumb: Calculate the total CFM requirements for all the tools and multiply by a safety factor of 1.5.
Note that the best air compressor for inflating tires or supporting any other home pneumatic tool should be immune to overheating.
In short, an air compressor can easily inflate car tires at home. It is fine to use the air compressor to inflate car tires because the air will be moisture-free. Furthermore, the best air compressor delivers pressurized air at the correct temperature.
Unless you are spray painting using an HVLP type or airless model, you need a quality air compressor to complete your job successfully. As long as the compressor has the right pressure airflow rating, you should have a flawless process.
Maybe not completely flawless if the tank size isn’t enough. A large tank is preferable for an air compressor for this job. About 50 gallons would be recommendable because this would help you finish the job evenly.
Regarding the CFM rating of the air compressor, you always want the device to exceed the airflow rating of the spray gun. Best spray painting needs about 12CFM (for the slightly expensive spray guns) so make sure the compressor slightly exceeds this.
Remember that the air compressor doesn’t have to be specially made for spray painting – provided it can deliver enough pressure to the spray gun, consider that air compressor for the job. Therefore, if you have such an air compressor at home and use it for other tasks, just invest in a spray gun and you will be ready to go.
Many people wonder if the air compressor can be used for pressure washing. With the craze for equipment that can multitask, it is not a wonder that people are using the air compressor for different applications, including pressure washing. You guessed it right: You can get an attachment for pressure washing and you will be able to pressure wash your sidewalk, patio, and many other areas.
But it’s good to remind what a pressure washer is to show the difference from an air compressor. The pressure washer is solely designed for removing surface dirt such as mold and paint. In simple terms, it is a mechanical sprayer.
On the contrary, the air compressor is designed to convert electric power into pressure, a form of potential energy.
The air compressor may work as a pressure washer, but there will be some pressure difference. Whereas the typical air compressor generates 100 PSI more or less. The pressure washer gives much higher pressure of up to 3500 PSI.
For your air compressor to give results that are close to that of a pressure washer, you want to boost the air pressure using smaller nozzles and focus the air stream.
Please see our full guide Can you use an air compressor as a pressure washer? for more information on this subject.
Every carpenter wants to finish their project without issues. A carpenter may need an air compressor to perform various tasks in woodworking.
The first one is powering of pneumatic tools. You can use the air compressor to operate tools like sanders, paintbrushes, nail guns, and screwdrivers.
The relevance of the best air compressor for carpentry is the delivery of consistent pressure that is needed to perform the jobs thoroughly. On top of that, the air compressor minimizes injury and ensures less fatigue to the user. With the air compressor as part of the tools, the carpenter deals with less noise.
As a carpenter, the air compressor that is best for your work mostly depends on your CFM requirements.
Yard work covers many activities including mowing, watering, and collecting dry leaves. You can be creative with your air compressor for yard work to keep the yard in good shape.
Inflating vehicle tires is a popular maintenance activity for yard equipment. Many homeowners like to maintain their yards using a lawnmower, for instance. Once in a while, there is a need to inflate these tires.
Industrial uses for compressed air
Air compressors play a wide range of roles in the industrial sector. Industrial setups across the globe have for many years relied upon the industrial compressor to accomplish tasks fast, safely, and energy-efficiently. Indeed, there are industrial air compressors, which are purposely designed for the heavy-duty requirements of these facilities.
The sectors of application are many, so we choose to cover the most popular ones: Automotive, manufacturing, and farming.
The ideal performance of a motor vehicle is a result of high-quality assembly, repairs, and maintenance. There are the basic parts that ensure that the vehicle can move, but the exteriors also need attention. Therefore, an automotive workshop needs a good air compressor.
Air compressors enable automotive professionals to perform numerous tasks within and outside the garage. They support pneumatic tools such as power grinders, air saws, and impact wrenches. Technicians also use air compressors for spray painting, tire inflation, and much more.
The widespread application of air compressors in the automotive field has prompted many automotive facilities to be keener about choosing the best air compressor for various tasks. Alongside selecting the right air compressor for a specific job is the need to use the device correctly.
Automotive facilities need compressed air for maintenance jobs and other applications. But overall, the compressed air should be dry and free from impurities. Such air comes in handy for;
- Tire inflation – Compressed air in a tire is essential for preventing wear and tear
- Auto Painting – The motor vehicle needs to be appealing to the eye. Air compressors are applicable in surface treatment, which includes finishing and painting.
- High-pressure cleaning and washing – Some parts of the vehicle (for instance the engine block) are difficult to reach. When such places need cleaning, doing so using an air compressor is effective
- Operating Pneumatic Tools – Ease of operation and weight are the most important considerations for an automotive tool. Pneumatic tools are more popular than electric tools for these reasons.
Automotive workshops have several types of industrial air compressors to choose from. When a consistent supply of high-pressure air is necessary, you want to get a rotary screw air compressor. Because airflow needs will vary, there are many models and sizes of these devices in the market. Although these air compressors are difficult to operate and are relatively expensive, they are popular for their long lifespans and quiet operation.
If you were looking for a low-maintenance, energy-efficient unit, I would recommend a piston air compressor. The other name for this type is reciprocating air compressor. These air compressors need to cool down after a particular time slot, so they are unsuitable for continuous operations. They may also be loud, but they are low maintenance and relatively affordable.
The air compressor is a pivotal device in the manufacturing space because it helps accomplish countless jobs. It is used either intermittently or continuously in various segments of this industry.
For instance, in metalworking, the air compressor does things like spraying, injection molding, actuators & controls, and powering tools.
In the food and beverage segment, compressed air comes in handy in material handling, bottling, dehydration, and spray coating.
Air compressors promote the plastics segment through injection molding, powering tools, press powering, and clamping.
Clamping, powering tools, and spraying are some of the jobs that the air compressor enhances in the furniture segment of manufacturing.
Manufacturing applications usually have these types of air compressors:
- Rotary screw
- Rotary vane
Agriculture is one of the industries that use the air compressor extensively. The air compressor can be used in a wide range of jobs on the farm, and farmers continue to discover new ways of using it.
With numerous uses of the device in farming, you may even find yourself investing in several of them.
All-terrain vehicles are prominent on farms. To keep their tires with adequate PSI, you need an air compressor at hand. The same case applies to trailer tires. You don’t want to fail to respond to an emergency on the farm because one of the tires was flat.
Farmers prefer to do some projects on their own. Most build machine shops, chicken sheds, cattle fences, and the like. Pneumatic nail guns are common on the farm for such projects. To run the gun, an air compressor is necessary. When you have the typical air compressor, you can use the nail gun for various tasks.
Indeed, a brush can be enough to paint the barn, garage, or even home. However, this outdated method is no match to the efficiency of a painting gun connected to an air compressor. The work is devoid of messes or unevenness.
The air compressor does a lot more for the farming industry including powering gates, cleaning equipment, and dairy farming.
How an air compressor works
How does air compression work?
The basic working principle of an air compressor is compression of air once it enters the device and release of the same at high speed and pressure on the other side. A common air compressor has a storage tank, an electric motor, inlet & outlet valves, a pump, and air discharge.
In essence, the operation is divided into several stages.
First, there is the air intake stage. To form compressed air, the device must first draw the air. Air enters the air compressor through the intake valve.
Following in the second stage, also called the compression stage, is the compression of the air in a compression chamber. This involves the conversion of kinetic energy in the air into potential energy or pressurized air. Depending on the compressor type in question, how this is achieved may vary.
The next stage is called integrated storage. After the air compression process, the air may be directed to a storage tank or air tank. For limited duty units, the air is stored so that it can be availed during downtime. Shop compressors have this kind of storage. Some compressors store air and use it when running at low capacity. They have controls to enable them to operate like this, hence their name “modulating compressors”.
Integrated cooling follows integrated storage. Because of the compression process, the air becomes hot. While cooling the air before it leaves the air compressor is not a must, some diesel units and the majority of three-phase electric units come with the cooling capability to reduce the temperature. Typically, an after-cooler works together with a water separator to remove the moisture that is generated from cooling.
Discharge is the last stage in the operation of an air compressor. As the air flows to the discharge point, it may move directly to the point of use or go through a set of filters and dryers first.
Because of this capability, air compressors are applicable for supplying air to mechanical equipment and forcing air into small enclosures.
I actually found a great little video on YouTube which demonstrates how a compressor works better than I can in words! Credit to Learnchannel.
What is in compressed air?
As you may have predicted, compressed air is just air which has been put under pressure to be compacted into a smaller space. Since air is a mixture of gases, it is composed of many gases. Predominantly, these gases are nitrogen with 78% and oxygen with 21%. Compressed air comprises a variety of molecules that carry kinetic energy.
The mean kinetic energy in the molecules determines the temperature of the compressed air. If the kinetic energy of the air is high, the temperature also rises, and vice versa.
Compressed air is perfect for energy storage and transmission. Its versatility and flexibility are the most appealing characteristics. Unlike batteries, compressed air has a higher charge life.
Although compressed air is less cost-efficient than electricity, it is still preferable owing to its relative safety. Pneumatic tools can use compressed air under numerous conditions, unlike electricity.
Compressed air also offers the advantage of flexibility. You can use it on construction sites in remote areas, and use variable torque and speed in any form of tool. The same cannot be said of electric-powered tools.
Don’t forget that tools designed to use compressed air are more affordable than electric-powered ones. Owing to their simple design, these tools need fewer parts. They are designed for tough environments, so they tend to last longer.
Did you know that compressed is among the leading utilities? Alongside gas, water, and electricity, compressed air is the most used utility.
What is a Reciprocating Piston?
A reciprocating piston is one of the main components of the reciprocating compressor. The other components include bearings, valves, cylinders, and a frame. Also part of the setup is piston rings, crankshaft, crosshead, and connecting rod.
The piston moves within a cylinder and compresses air in the process. Two sets of piston movement are notable: downwards when the piston draws air in, and upwards when it compresses this air. Two valves control the air movement in and out.
The reciprocating piston of the air compressor must be strong and heavy enough to compress the gas correctly. Its material must also be compatible with the gas.
As the reciprocating piston moves up and down inside the cylinder, it comes in contact with the cylinder walls. Instead of direct contact, piston rings cover the piston.
A lot of friction is generated in the cylinder as reciprocating piston compressor work, so the piston rings are bound to wear and tear. Frequent replacement is necessary for piston compressors.
What Is Air Displacement?
Air displacement is often mentioned alongside any air compressor. It is the basic concept of an air compressor. Every air compressor has an internal mechanism that moves and pushes air.
Air displacement can be either positive displacement or dynamic displacement.
In positive displacement which is in most air compressors, the device compresses air by reducing the volume of the container. The air then moves on for usage or storage.
Dynamic air displacement involves the use of a rotating impeller to force air into a chamber. As the blades of the impeller move fast, they create a strong force within a short time. You will find this concept in vehicle turbochargers.
How Does an Air Compressor Regulator Work?
As the air flows from the air compressor under pressure and into the pneumatic tools, it needs to be controlled. That’s the work of the regulator. Since this component adjusts the air pressure according to the tool requirements, it helps sustain the integrity of your tools.
When working correctly, the regulator maintains uniform air pressure notwithstanding the input pressure and the flow requirements of the tool.
Except if it is a uniquely made one, the air compressor regulator allows airflow in only one direction, and that direction will be shown by an allow on the item.
The regulator has an intake port, which connects to the air compressor. Once connected, you can control the airflow according to the requirements of your tool. Your application will connect to the outlet port of the air compressor regulator.
To use the air compressor regulator, first, disconnect the air compressor from the socket. Check close to the motor for the cut-in pressure knob. Set it to your desired level. Set the cut-out pressure too. Now you can plug in the compressor to the power socket. Once the air compressor tank is full, you can connect your tool to the unit using the air hose.
Most regulators have their regulator knob on the right side, but it is recommended to confirm it. Typically, a difference of about 20PSI is advised between the cut-in and cut-out pressure. Note that the cut-out point is higher than the cut-in point.
To be honest, using and reading the air compressor regulator is simple. Just follow the indicator on the regulator, knowing that it will move according to the pressure in the tank. The most important point is that PSI shown on the regulator should go with that of your tool. If not, you may end up having a poorly working tool.
In case the air pressure is dangerously high, a safety valve swings into action. Please note that you should never tamper with this valve, save for when you want to replace it with a new one.
What size air compressor do I need?
As you head out to buy an air compressor, this is one of the basic questions to ask. You cannot run away from it because if you size your air compressor wrongly, you are bound to experience problems in your jobs. A poorly sized air compressor not only makes your work tiresome but also brings energy inefficiency. You will find yourself using more energy and time on the job than normal.
But the size of the air compressor in most instances refers to the airflow and PSI figures for the device. Start with your air tools, specifically their highest value of airflow (CFM) and PSI. Use a safety factor of 1.5 on the value to get the ideal CFM and PSI for the air compressor. Your task now will be to find an air compressor that best matches this figure. For instance, if the spray gun requires 12CFM @90PSI, the air compressor should at least deliver 18CFM @90PSI.
Here are some common air tools with their estimated CFM requirements:
- 1-inch impact wrench – 10
- Air hammer – 4
- 3/4-inch impact driver– 7
- Brad nailer – 0.5
- Framing nailer – 2.2
- 1/4- inch ratchet – 3
- Grease gun – 3
- Drill – 4
However, there are other elements of an air compressor size that come into play, including the tank size/capacity.
There are so many shapes and orientations of air compressor tanks in the market. Without a doubt, most people would want to pick the largest size because it has more air. More air means that the air compressor can handle more work before it needs to refill.
However, you want to consider the cons of a big tank too.
The first one is that bigger tanks tend to be more expensive. Also, a bigger tank will be more difficult to carry or store because it is bulky. If most of your jobs need you to move up and down, a large tank may be undesirable. There are tanks as big as 80 gallons and they can be sizeable.
The question now is how to determine the best size for the tank. It all boils down to the nature of your work or the type of tools you are using. If your job requires the tool to work continuously, a larger air compressor tank is highly recommendable.
It will take some time to empty and refill (the recovery time). There is nothing wrong with having a large tank for tools that work intermittently. The tank may never go empty and that’s a plus. However, such a tank may be unnecessary, especially if you are buying on a budget. If you are only using brad nailers or such tools that require small bursts of air, you can invest in a small tank, say 2 gallons. The tank will drain very slowly and you will get time to refill it.
The physical dimensions of the air compressor in comparison to the space available are an equally important consideration. Air compressor tanks contribute the most to the physical dimensions of the unit. To make servicing easy and promote airflow around the air compressor, allow at least a 3-foot radius around the equipment.
Then there is the power capability of the air compressor given in horsepower (hp) rating. It is the mechanical energy required for the air compressor to operate or compress air. It is indicated by the power rating of the motor. While sizeable stationary air compressors can be as powerful as 15hp, most air compressors are within the range of 1.5 to 6.5 hp.
See our long-form comprehensive guide called What size air compressor do I need? for more detail, and real world data for 41 tools and uses.
What is air compressor CFM?
The most reliable indicator of the capability of an air compressor is the volume of air that the unit can deliver at a given pressure. Pressure and volume are inversely proportional so one parameter increases when the other one decreases. CFM itself refers to cubic feet per minute and is the rate of compressed air delivery.
Without a corresponding pressure at discharge, CFM may not mean a lot. The CFM of an air compressor is influenced by relative humidity, air temperature, and atmospheric pressure. That’s why you will find some air compressors rated with Standard Cubic Feet per Minute (SCFM). This simply means that the CFM rating was determined at sea level, 68F temperature, and relative humidity of 35%.
Normally, manufacturers will take the CFM rating of the air compressor as the product of the motor RPM, the cylinder bore, and the cylinder stroke. In this case, the variables mentioned above are not in the equation. Some CFM ratings are also based on the PSI of the air compressor.
See our full guide to air compressor CFM for more detail.
Let us now look at the PSI.
What is PSI in air compressors?
Pounds per square inch (PSI) is a measurement for the air pressure subjected to a unit square in area. Like the parameters already discussed, the PSI of the air compressor is an important consideration because you need to match it with the parameters of the tool.
Air compressors come with different tank pressure or PSI ratings. Pick the most ideal pressure range for your tools. Most pneumatic tools will work perfectly with 90PSI. Tire inflation may demand as much as 130PSI depending on the task. 60PSI may be enough for the paint gun.
Mostly, the air compressor will come with a standard PSI setting. For instance, a shop air compressor may be rated at 115PSI.
Every air compressor has a “cut-in” and “cut-out” pressure. The cut-in also called the reset point, is the pressure at which the air compressor starts. The device stops working at the cut-out point also called the trip point. The difference between the two points is referred to as the pressure differential or pressure band.
Note that lower air compressor pressures go with higher cfm while higher pressures result in less cfm. Considering that cfm is the backbone of the operation of the tool, you want to select the PSI of your unit carefully. For instance, if your shop has an inflating machine that requires 115PSI yet every other tool is rated at only 90PSI, an air compressor rated at higher than 115PSI is recommended. A 145PSI rating for the air compressor would be ideal.
For more info on PSI, see our guide What PSI compressor do I need?
What is air compressor duty cycle?
The duty cycle of an air compressor is the duration the machine can run before resting. As the air compressor runs, it has to generate consistent airflow (CFM) and pressure (PSI). This factor is critical if you intend to use your air compressor for extended periods. The typical air compressor has a duty cycle of about 60%. Larger air compressors can have a higher rating, even 100% for the gas-powered varieties.
What does a duty cycle of something like 50% mean? For a cycle of 10 minutes, the air compressor runs for 5 minutes, or half the time. That’s what the 50% is about.
In other words, if the air compressor has a duty cycle of 50%, it will give you a runtime of 30 seconds each minute.
If you are a hobbyist just doing simple projects at home, I don’t think the duty cycle should concern you a lot. Or do you use the air compressor frequently often? However, in professional applications where the pressure for timely results is high, the duty cycle is a priority. For each minute that the air compressor rests, the operator risks losing some money.
For more detailed info on this, see our guide What is air compressor duty cycle?
Does HP matter in an air compressor?
The power or horsepower (HP) of the air compressor is an equally important consideration. This parameter represents the amount of power that the motor or engine of the air compressor gives. It was first used by Engineer James Watts in the 18th century as a literal comparison to draft horses’ power.
Unless your air compressor is meant for industrial use, its horsepower should be in the range of 1.5 to 6.5 HP. The amount of horsepower for the air compressor determines the amount of power the unit can generate. A higher rating means that the compressor can run larger or several tools concurrently.
I am sure you have come across these terms: “peak hp” and “running hp”. The running hp is the amount of horsepower the air compressor can achieve when working continuously. The peak hp is the highest amount of horsepower the air compressor can offer for a short time.
As you may guess, a high running hp is preferable to a high peak hp since this allows you to complete your jobs without strain on the air compressor.
How loud is an air compressor?
You may be wondering why air compressors tend to be so loud. Maybe you have never come across a silent air compressor.
There are many reasons why air compressors are loud, but the major one is friction. When metal slides against or hits another metal, noise forms. Usually, if the air compressor has many parts, it will also be louder. This applies to the device’s motor too.
The argument is the same when you look at the gas-powered air compressor. The types of air compressors are normally louder than the electric types because they have more moving metal parts.
Apart from friction, the surrounding of the air compressor can be the source of the noise. For instance, concrete walls and floors tend to amplify even the slightest noises. So your compressor may not be that loud, but the environment makes the unit sound so.
To know how loud a compressor is, the decibel (dB) is often used. Louder noise has a higher decibel measurement and vice versa. Note that this scale is not as straightforward as most people may think. A 60dB sound is slightly louder than the double 30dB sound.
Because the styles, designs, and sizes of air compressors differ, the loudness/quietness of air compressors differs as well. Modern air compressors have noise levels of 40 to 92 decibels. That gap is huge, isn’t it? One air compressor is deafening during operation while another one is at conversation level.
Rotary screw air compressors are some of the quietest in the market at about 63 decibels. If you own one, you will notice that the loudness increases over time. This is because the parts wear and tear gradually, so the unit increasingly struggles to deliver the same level of performance.
The pancake air compressor is slightly louder at about 73 decibels on average. Still, this noise isn’t so bad because the users can still operate comfortably – no irritation whatsoever. An oil-free design is a big plus because the air compressor doesn’t demand a lot in terms of maintenance.
The good news is that there are ways to deal with air compressor noise. You could start with the air compressor itself, specifically by performing proper maintenance. Given that the device has many parts that are prone to wear and tear, make lubricate the moving parts as recommended to keep them in good shape. For more on this, see our guide How to Make an Air Compressor Quieter.
To minimize the amount of dirt that finds its way into the system, keep the air filter clean. This reduces the strain on the air compressor. However, you want to leave the handling of unexplained loudness to experts. Schedule regular maintenance to deal with such issues.
Other ways to deal with air compressor loudness are:
- Wearing hearing protection
- Installing intake silencers
- Placing air compressor in a sound-proof enclosure
- Use sound-reducing materials, for instance, on the floor
- Reduce your proximity to the air compressor
What is air compressor oil?
Moving parts in the air compressor such as screws and pistons need regular lubrication to minimize friction. Therefore, it is important to check whether the air compressor oil level is okay and add it where necessary.
As long as an air compressor is not oil-free, it requires oil for lubrication of the moving parts. Compressor oil may be found in oil-flooded rotary vane compressors, rotary screw air compressors, and reciprocating air compressors.
Industrial applications normally have oil-flooded rotary screw air compressors for processing lines, powerful tools, and pneumatic conveyors. The use of oil during compression performs the following primary roles: cleaning the system, lubricating the moving parts, forming an air seal, and cooling the air.
Once you are sure that your air compressor requires oil, make sure that you use the right type of oil. Depending on compressor type and the operating conditions, there are different types of oils/lubricants available for air compressors:
- Polyol esters (POEs)
- Synthetic hydrocarbons (POAs)
- Polyglycols (PAGs)
- Blended products
- Food-grade oils
If you need help maintaining your air compressor concerning oil, you can always contact an expert.
For much more detail on the subject of oil, please see our guide What is air compressor oil?
Oiled vs. oil-free air compressors
When looking for an air compressor, you will need to choose between oiled and oil-free. There may be no difference between the two as far as function is concerned, but their operation and design vary.
In the oil-free air compressor, there is no oil on the cylinder walls. Instead, these air compressors self-lubricate using special materials. Movements such as that of the piston within the cylinder rely on sealed bearings.
Oiled air compressors use oil within for the moving parts. Oil performs several functions including sealing air and lubricating the parts.
If you are looking for a lighter and more affordable air compressor, consider an oil-free one. This one is likely to have fewer parts and therefore lighter. Most of them are more affordable than their oiled counterparts.
For industrial applications, you want to work with oiled air compressors for their longevity. The performance of oil-free air compressors is limited, so they are mostly suitable for domestic use.
For more detail on this, please see our guide called Oiled vs oil-free air compressors.
Types of air compressors
In the history of air compressor applications in automotive and related industries, the piston (reciprocating) air compressor is the most popular. But this long history or age of this air compressor should not deceive you. Reciprocating air compressors are some of the most suitable for the job.
All reciprocating air compressors have a piston that is driven by a crankshaft. The piston compresses air, increases pressure, and essentially the potential energy.
There are different sizes of reciprocating air compressors, so keep this in mind when buying this type. Your application will determine which size you choose – more cfm requirements would demand a bigger air compressor. If you want to use as little space as possible, consider investing in a vertical tank reciprocating air compressor. If you don’t mind about space in your workshop or job site, either a horizontal or vertical tank can do.
Dynamic Air Compressors
Dynamic displacement air compressors do not physically reduce the volume of air; they increase its velocity and minimize airflow so that when they reduce the velocity, pressure increases. Naturally, these air compressors are oil-free. Popular air compressors in this category are centrifugal and axial types.
Centrifugal air compressors
Centrifugal air compressors feature an impeller that draws air. This component accelerates air towards the outer edge before releasing it on an outlet scroll and diffuser plate. As the velocity of the air decreases, pressure increases.
Axial air compressors
Axial air compressors have a sequence of turbines like those of a jet engine. The blades force air into a small space. Axial air compressors may offer substantial flow rates and high efficiencies, but they are not common in the market. Apart from being susceptible to flow disruptions, this type of compressor is expensive and difficult to manufacture.
What is a single-stage air compressor?
Many people are looking for a single-stage compressor for their simple jobs at home. This compressor is popular for its durability, but only if restricted to light jobs. For heavier applications, you need a 2-stage air compressor.
A single-stage air compressor has one piston and one cylinder. Simply put, the air is compressed once in a single-piston stroke, hence the name single stage. It also features a pressure-sensitive valve. You may also call this type a piston air compressor.
The force that compresses the air comes from a power source, which is connected to the cylinder. Single-stage air compressors are applicable for spray painting, granite cleaning, liquid transfer, tools, and so forth.
What is a two-stage compressor?
As the name suggests, a 2 stage air compressor features two cylinders and two pistons. One piston forces air from one cylinder to another, thus increasing the pressure significantly. This air compressor can be electric or gas-powered. Since they are more powerful than the single-stage type, these air compressors find application in more demanding areas. For instance, they can be used in petrol pumps and textile industries.
What are Positive Displacement Compressors?
Positive displacement air compressors introduce air into a chamber and then compress it mechanically through volume reduction. The name positive displacement emanates from the fact that the device compresses air by displacing volume in the cylinder. An important part of this setup is the reciprocating component. This component moves back and forth in the compression cylinder.
Positive displacement compressors are affordable, reliable, and versatile. You can use them for chemical plants, refrigerators, LPG industries, and fertilizer industries. Unfortunately, you may not use this type where continuous flow of fluid is required.
Reciprocating, rotary vane, scroll, and screw compressors all belong to this category.
More on these types of compressors are covered next.
What is a Scroll Compressor?
The scroll air compressor derives the name from its unique way of sucking and compressing air. It uses a pair of spiral-like elements that are connected. One of the scrolls is stationary while the other one has orbiting capability. As the scrolls oscillate continuously, the crescent-shaped spaces compress the air. There is no metal-to-metal contact between the scrolls during the operation.
The rotating scroll gets power from a crankshaft and suctions air into an opening. As air moves in the pockets, it is continuously compressed and directed towards the center of the scrolls. An outlet port located at the center collects the compressed air and directs it elsewhere with the help of a non-return valve.
Scroll compressors have a relatively simple design but are very efficient. Fewer parts mean that operational reliability is high and maintenance requirements minimal.
What is a Rotary Screw Compressor?
The rotary screw compressor is popular for applications in many industrial applications and processes. The air compressor is defined by the use of rotary movements in air compression. Male and female rotors within this device operate systematically to trap air. The meshing of these rotors without contact is possible thanks to the concave cavities and convex robes in the female rotor and male rotor respectively. The male rotor features fewer lobes than the female rotor does to ensure that the rotation is quick. In its wide range of applications, this type of compressor offers benefits such as high energy efficiency, maintenance ease, low noise, and power.
What is a Rotary Vane Compressor?
The rotary compressor comprises a rotor carrying vanes rotating within a cavity. Radial sliding vanes are connected to the cylindrical rotor via slots on the rotor. Adjacent vanes create pockets that decrease in volume as leave the inlet port and proceed towards the exit port. If you need a continuous supply of air, you may want to try this air compressor. The device is common in beverages, manufacturing, automotive, and agriculture among other applications.
Fixed Speed Compressors vs Variable Speed Compressors
You may have heard recommendations to upgrade from a fixed-speed air compressor to a variable-speed one. The most prominent reason for such a switch is energy savings. Unlike the fixed-speed type, the variable-speed compressor will always match the compressed air demand with the power needed to run it. A fixed speed air compressor has standard RPM for all requirements. Even if you wanted just a little amount of compressed air, the air compressor will still run at full speed.
The variable-speed compressor has other advantages such as lower starting current and durability. However, this doesn’t mean that everyone should overlook the fixed speed type. If your facility is running on a budget, you may find the fixed speed option better for the time being. The air compressor may also be more economical in operations where CFM variations are insignificant or minimal.
There are also times when you may need the two types of air compressors. A professional system engineer can always help you decide the way to maximize both variable speed and fixed-speed air compressors.
Rotodynamic or Turbo Compressors
The rotodynamic or turbo air compressor is a type that is characterized by special mechanisms imparting kinetic energy to the air. The centrifugal compressor is one of the notable rotodynamic compressors. These air compressors are popular for processes that require medium-to-high flow rates and oil-free environments. Although they are expensive to maintain, rotodynamic compressors are reliable in chemical, food production, and similar industries.
What Is the Difference Between a Pump and a Compressor?
If you want to tell the difference between these two devices, you need to look at their function, design, application, and such angles. While the pump moves liquids and gasses from one place to another, the compressor only deals with gasses. Another difference is that air compresses are designed to reduce the volume of the gas, but pumps don’t alter the volume of the fluid.
When you look at the design, air pumps tend to have only basic components – motor, shaft, impeller, and a few others. But the air compressor has many components that include a storage tank, filter, and valves.
How much is an air compressor?
Many people looking to own the best air compressor wonder what the cheapest air compressor is. It is not a simple question to answer because many considerations are involved.
Typically, the air compressors for the home are the cheapest while industrial types cost a lot more.
If you want an air compressor for a home shop, you might need something too big. About 5 gallons in capacity would be enough. You will not go for the most powerful option, as the compressor won’t be working hard as the professional ones.
Depending on your requirements and budget, you could spend between $100 and $500 for this kind of air compressor. If you are regularly using your air compressor for pneumatic tools, you may want to go for something closer to this.
However, if your compressor will just occasionally fill bike tires and air mattresses, you can get a suitable product in the lower end of this range. You could even get a suitable air compressor for only $50.
If you are a mechanic, you need a powerful air compressor for automotive air tools that can support multiple pneumatic tools. A large tank coupled with a powerful motor would serve you well. A unit of this level of performance can fetch as much as $2,500, but there are models of less quality at about $500.
A roofer’s requirements tend to be less than those of a mechanic, so his/her air compressors won’t even be as powerful as the California Air Tools 10020C-22060. A compressor in the range of the Bostitch BTFP02012 pancake air compressor is excellent for roofing applications. Air compressors for this category normally start at around $100 onwards.
The California Air Tools 10020C-22060 would instead fit painting jobs where consistency is crucial. Items for this category can cost anything between $400 and $1,200. If you are lucky, you can get a powerful, low-maintenance, and quiet product for a few hundred dollars.
So, an air compressor can cost a few dollars to even thousands, but this depends on your needs. It is not surprising to find a professional surviving on a unit valued similarly to a homeowner somewhere else.
For more information on the best air compressors for particular uses, please see our buying guides & reviews:
- Best air compressors for air tools
- Best air compressors for automotive air tools
- Best air compressors for a home shop
- Best air compressors for a nail gun