Now that you have decided to get an air compressor for your air tools like Impact wrench, Nail gun, Paint gun; the most important question that you might be facing is “What size compressor do I need?”. Well, let’s get right into it and see how you can make a correct decision.
The simple answer to your question is to get a compressor which matches or has a greater CFM than the rated CFM of your tools.
But this is not entirely true. There are a lot of other factors to consider before you select a compressor for your tools. I will make a list of the things to consider, so that you can make a good decision.
As we know, there are a lot of advantages of using air tools over electric tools. Air tools offer better power to weight ratio, longer run time before they need maintenance, they run much cooler than electric tools, they are lighter, they are cheaper when compared to electric tools and they are much more efficient.
There are disadvantages to air tools as well. First of all they need compressed air to produce work. This means you would need some kind of a setup where you would have a tank or a reservoir with compressed air.
So, lets try and find out how to select the correct size compressor for you.
5 Things to consider before sizing an air compressor
1. What kind of tools would you be using – CFM rating?
This would directly impact your decision regarding the size of the compressor you would need. If you intend to just fill some air in a tire, fill up an inflatable swimming pool or do some light spray painting, then a 3 gallon portable air compressor should be the right choice for you. But, if you plan on doing some DIY stuff with a couple of your friends or you plan to do some medium to heavy work in the garage, then you will need to go with a larger 30 to 60 gallon.
The question also boils down to the CFM rating of your compressor.
What is CFM?
CFM stands for cubic feet per minute. It is the volume of free air that the suction side of the compressor intakes from the atmosphere. To make it simple, it the the volume of air that the compressor puts out into the storage tank or the air reservoir.
Every air tool that you use is rated to operate at a specific CFM and a specific PSI. PSI or pounds per square inch is the pressure of the compressed air that your tools operate at. Most of the air tools nowadays are rated to operate at 90 PSI. Also, most of the compressors are able to produce 90 PSI of pressure.
So before you decide on buying a compressor, the first thing you need to do is find out the rated CFM of all the air tools you are going to use.
Lets say you are planning on using a Framing nailer, a reversible pneumatic drill and a 1/2″ impact wrench.
The CFM of these tools would be :
Framing nailer – 2.5 CFM (average)
Reversible pneumatic drill – 5.0 CFM (average)
1/2″ impact wrench – 6.0 CFM (average)
Here the tool which is drawing the most CFM is the 1/2″ Impact wrench.
So, you would need a compressor which has a rated CFM of at least 50% more than the CFM drawn by your largest pneumatic tools.
In the above case you would need a compressor of atleast 6.0 x 1.5 = 9.0 CFM.
As a rule of thumb, I would suggest you to go to about 1.5 times the maximum CFM so than you can get your work done without any interruptions.
Here is a chart of CFM drawn by some common Air tools. Remember, most of the air tools are rated to work at 90 PSI. This is an industry standard. So we can skip the PSI as any new compressor would be able to develop more than 90 PSI.
|Air Tools||Average CFM at 90 PSI|
|Reversible Pneumatic Drill||5|
|Impact wrench – 1/2″||6|
|Impact Wrench – 3/8″||4|
|Impact Wrench – 1″||10-12|
|Spray Paint Gun||5–10|
|Air Hammer/ Chisel||4|
|Orbital Body Sander||10-12|
|Cut Off Tool||6|
|Impact Driver 1″||10-12|
|Impact Driver 3/4″||6-8|
2. What size air tank would you need?
Now that we know the CFM rating of the compressor we need, the next task is to select the appropriate tank size. Size of the air tank determines the volume of compressed air that can be stored at a particular pressure (PSI)
Larger tanks would accommodate a larger volume of compressed air, hence you would be able to run your tools for a longer time before your compressor cuts-in. If you aim to do small jobs like inflating a tire, then a 3 gallon tank should just be fine. If you plan on using an impact wrench, then it is better to go for a bigger tank size (30 to 60 gallons). This would ensure that you finish your job before the compressor starts again. Frequent cutting in would lead to the compressor running hot, the lube oil consumption will increase and also the compressor valves would need frequent maintenance. So, its better to select the optimum size of air tank.
3. Should you buy a portable or a stationary compressor?
Lets talk about portable compressors first. As the name suggests, they are portable. Being that, they are smaller and easy to move about in your place of work. The down side to these are that their capacity is less. What that means is, you might not be power to use your air tools continuously for a long time. Also, they might not produce the required torque for your tools.
These compressors usually have a wheeled base and are easy to move around. Some pan-cake type compressors, usually in the 3 to 6 gallon air tank range can be easily carried around. Do not expect to get a lot of work done using these smaller compressors. They will be suitable for some small DIY work, tire inflating. If you plan on using your compressor occasionally and if you do not want go for a less expensive solution, then get a portable compressor. Additionally, these compressors can be connected to a 120 Volts socket, which you can find almost everywhere.
Now, on the other hand stationary compressors cannot be moved around. They are heavy-duty and have a larger tank which means it will hold up a huge volume of air. If you plan on working in your garage over the weekend with your friends or if you would like to do some heavy-duty work like sand blasting or plasma cutting, then these are the compressors you should choose. They have a compressor of greater capacity which means it will churn out air at a greater CFM and PSI. They downside to stationary compressors is that they will occupy some floor space and would pretty much stay in that place, since they cannot be moved around easily.
There is another consideration of the pipeline required for the compressed air to be delivered from the air tank o your place of work, this adds up to extra cost. Also, since these compressors use a bigger pump (more Horse Power), you will have to connect them to a 230 Volts socket. These cannot be connected to 120 Volts socket as it will either trip the breaker or burn the wiring. If you consider cost, they cost much more than the portable compressors. But if you do not mind spending extra bucks, and if you want the “biggest and the baddest” compressors, then go for the stationary compressor.
I personally like the portable ones, as they pretty much get the job done. Lets face it, most of the time we would end up doing small jobs which really do not need a stationary compressor.
4. Should you go for an Oil filled or an Oil free compressor?
Oil free compressors implies that the compressor pump runs without any lubricating oil. An oil free compressor can be either a reciprocating type (piston type) or a screw type compressor. Since there is no lubricating oil, they tend to run much hotter than their counterparts. In addition to cooling, the lubricating oil carries away most of the tiny dirt particles which get sucked into the compressor. There is a higher chance of the sealing rings, piston and the liner getting damaged due to particles coming in. Also, these compressors tend to make a lot of noise when they operate. You will need to keep them is such an area where the noise gets muffled or else you will have angry neighbors.
One more thing you would need to consider when going for an oil free compressor is the cooling. Make sure there is an adequate amount of air flow so that the compressor gets cooled and does not run very hot. Generally the oil free compressors do not last long and they would need much more maintenance than the oil filled compressors. One of the reasons you should consider buying them is if you will not be using the compressor very often or if you are on a budget.
On the other hand, Oil filled compressors have lubricating oil in their crank case. This oil gets circulated via a small attached pump, or is splashed to the cylinder by the connecting rod. Here the oil makes sure that the compressor runs a lot less hot and also makes a very little noise. These compressors cost more than the oil free ones, but they would last much longer. If, you are planning to use your compressor for a long time then this would be your best option. They run much cooler and hence they have fewer breakdowns and maintenance issues when compared to oil less compressors.
Some disadvantages are that, you will need to top up the lube oil regularly. This depends on the amount of usage. Either your compressor would have a dip stick or a sight glass to check the level of lube oil present. It is a good idea to completely change the lube oil in your compressor once a year. These would definitely be a good choice in the long run and you will get your money’s worth!
5. Considering Horse Power and Duty cycle of your compressor
Horse power and duty cycle also play an important role when you choose your air compressor. Let us discuss about horse power first. Horse power of a compressor motor is the energy that it draws from your power socket. As a rule of thumb, for domestic usage stick to a compressor below 4 Horse Power. Also for every horse power the equivalent CFM produced is about 3 -4 . So, if you have a 4 Horse power compressor, it would produce about 12 CFM at a particular PSI (usually 90 PSI).
Duty cycle is another important factor you need to consider. Basically what duty cycle means is the amount of rest period a compressor needs before. Every compressor is rated to a particular duty cycle. Suppose a compressor is rated for 50% duty cycle in a 1 hr cycle, what that means is : The compressor should rest for 30 minutes after operating for 30 minutes. In the same way, if the duty cycle is 100% : The compressor would be able to run continuously for 1 hour before it needs to cool down. This does not mean that you will not be able to run the compressor beyond its duty period. It will get very hot and is just not good for the compressor.
So, what is the conclusion?
Now that you know what to look in a compressor, make a list of all the specifications you would be needing.
- CFM rating that you would need. Keep a 50% margin.
- Make sure you have an idea of appropriate Air tank size you would need.
- Narrow down to whether you need a Portable or a Stationary Compressor.
- Consider which one suits you, Oil filled or Oil free compressor.
- Lastly, check the Duty cycle and the Horse power of the Compressor you like.
I hope you consider all these points before making a decision. Additionally, do some more research on your own which would help you decide better. Thank you for taking the time to read this post and I really hope it helps you out.