How to Select an Air CompressorLast updated on: March 17th, 2020 at: 09:55 am
How to Select an Air Compressor
Air compressors are essential components of many businesses. They can power a wide range of tools and are often portable and convenient. According to the U.S. Environmental Protection Agency (EPA), about 70% of all manufacturing facilities in the United States use some kind of compressed air system. But making a compressor choice among many competing models can sometimes feel overwhelming.
What are the criteria for making an informed and lasting decision when selecting an air compressor?
With all the different options available on modern air compressors, the proper selection can be a guessing game without the right set of guidelines. There are nearly as many different air compressor and option combinations as there are types of applications. Making a mistake in the selection process can cost you efficiency, extra service and even production.
Fortunately, Quincy Compressor has some answers. We’ve put together this handy air compressor selection guide to explain how air compressors work, describe a few of their specifications, discuss some elements to consider when buying an air compressor and lay out some helpful tips about how to select a compressor for your business.
How Air Compressors Work
Air compressors work like this: air pressure rises when the volume of air drops as its molecules become compressed into a tighter and tighter space. This compressed air can then be discharged to power pneumatic tools.
What causes that compression? Often, it’s reciprocating piston technology, though sometimes it involves a rotary screw, and sometimes it involves a centrifuge. A compressor with a reciprocating piston typically contains a crankshaft, a connecting rod, a cylinder, a piston and a valve head. It is powered by either a gas motor or an electric motor. An air compressor also has an air tank to hold air within a specified range of pressure. The compressor’s motor cycles on and off, as needed, to keep the tank filled with air.
One end of the cylinder sucks in air through the inlet valve as the piston moves. When the piston moves backward, the space in front of it fills with air taken in through the inlet valve, and when the piston moves forward, it compresses that air and sends it to the other end of the cylinder. At the other end of the cylinder is the discharge valve, which discharges the compressed air into the tank. As continual amounts of air fill the tank, the pressure within the tank increases even more.
How does the air compressor know when to stop compressing air? Most compressors use a pressure switch to stop the pistons automatically when the air in the tank has reached a predetermined pressure. Operators do not have to use that pressure, though — they can set the tank to a lower pressure by using a regulator. This step is important to match the air pressure in the tank with the pressure requirements of the tool the operator plans to use.
What can you do with an air compressor? You can run several different types of equipment, including grinders, drills, sanders, nail guns, spray guns and staplers. You can use an air compressor in a tire or auto shop, in manufacturing applications, in sports facilities and in many other environments. One of the major advantages of running tools via compressed air is that every tool in a shop doesn’t have to have its own motor. Instead, the single motor of the air compressor ends up powering dozens of different tools in a highly efficient process. Pneumatic tools tend to make less noise and require less maintenance than power tools as well.
How to Choose the Right Compressor Type
Before buying any pieces of equipment, there are always some key considerations to keep in mind to help guide the selection. For air compressors, these ideas can be simply stated:
- How much pressure is required?
- How much airflow is required?
- What is the air quality required?
- What is the operating duty cycle?
- What is the initial purchase price?
- What is the total cost of ownership?
- What special requirements does this application demand?
To answer the first three questions, simply determine the answer to this question: What will the compressed air be used for? The most common uses for compressed air are simply to power pneumatic tools.
In the shop capacity, the air compressor powers tools like impact wrenches, nail guns, drills, grinders and blowguns. There are hundreds of stationary and portable tools that use compressed air for their power source. Each device has manufacturer specifications for the appropriate amount of pressure (psig, bar or kPa) and airflow (cfm, l/sec or m3/min). The performance of the device is critically dependent on these factors, and these must be kept in mind when selecting an air compressor.
If the compressed air is to be used as a power source for certain precision equipment, the selection becomes even more critical. For instance, a pneumatic drill can operate with a certain maximum level of contamination that would not be acceptable for a precision dentist’s drill. Even though both drills must have the incoming air filtered to remove dust and water before entering the tool, a dentist’s drill should not receive any contamination at all, including the oil that is commonly used in operating an air compressor. Special types of compressors are available that use no lubricating fluid in the compression chamber – either oil-free or oilless.
To further clarify the compressor selection, it is important to consider the duty cycle of the equipment. Certain types of compressors are preferred for continuous duty based on their robust design and ability to run at a constant temperature, regardless of demand.
Air-cooled reciprocating (piston type) compressors are generally ideal for intermittent duty usage that requires them to operate at most 60 to 70% of the time. If the compressor is not allowed to unload, or rest, at least 30% of its operating cycle, heat could damage the head and valves.
Certain reciprocating compressors include forced lubrication, heavy-duty valves and efficient intercooling, which allow the machines to run at much higher duty cycles and still provide years of service. Rotary screw and centrifugal compressors are designed for continuous duty. Because they have internal cooling, this type of compressor can operate 24 hours a day, 365 days a year as required. This type of design, however, comes at a premium.
The “initial purchase price” of any equipment is always a deciding factor when selecting one model over another. The initial purchase price is affected by many factors, like design, pressure and flow, lubricated or oil-free (oilless) and any special features that may be required. Generally speaking, rotary screw and centrifugal compressors tend to be more expensive than reciprocating compressors because they are designed for more severe duty and longer maintenance intervals. The second part of the cost equation is the overall cost of ownership.
In general, the initial purchase price of an air compressor represents about 10% of the cost to own and operate the compressor in the first five years. The other components are installation and piping, maintenance and power. The largest contributor to the cost of ownership is power, ranging from the same cost per year as the initial investment all the way to three or four times the initial cost per year. In selecting a relatively low price up front, a customer could be paying almost twice as much for power versus a slightly higher initial cost for a more efficient compressor. To help in this part of the decision, all manufacturers of industrial equipment provide data sheets that clearly indicate the power and capacity of their standard air compressors. These data sheets can be obtained from each manufacturer or from the local distributor.
A final factor, but not the only remaining factor by any means, involves the amount of customization required for the compressor to meet the needs of the application. This can include special cooling equipment for hot or cold environments, sound attenuation devices such as enclosures or active noise cancellation, control devices to integrate into existing equipment, non-standard voltage — the list is nearly endless. If a standard piece of equipment nearly meets the requirements, it is a great advantage to make a compromise in the name of economy and long-term service.
To make this information more meaningful, consider the following table:
|Pressure Range**||Capacity Range**||Air Quality||Duty Cycle||Initial cost||5 Year Cost||Options Available|
|Reciprocating* Lubricated||0-500 psig 0-35 bar||0-125 cfm 0-60 l/sec||Low||50-75%||Low||Med High||Few|
|Reciprocating* Oil-less||0-150 psig 0-10 bar||0-100 cfm 0-48 l/sec||High||50-75%||Med||High||Few|
|Rotary Screw Lubricated||0-230 psig 0-16 bar||5-3000 cfm 0-85 m3/min||Low||100%||Med||Med Low||Many|
|Rotary Screw Oil-free||0-150 psig 0-10 bar||50-3000 cfm 1-85 m3/min||High||100%||High||Med||Many|
|Centrifugal||0-350 psig 0-24 bar||250-20000 cfm 7-560 m3/min||High||100%||High||Low||Unlimited|
The selection process should take these factors into consideration. While the above information is not meant to make a final selection, it serves to give the reader an idea of the questions to ask when dealing with the issue of equipment selection. The main purpose is to make sure the impact of a proper selection, based on real requirements like airflow, pressure and ultimate lifecycle cost, is considered rather than simple power rating and initial purchase price.
Compressor Specifications to Keep in Mind
When you’re choosing an air compressor for your business, here are a few specifications to consider as you compare different models.
What Is Cfm, and How Much Do You Need?
Cfm stands for “cubic feet per minute.” This unit is a measure of the volume of air the air compressor can produce every minute, and it determines how much power the compressor can supply to pneumatic tools. The atmosphere often plays a role in the cfm of an air compressor, since the rate at which air can flow into the inlet valve is affected by variables such as humidity, heat and wind conditions.
Knowing the cfm of your air compressor is essential for determining which kinds of tools the compressor can run.
How Much Cfm Do You Need for Air Tools?
How much cfm you need for air tools typically depends on the tool. The standard industry advice with air compressors is to overestimate your power usage by 40 to 50%. If your most heavy-duty tool requires a certain cfm, look for an air compressor that can supply 140 to 150% of that number. That way, even as the compressor ages and loses some of its capacities, you can still get your jobs done.
You don’t want to get a compressor with too much cfm, though — the EPA reports that compressed air accounts for a substantial 10% of the electricity use in manufacturing industries, so choosing a compressor that can produce enough power without guzzling your power is critical.
What Is Psi, and What Psi Air Compressor Do You Need?
Psi stands for “pounds per square inch” and provides a measurement of air pressure. This measurement is sometimes written as “psig,” which stands for “pounds per square inch gauge” and signifies that the psi is relative to the atmospheric pressure. The higher the psi, the more compressed the air within your compressor’s tank.
The right psi for your applications also depends on the tools you use. The pneumatic tools required for lighter applications such as woodworking or metalworking typically require only about 90 to 100 psi, whereas the heavy-duty tools and machinery needed in an industrial environment typically require much more than 100 psi.
Tools such as air hammers, blowguns, brad nailers, die grinders, disc sanders, hydraulic riveters, impact drivers and paint spray guns all tend to use 90 to 100 psi. Tools like tire inflators and grease guns often require 120 to 150 psi.
The chart below shows some common hand tools and the required air supply conditions to make them perform as the manufacturer states:
Buying a New Air Compressor vs. a Used Air Compressor
Should you buy a used air compressor or a new air compressor?
Buying a new air compressor means you will receive a compressor with a longer lifespan ahead of it, which is essential for preventing compressor failures that can torpedo your productivity and damage your pneumatic tools. You should buy a new air compressor if this factor is a priority for your business.
In some scenarios, buying a used air compressor can be smart as well, especially on a tight budget. Durably built air compressors can last for many years, so the right choice of used air compressor can give you plenty of years of solid use. Always work with a reliable, trustworthy dealer, though, to make sure you’re getting the best quality in a used product.
Things to Check for With Used Air Compressors
Whether you’re buying a new or used air compressor, be sure to ask questions so you know exactly what your compressor can provide.
- Previous motor use: For example, if you’re considering buying a used electrical air compressor, be certain to find out how it was formerly used. If the air compressor was plugged into an improper electrical setup, it may soon start exhibiting electrical problems as you use it. If you’re considering a used gas-powered air compressor, ask about its usage as well.
- Previous installation: Because of their portability, gas-powered air compressors often ride along to all kinds of job sites and power many dirty, rugged tools. So make sure the one you’re considering is still in good shape — check the filters and hoses for signs of wear. And if you’re considering buying a stationary air compressor, ask about its previous installation location — if it was installed in a cramped space and could not vent properly, it likely stressed its internal components whenever it ran.
- Previous patterns of use: You should also ask in what applications the previous owner operated the used air compressor — you want to ensure it was used for the right kinds of tools and jobs. If the previous owner used the compressor on jobs it was over- or underpowered for, it may have sustained damage to its engine, hoses or connection points. If an air compressor has run for too many consecutive hours, it has likely sustained excessive wear and tear as well. When you inspect the compressor, check for leaks as well, and make sure there’s no damage to the foundation or to the wheels or handle for portable models.
- Technical specifications: When you’re talking with a seller, ask about the horsepower and airflow ratings of the air compressor you have in mind. After you’ve done so, compare those numbers against the ratings given by the manufacturer. Checking these numbers lets you know the capabilities of the air compressor you’re considering and also lets you know how forthcoming the seller is.
- Service history: When you’re buying a used air compressor, it’s also essential to ask to see the service history, just as you would with a car. And if you’re buying an air compressor that requires oil lubrication, ask whether the compressor received lubrication regularly. If not, it’s not likely to function at its peak capacity.
When you’re trying to figure out whether you should buy a new or used air compressor, first determine what your priorities are. If your goal is to purchase a top-of-the-line model that will last for as many years as possible, and your budget can accommodate a new air compressor, a new machine is an excellent way to go. If you’re looking for an air compressor that can fit into a tighter budget and perform well for several years until a new compressor becomes realistic, a used air compressor can give you exactly what you need.
Single-Stage or Two-Stage
One of the critical factors to consider when selecting a compressor is whether it should be a single-stage or two-stage compressor.
Different types of air compressors work via different types of reciprocating compression cycles. The “stage” of an air compressor refers to how many times the air gets compressed. A single-stage air compressor compresses the air once, whereas a two-stage air compressor compresses the air twice. Below are a few considerations to keep in mind when you’re choosing a single-stage or two-stage air compressor.
Single-stage compressors have a single piston. In a single-stage compressor, air is sucked into the cylinder, the piston compresses the trapped air with a single stroke to about 120 psi, and then the compressed air flows into the storage tank.
Single-stage compressors are more cost-effective then two-stage air compressors, but they are also less effective in situations that require high pressures. Single-stage compressors are generally ideal for producing 120 psi or less.
Two-stage compressors are generally the best choices for industrial applications. A two-stage air compressor has two pistons to provide more air compression, and it can produce up to 150 psi or more. A two-stage air compressor is ideal for continuous use as well.
In a two-stage compressor, air is sucked into the cylinder, and one piston compresses the trapped air with a single stroke to about 120 psi, just as in a single-stage compressor. Instead of going directly to the tank, though, the compressed air flows through a cooling tube and then heads to another, smaller piston, which compresses the air to about 175 psi. After the second stroke, the air is cooled again and sent to the tank, where it is ready to produce high-pressured air for a variety of industrial equipment.
It’s important to note that the terms “single-stage” and “double-stage” refer to the number of compression cycles rather than the number of cylinders. Air compressors use two cylinders to provide the proper balance of air. In a single-stage compressor, though, both cylinders are the same size, whereas in a two-stage compressor, the second cylinder is smaller because the second piston is smaller.
Different Applications for Single-Stage and Two-Stage Compressors
Single-stage air compressors provide less air power than two-stage compressors. However, two-stage compressors usually cost more, so they may be prohibitively expensive except for large companies or shops. For a one- or two-person shop, a single-stage air compressor is generally the ideal choice. It provides quality air power at a price most smaller operations can work with.
Some common applications for single-stage air compressors include woodworking and metalwork. Woodworkers can accomplish tasks like drilling, nailing, sawing and sanding with tools that require no more than 100 psi, and metalworkers can do the same with tasks such as grinding, shearing, ratcheting and riveting.
Two-stage air compressors are ideal for applications in environments such as tire shops and industrial facilities, which tend to include many high-powered tools. One common example is car assembly and maintenance. Employees in auto plants can use two-stage air compressors to provide the high-powered air necessary for screwing, lifting, painting, greasing and more. Environments like food processing facilities and industrial factories also rely on two-stage air compressors to power heavy-duty tools and machinery along assembly and production lines.
Air Compressor Power Supply Options
Air compressors most commonly use either electrical power or gas power. Here are some factors to consider when you’re deciding what air compressor power supply to choose.
Air compressors that use electrical power are ideal if you plan to use your air compressor indoors, since they do not require a place to vent exhaust. Small electrically powered air compressors generally use typical household voltage ratings of between 110 and 120 volts. An air compressor with a powerful engine is an exception to this rule, however — an air compressor with an engine of 2 horsepower or more usually requires a 220- to 240-volt outlet. Electric air compressors are ideal in many smaller applications because they are relatively inexpensive and can work in any safe, dry area with a reliable power supply. Their power is often limited, though, and their mobility is limited by the range of the cord or extension cord.
Gas-powered air compressors are much better suited to outdoor applications than to indoor ones both because of the exhaust they vent and because their portability makes them ideal for taking from job site to job site. Gas-powered compressors often have larger engines than electrically powered compressors as well. And as long as you have gasoline, you’ll never have to look around for an outlet where you can plug your gas-powered compressor in.
One additional advantage of using gas-powered air compressors is that they offer an extensive range of shapes, sizes and tank volumes. If you plan to use a gas-powered generator, take advantage of the range of customizations available by shopping around for features like high-capacity tanks, handles, wheels and multi-valve options.
Other Factors to Consider When Selecting an Air Compressor
When you’re trying to figure out how to choose an air compressor, be sure to keep these other factors in mind as well.
Where Should You Place Your Air Compressor?
The choice of location for your air compressor is crucial because the size of many industrial air compressors makes them difficult to move. If your air compressor doesn’t have a handle and wheels, you’ll want to place it in a location that can become its permanent home. If your compressor is designed to be portable, you’ll have more options in deciding where to put it and when to move it.
The most important choice to make about the location of your air compressor is whether it will be inside or outside. As we’ve discussed above, you should generally place a gas-powered air compressor outside so it can vent its exhaust into an open area. You’ll likely want to put an electrical compressor indoors, though it will work just as well outdoors in good weather as long as it can reach a reliable power outlet.
How Much Air Do You Need?
What size air compressor do you need to run air tools? The tank capacity you will need for your air compressor depends on the volumes of air you are likely to use. If your applications have high psi demands, you’ll be much better off getting a compressor with a larger tank, even if that means a higher cost and a more cumbersome compressor to move around.
On the other hand, larger tanks typically produce short, powerful bursts of pressurized air, whereas compressors with smaller tanks are more likely to produce a steady flow of lightly pressurized air. So compressors with smaller tanks are often ideal choices for applications such as production lines, where work needs to move quickly and without interruption. They are also more affordable and easier to transport. Consider these factors whey you’re thinking about what size air compressor to buy.
If you’re wondering what size air compressor you need to sandblast, remember that the size of the air compressor should be proportional to the nozzle of the sandblaster. A sandblaster with a larger orifice will likely require a larger tank.
Consider Your Industry
Choosing the right air compressor for your industry is essential. It doesn’t make sense to use a light compressor to try to lift heavy parts in an auto shop or a huge, high powered compressor to power a single drill in a one-person carpentry shop. When you’re picking an air compressor, make sure to consider the cfm, horsepower and psi you will need for your particular set of tools and machinery.
We recommend different models of our air compressors for various industries.
- Automotive: The demands of the automotive industry make our QGS with integrated dryer option, QT and QR-25 models excellent choices.
- Dry cleaning: Dry cleaning, with its many procedures and required air pressures, makes intense demands on air compressors. We recommend our QGS, QT, QR-25 and QP models.
- Food and beverage processing: Food and beverage processing needs a supply of fresh, uncontaminated air and a compressor that can work with a variety of applications, including transferring liquids, pneumatic conveying, sprayers, presses and agitation. We recommend our QSI, QGV®️, QR-25, QT and QP models.
- Manufacturing: Manufacturing plants use air compressors all day for various tools and heavy-duty machinery, and power, durability and efficiency are essential. We recommend our QSI, QGV®️, QR-25, QT and QP models.
- Oil and natural gas: The oil and natural gas industries are demanding ones, and offshore operations mean a reliable air compressor is a necessity because quick repairs may not be an option. We recommend our QSI, QSLP (low pressure), QRNG (natural gas processing) and QR-25 models.
- Pharmaceuticals: The pharmaceutical industry requires a pristine quality of air to make safe and effective products. For this reason, we recommend our QOF oil-free scroll compressors.
- Plastics: Plastics manufacturing requires compressed air to mold, shape and finish plastic products. We recommend our QSI, QR-25, QT, QP and QVSI (vacuum) models.
- Woodworking and lumbering: The woodworking and lumber industries require efficiency, power for heavy loads and spark-free operations to reduce the risk of fire around flammable wood. We recommend our QSI, QGS, QGV®️, QR-25, QP, QT and QSVI (vacuum) models.
Contact Quincy Compressor for All Your Air Compressor Needs
Deciding to buy an air compressor is a decision that lasts a long time – the power to make the best, most informed decision is based on asking the right questions. But figuring out what to consider when picking an air compressor can be confusing. When you’re wondering how to buy an air compressor, Quincy Compressor can help. Our network of friendly, professional and knowledgeable air experts is more than happy to answer your questions and help you figure out what air compressor to buy for your business.
To find out more about the best model for your needs, contact a local Quincy dealer near you!