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An Easy Guide to Choosing an Air Compressor

Choosing an air compressor

Choosing An Air Compressor

Picking out the right compressor for your application is a pretty simple process, right? Well if you know anything about compressors you know that choosing an air compressor is not that simple. Finding the right compressor is an intensive process, there is no one size fits all answer, and I wish there was. You have to make sure your air has the right flow, the pressure isn’t too far off in either direction, you have the power to run the machine, and many other things that are integral to the process of making high-quality compressed air. Don’t let this overwhelm you when it comes to picking out your compressor, that is what this guide is for.

The information needed to adequately size your air compressor is all important, but some things need to be addressed first. The most crucial ones to pay attention to are:

  • CFM (Cubic Feet per Minute)
  • Pressure (PSI/PSIG)
  • Space

By being able to identify the flow rate, pressure, space and air needs will lead you in the right direction of figuring out just what kind of machine you need. CFM is typically determined by the horsepower of the air end, so if you know your CFM you will have an idea of what horsepower you need to be running at and vice versa. Knowing these factors will greatly limit your options to make sure you are getting the best compressor for your application. After you know these things, you can focus a little more on the details of your compressor:

  • Type of Compressor
  • Technology
  • Power
  • Utilization
  • Storage
  • Noise
  • Industry Air Standards

These elements of selecting a compressor come second not due to their importance, but instead are second as they do not help reduce your options, but instead are often extra variables that need to be considered before purchasing. Variables like storage, industry air standards, and noise can be corrected through additional components being added on to the compressor, however, others like utilization, technology, and the type of compressor need to be addressed prior to purchasing a compressor.

By following along with this guide, you will be able to not only go through the process of picking your compressor yourself, but also know why those factors are important to consider. Outside of CFM, PSI, and Available Space, there is no particular order for these steps to be followed in and the variables can be determined however is easiest. The most important part is being able to identify and find the information you need.

 

Let’s Size a Compressor

 

CFM and Air Flow

What exactly is CFM and the flow of compressed air? Well CFM is the volume of air that can be compressed by the pump in one minute: a high CFM rating means a compressor can provide more air, which indicates that the bigger your operation the more CFM you are going to need.If you have a preexisting system, it is pretty easy to identify your system’s output and how that air is being used. If you have a bunch of air being wasted, there may be a bigger problem than getting a lower powered air compressor.

If you don’t have a pre existing system and are looking to make one, we can help you figure out what your expected CFM requirements would be. All this involves is taking inventory of your equipment, or expected equipment and note how much air is required for them to operate properly. Most hand held tools need between 30-40 CFM, while more industrial equipment can need 90-100 CFM to operate correctly. Once you have taken note of everything that needs compressed air, you should then figure out what CFM is required for operation.

To get those measurements you need to see what the tools are rated for, and then determine how long they are on a duty cycle. If it is only running a quarter of the time, 15 seconds of every minute it is running and if it is on a continuous cycle it is running every second of that minute so it would be using 4 times more air. Most tools are rated for the 25% duty cycle, so if you are going to be using the tool continuously, you will need to multiply the CFM by 4 to understand how much air you are actually using.

If you are wanting to ensure that your tools are not cutting it close when it comes to having enough CFM. You want the ability to be variable based on needs and going a little larger than needed will give you that buffer room. For all of your tools, take the CFM based on duty cycle and then add 50% of the total to it. For example, if your tools were rated for 5 CFM, you would want a compressor with a capacity for at least 7.5 CFM at your desired PSI.

 

Pressure and Horsepower

We’ve mentioned Pressure and PSI a few times now and these are the measurements for how much air is being compressed into a given space. It is a measurement of the air pressure delivered by your compressor. The higher the PSI gets, the more the air is compressed and with that increased pressure you can store more air in the tank. It is important to find the balance with your pressure so that you can maximize storage but still not waste energy and potentially damage your tools by having your air under excess pressure.

By understanding your maximum operating pressure, you can determine what type of compressor you need. If you don’t have a high maximum pressure, most compressors will work for you, but if you need high pressure air, you may want to consider looking into a two stage compressor where the air goes through the process of compression twice. The main point is to make sure that the PSI rating of your compressor is rated for at least your highest rated tool. This means if you have multiple tools and the highest is rated for 100 PSI, your compressor should have a pressure rating of at least 100 PSI.

Horsepower is very similar to both CFM and Pressure in being an important variable to be aware of. Horsepower is often tied to the CFM of a compressor. As it typically goes the higher the horsepower the higher the CFM, and the greater the pressure of that compressor the slower it will go. So a 10HP compressor that operates at 100 PSI will have a higher CFM than the same air end operating under 150 PSI. If horsepower is important to you, go ahead and use it as a measurement to find your compressor. If you already have a specific horsepower in mind it will greatly help limit your options.

 

Available Space

Although it may seem self explanatory, more goes into the placement of equipment than meets the eye. Compressors need enough space to fit comfortably without sacrificing the quantity of air intake. Most compressors fit comfortably with one side up against the wall, but it is important to look and see the type of space you personally have available. If you need the power but are lacking in space for a horizontal tank, vertical tank mounted compressors might work for you. Just because you have limited space does not mean you need to sacrifice storage or power.

Being aware of the space that you have can be extremely beneficial to picking the right compressor. If you know you don’t have space for a horizontal tank you’ll need to look for a vertically mounted tank. Maybe you have the space but you need a dryer, you could do a full feature system with a dryer included that is mounted on a horizontal tank, or use that space for a vertically mounted unit with a dryer next to it. Point being, that if you know the space you have for the compressor it will be much easier to decide on the compressor you like and it can even impact the styles you are looking for.

 

The Nitty Gritty of Your Compressor

Now that you have a basic understanding of what you are looking for in a compressor, we can get into the details about what you really want. Now if you are looking for a smaller personal use and don’t feel like this information applies to you, you already have all the information you need to find a good fit for you, but there may be a few things that sneak up on you. We still have not covered some variables that you may need to be on the lookout for.

Now if you are still here and interested, this is when you really get to decide the benefits of your machine, the little pieces and components you might not have noticed that will end up saving you time and money in the long run. A lot of the components and pieces that may be considered additional can do wonders for your peace of mind and system longevity. Compressors aren’t a cheap investment so you should consider all of your options before you make a buying decision. So let’s go through the different options and variations you may want to consider.

 

Type of Compressor

Picking the style of compressor you need can be dependent upon a few things: the amount of utilization, duty cycle, quantity and quality of air needed. Each air end has strengths and weaknesses depending on the application. If you have a low duty cycle a reciprocating compressor would work for you but if you have a nearly continuous duty cycle you would want to go with a rotary screw compressor. This makes it hard to pick one based on how it compresses or the energy efficiency alone.

 

Reciprocating Piston

The reciprocating piston compressor is the most commonly used compressor as it is the cheaper option in terms of compressors. They are an industry staple due to their longevity and broad applications. When run properly, one of these machines can last anywhere from 15-20 years.These compressors operate in a manner identical to internal combustion engines- you know the ones that power most of our cars- except instead of the energy from combustion being pushed through, compressed air is the byproduct.

As the crankshaft rotates the piston moves in and out of the compression cylinder. While the piston moves up, the air in the cylinder is compressed down and then moved onto stage 2. As the piston is moving back to its original position it pulls more air into the pocket to then be compressed on the next rotation. The air flow is directly determined by the size and speed of the pistons.

 

Rotary Screw

The rotary screw has become the go to for the auto industry and any industry that requires high quantities of compressed air for extended periods of time. With two intermeshing screws, consisting of one male and one female rotating screws. The air enters and is squeezed between these two helically opposed screws. As these screws rotate, the volume of space that the air is in is decreased and the byproduct of this is compressed air.

These compressors are designed to run duty cycles of 80-100% and therefore are the favorites for manufacturers and auto shops that need consistent supplies of air to keep them going. They are typically a little more upfront but they make up for this in their energy-efficiency and long lifespan operating on long intervals.

 

Scroll

The scroll compressor is the face of oil-free air. It operates in a similar manner to the rotary screw except rather than rotors it is a set of scrolls. One scroll is stagnant as the other rotates around in a circular motion to compress the air as it moves along and the pocket of space shrinks forcing the air into a continuously smaller space until it is released at the desired pressure.

As the moving scroll rotates around, it comes nearly into contact with the stagnant scroll but never quite touches it. This makes the rotary scroll the quietest and the cleanest of the bunch. These types of compressors are often used in places like dentists and doctor’s offices to power their tools with air clean enough to be used in a person’s mouth.

If you are still unsure about what type of air end you would want, or are just wanting to learn more about the basics of compressed air before you buy,  feel free to check out this post to learn more.

 

Technology

When it comes to technology, it can be attributed to a broad set of additional features or enhancements on the compressors. Technology can be anything from having an upgraded control panel, to the motor operating at variable speeds to account for demand. These features are included on some of the newer models and series but not on the older ones. The big impact this will have on your compressor is up front costs and peace-of-mind later. Adding additional technologies will often increase the initial price of the compressor but it also will be the best version available on the market.

These additional features can be beneficial in the long run but are also not completely necessary. If you don’t have a need for a Variable Speed Drive Rotary screw because you are only using 20 CFM at a 25% duty cycle. That type of investment would not make sense, but if you are in charge of an auto body and shop then you would consider making such an investment. The same thing can be said for all the other additional technology available: oil-free, upgraded display, energy efficiency, etc.

Each one has its own perks and benefits to your system, but it comes at a cost and you want to make sure you aren’t overpaying for your compressor. When it comes to deciding on additional technology make sure you compare the pros to the additional costs, it would be a shame to overpay for something that you do not need. The most common technology out there at the moment is the Variable Speed Drive or the VSD. This breakthrough in rotary screw technology lets the machine run at different rates depending on the demand.

Most compressors are either on and running or off with no in between. VSDs have access to that in between so that less energy is being consumed to produce the air. If demand is high, the compressor will be running at 100%, but then once it diminishes the rate of compression will follow suit. This allows the compressor to fulfill demand without using as much energy as a fixed-speed rotary screw. It also minimizes energy spikes needed to get the compressor going. The initial investment is returned very quickly as these compressors can cut energy costs anywhere from 40-60%.

 

Power

An overlooked but incredibly important factor is the power source you have available for your compressor. A few potential thoughts come to mind as to what you might want to consider when it comes to your power source:

  •  Is it single or three phase power?
  • Does it run at a specific voltage?
  • How many amps is your breaker rated for?
  • Will you need to upgrade your power in order to get a compressor that fits your needs?
  • Will you be using a power source other than electricity?

These questions can help guide you through what you need to be thinking about with your compressor. Getting the power to line up is critical because if you don’t have enough power available the compressor will not run. If you have three phase power, you are in luck because even the machines rated for single phase can attach a converter to make it work on three phase.

Power is all about making sure you have enough to properly get your compressor running and keep it running. It won’t take long, but a simple check on how many amps you can put out and the type of power the building has can go a long way with your compressor and making sure you get what you need.

Now you may be wanting to move your compressor around or don’t have consistent electricity where you work and that is okay, there are diesel powered air compressors for those jobs. The same rules apply just with less information needed. If you are going to be using one of these you need to have enough fuel to keep the compressor running when you need it. (With the prices of everything though you would be better off going with electricity, if possible.)

 

Utilization

Just how often are you running your air compressor? Is it all day everyday? Do needs vary depending on time of day? These questions are all important to consider because utilization is the key to determining just what type of compressor you need. It is important to be aware of your individual usage so you can identify when you might be wasting energy as well.

When it comes to utilization and compressors, a simple rule to follow is:

  • Less than 4 Hours a Day: Reciprocating Compressor
  • Between 4 and 8 Hours a Day: Belt Driven Rotary Screw
  • 8 hours and more a Day: Direct Drive Rotary Screw

If you are worried about bordering on a usage threshold, it would never hurt to go the size up to give you that extra clearance just in case something were to happen. If you need a scroll for your application this information does not directly apply, this should be used to help determine whether a rotary screw or reciprocating piston will be more beneficial to your operation and your wallet.

 

Storage

The process of creating compressed air is very energy intensive and you want to make sure you have enough on standby for whenever you need to use your tools. Having that backup air means even if your compressor goes down you will have air power for a little bit while you try to get it back up and running. The problem comes with trying to make sure you have enough backup air storage. A quick rule of thumb for picking storage is you should have 3-5 gallons of storage for every CFM of air you have. If you are rated for 50 CFM you should have around 150-250 gallons of storage.

Although storage is important, you can build a compressed air system that does not have one; however, it is not recommended to do so. Having that storage is your safety net and not having one is taking a risk that could otherwise be avoided. The tank is not responsible for making the air, it just means you have more time between duty cycles. You can never have too much storage but you can definitely not have enough.

 

Noise

When most people think of a compressor they imagine a machine so loud you can’t hear yourself think when you are around it. Sadly, that is the reality of a piston compressor running at full load, but it does not have to be your reality. Most compressors come standard with vibration pads to help reduce the noise of the machine. Now you may be in a dentist’s office or using your compressor indoors and have it nearby, if this is you there are plenty of options you can choose to limit that noise.

Scrolls are without a doubt the quietest model you can go with. They are both oil-less and make no contact internally to avoid the process of making noise during compression. These compressors are also equipped with the technology needed to reduce noise even more. If you don’t need a scroll but are looking for a quieter compressor you will want to look into ones with enclosures, noise dampeners, and other materials to dampen the sound. Some of the more modern technologies like VSD, VFD, and other speed variations contribute to noise reduction with their changes in speed.

 

Industry Air Standards

Air quality is incredibly industry dependent. Someone who is using the compressor in their garage would not be held to the same quality standards as someone who is using their compressed air to paint cars in an auto and body shop. That auto shop might also be held to a standard that is lower than someone who is using their compressor in a dental office.

If you are working in industry, your best bet is going to be an oil-injected compressor. The oil is used for lubrication, sealing, and cooling in the air compressor. This would be a great option if you have your own workshop as well. If you are in food or medicine on the other hand, it goes without saying that you need an oil-free compressor. Your product can have an adverse affect or even harm your customers if any quantity of oil is found in the air.

If you are not sure where you need to be, the ISO 8573-1:2010 Standard is your best friend. It lists out the air quality classes and gives the specifications for the quantity of specific particulates, water, and oil. As long as you are meeting those standards you will be doing just fine. If you need to increase the quality of your air, you will want to look into proper filtration for your compressed air system.

 

Before You Buy

Well, now there is nothing left for you to learn. Take the knowledge that you have gathered to go out and buy your own compressor. Now, if it still seems intimidating, no need to fret, we have trained customer service representatives waiting by the phones to answer your questions. All it takes is a quick call.

If talking on the phone isn’t your speed and you would rather do more research yourself, go ahead and check out Warthog University to learn more about Compressed Air.

 

Learn More From the Source

Atlas Copco

Quincy Compressors

 

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