A multi-functional tool like the impact wrench (or air wrench) requires sufficient air supply to function properly. Your impact wrench may fail to work optimally if you pair it with an unsuitable air compressor. Therefore, you need to select the best, most suitable air compressor for impact wrench use. Before selecting the air compressor pump, learning a few things about the wrench in question and its performance requirements would be a good idea. Choosing the best size of air compressor for air wrenches requires intensive research because the devil is in the details.
We did the research and prepared this brief guideline that covers operating air pressure, reservoir tank, air compressor CFM and other major aspects of the air compressor configuration.
For more information on the right size air compressor for the job, please see our long form guide What Size Air Compressor Do I Need? You may also be interested in other guides in the series such as What Size Air Compressor Do I Need To Fill Car Tires?
What Is An Impact Wrench?
Torque Wrench Vs Impact Wrench
It is common for users, even experienced ones, to confuse an impact wrench with a torque wrench. An air wrench is an essential tool for doing jobs that require immense rotational torque. It is applicable for high-torque tasks such as loosening and tightening of lug nuts and fasteners. Most of the time you will find this tool the construction and automotive industries, although it is also popular in other applications where significant rotational torque is necessary.
Contrary to what many people may think, the operation of a wrench is quite straightforward. The secret behind the rotational force prowess of the tool is in its hammering principle and the pressure of airflow. This mechanism creates an incredible amount of force that forces the bolt or nut to rotate. With a good wrench and if using it correctly, there should be no nut too tight to undo.
Here is a great video showing you exactly how an impact wrench works – in slow motion! Credit to Nick Moore.
The torque wrench is different in the sense that it introduces the concept of precision and pre-calibration. Unlike the impact wrench, its focus is not on high amount of force. Of course, both tools are used for generating rotational force.
Here is a table showing the differences between the tools:
|Main feature||Low control, extremely powerful||Accurate control|
|Power source||Pneumatic or operated by electricity, battery||Manual|
|Ease of Use||Easy to use||Can cause fatigue due to long hours of use|
|Cost||Cordless impact wrenches can be relatively expensive||Affordable|
|Noise||Loud operation||Quiet operation|
As you can see so far, there are several differences between an impact wrench and a torque wrench. Looking closely, the most significant difference is the fact that one tool delivers adjustable torque while the other one doesn’t. The torque wrench typically features a torque-controlling mechanism. The means of changing this output may vary, with some varieties even using electricity.
So take note of these differences when choosing either of the tools. Go for the wrench when you are looking for high speed and force. It will screw in your nuts or remove them swiftly and with little effort. However, if your concern is specific torque on your nut, always go for a torque wrench.
How to Calculate Air Compressor Tank Size and Impact Wrench Air Requirements
Now let review some important steps for determining the best storage tank size for an air wrench. One things you need to keep in mind is that the compressor capacity determines the ability to support an impact wrench.
The most important parameters for an air compressor an air wrench are CFM, PSI, and tank size.
How to Calculate the Amount of Airflow Your Impact Wrench Needs
The CFM needed
CFM stands for Cubic Feet per Minute (CFM) and simply refers to airflow. Typically, the CFM of an air compressor should at least equal the CFM requirement for the wrench. You will only need to measure the CFM for the compressor because that of the tool is usually provided by the manufacturer.
Using a safety factor of 1.5 and with the CFM for the tool, you can get compressor CFM.
For instance, if the wrench CFM is 4CFM, the compressor CFM should be determined as shown below:
CFM is different from Standard Cubic Foot per Minute (SCFM), which may differ according to location because of its coverage of humidity, pressure, and temperature.
The PSI needed
The PSI (Pounds per Square Inch) or air pressure needed from the air compressor will also vary from one air wrench to the other. While there are some powerful impact wrenches that demand as much as 135PSI, most of these tools work at 100PSI.
The suitable air compressor needs to have pressure in excess of this to support the tool fully. Ideally, your air compressor will need to generate about 150 PSI for the best results. As usual though, we advising consulting a specialist in air compressor designs when considering investing in DIY compressors.
Tank Size needed
Now that you have determined the air requirements for the wrench, it is easier to arrive at the tank size in liters or gallons. The tank needs to be big enough to harbor that airflow. There are larger tanks as big as 80 gallons, but there are also smaller ones. The larger this capacity, the longer the air compressor will support the air tool before it can start generating more compressed air. Experts in configurations on air compressors have found an easy way of determining the ideal tank capacity for a wrench. You can simply multiply the air wrench airflow by 6 to get the capacity in liters.
In the example above, the impact wrench a CFM Rating of 4.
For the minimum tank size
6*4 gives 24 liters
It is the same as 6 gallons
A 6 gallon air compressor would be ideal for this tool.
Are You Using the tool Intermittently or Continuously?
This is a crucial question to ask yourself when determining the best size of air compressor for an air tool. You must know whether you will draw the air continuously or intermittently from the air compressor. For most tools such as a nail gun or impact wrench, intermittent use of the tool may be possible even with small or portable air compressors, but continuous use is different. The discharge capacity of the air compressor must be good enough to satisfy the air requirements of such a powerful tool.
Air Compressor Duty Cycles
An air compressor’s duty cycle is the period of time it may operate before switching to cooling mode. The duty cycle is frequently expressed as a percentage. Thermal protection is a feature on compressors that turns them off when they reach a specified temperature. If an air compressor does not have thermal protection, it is the operator’s responsibility to turn it off to avoid overheating.
Duty cycle and tank size work hand in hand; a larger tank allows the compressor pump to cool down more thoroughly, reducing the risk of wear and overheating. Not all tiny air compressors require a lot of downtime. The majority of portable air compressors recommended for use with impact guns can run continuously for medium to long periods of time.
Ideal Air Compressor Size For Different Size Impact Wrenches:
The ideal air compressor for a particular tool depends on the size of the latter. If the wrench is larger, it will demand a larger air compressor. Since there is no exact guide that cuts across all pneumatic tools, we chose to cover the most common sizes of wrenches. Below we have given an estimate of airflow needed for each common size of impact wrench:
- ¼ Inch Impact Wrench
This is probably the smallest wrench you will find in the market. If you already have one and are wondering what size of air compressor is the best, here is the main point: this tool won’t demand a lot. As long as the air compressor can provide about 1.5CFM -2CFM, the tool should work perfectly. Consider an option such as the 6-gallon air compressor from Dewalt. It delivers 2.6 CFM @ 90 PSI and works quietly. You can easily get other air compressors with similar or close characteristics.
- ½ Inch Impact Wrench
This size of wrench is very popular. As you can guess, this is because they are at the center of the chart. For this reason, the compressor options for these tools tend to be more. If your air compressor has CFM rating is about 3-5cfm, you can comfortably pair it with this type of wrench. From experience, air compressors with ratings around 5CFM perform the best for this tool. One of the best air compressors in this category is the DEWALT Air Compressor, 225-PSI Max, Hand Carry with Wheels, 4-1/2 Gallon (D55146).
- ¾ Inch Impact Wrench
The ¾ inch impact wrench is rare to find, but it has its applications, especially in professional applications. For this wrench, you need higher power than in the ½ inch impact wrench. Therefore, look for air compressors with airflow rating of about 7cfm. You could go lower, but the results would not be as desirable.
- 1 Inch Impact Wrench
You have one of the biggest air wrenches if you have this one. It is ideal for bigger jobs found in places like construction sites and large garages. Because this is a massive tool, it will need an equally good air compressor to operate excellently. You are talking about an air compressor with as much as 10CFM. Because of this high rating and the other qualities that go hand in hand, this item is bound to be more expensive than the smaller sizes.
Here’s a table summarizing the recommended air compressor airflow and pressure for these tools:
Impact wrench size (inch)
|Airflow (CFM)||Pressure (PSI)|
Will a pancake air compressor run an impact wrench?
Yes, a pancake size air compressor can run an impact wrench, but it has to be powerful enough. An impact wrench is a powerful tool that requires substantial amount of air pressure and airflow (CFM) to work correctly. If you are asking will a pancake air compressor run a wrench, you need to compare the parameters of the two.
A pancake air compressor can run an impact wrench if it can deliver at least 1CFM. This is the smallest rating you will mostly see in the smallest of these tools. Pancake air compressors such as the BOSTITCH Pancake Air Compressor, Oil-Free, 6 Gallon, 150 PSI and the PORTER-CABLE Air Compressor, 6-Gallon, Pancake, Oil-Free easily meet these requirements.
This article has given us a lot of insight into how the impact wrench works. It is a highly effective tool for handling sizeable bolts and lug nuts. We have discovered the importance of airflow and other factors that characterize the ideal air compressor for impact wrenches. Now you have an idea which compressor to use with the tool to achieve the best results.
The ideal air compressor for an air wrench has sufficient power to offer enough pressure to unlock even the toughest lug nut. A product like the Makita MAC5200 air compressor features a lot in impact wrench jobs. However, you can always analyze the products on offer using this guide and in line with your needs. You should also check customer reviews online to see what other users are saying about the air compressor for not only tire inflation, but also how it works for a brad nailer, nail gun and other tools.