By Grainger Editorial Staff 10/23/23
Impact wrenches can save you the strain when loosening and tightening high-torque nuts and bolts. Instead of relying on your own muscle power, an impact wrench uses a powerful spinning hammer to generate hundreds of high-torque impacts every second. Most impact wrenches are capable of spinning at over 1,000 RPM and applying hundreds of pounds of torque, making quick work of jobs like removing wheel lug nuts or assembling heavy equipment.
Impact wrenches can be powered by either compressed air or an electric motor. Both types work in essentially the same way — instead of applying torque directly to the tool’s socket driver, an impact wrench’s motor spins a drum-shaped hammer inside its housing at high speed. With each rotation, this hammer strikes the socket drive shaft, which is why an impact wrench’s driver is called an anvil. The impact transfers the hammer’s momentum, instantaneously applying hundreds or even thousands of foot-pounds of torque to the tool head with minimal exertion from the operator.
If the hammer’s initial impact fails to turn the bolt, it will slide past the anvil and make another rotation, gathering momentum for the next impact. So instead of binding like a direct-drive electric drill, the impact wrench will continue to hammer against a stuck bolt without twisting away from the operator’s grip.
In the past, only pneumatic pressure could deliver the explosive power required by an impact wrench. But today, cordless impact wrenches with lithium-ion batteries and brushless motors can take on even heavy-duty jobs. Which type of tool is right for you will depend on how you intend to use it.
Pneumatic impact wrenches have some advantages over battery-powered wrenches. First, heavy-duty pneumatic wrenches produce more torque. Some larger 1-inch-drive models have 2-3,000 foot pounds of breakaway torque. The most powerful pneumatic wrenches can deliver 5,900 foot pounds of breakaway torque, far surpassing the strongest battery-powered wrenches. If you’re working on equipment with large sockets, corroded bolts or high-torque values, a pneumatic wrench may be your only option.
A pneumatic wrench’s second advantage is endurance. Since the wrench is powered by an air compressor that can run continuously, the air supply will replenish while you’re moving between bolts. Unlike a battery-powered impact wrench, a pneumatic wrench coupled to an appropriately sized compressor will never need to stop work because it’s out of power.
Some mechanics also prefer the ergonomics of pneumatic impact wrenches, which tend to be quieter, vibrate less and typically weigh less than similarly powered cordless wrenches. If you’re doing a big job with dozens of nuts to tighten, an air-powered tool may be less fatiguing.
A pneumatic wrench’s biggest drawback is that it must be attached to an air compressor. Air hoses can create a tripping hazard in the shop, and the tool's reach will be limited to a hose length from the pneumatic connection point, such as a your compressor or output port. If you don’t already have an air compressor, buying one will be an added expense. On the other hand, if you are already set up with a compressor and have air hoses running to your work station, a pneumatic impact wrench can be run from the same power source as a host of powerful pneumatic tools like grinders, chisels, sanders and paint guns.
Cordless impact wrenches are powered by rechargeable batteries, making it easy to bring the tool to job sites beyond the reach of an air hose. They are ideal for mobile mechanics, since the wrench can be packed in a toolbox with the rest of your gear.
A battery-powered tool can’t match the strength of the biggest pneumatic wrenches, but plenty of cordless wrenches are capable of turning a one-inch drive and applying over 1,000 pounds of breakaway torque to the anvil. That should be plenty of power for common tasks like loosening lug nuts and replacing lawnmower blades.
A cordless impact wrench will also save the expense, space and noise of an air compressor. Instead of a bulky air tank and a loud compressor, the battery powered tool only requires a compact charging station. Cordless wrenches also eliminate the need for air hoses that can create trip hazards and snag on equipment when working in tight spaces.
There are also corded electric impact wrenches, which draw power directly from an electrical outlet. They have the advantage of operating continuously without the need to recharge, as well as eliminating the need for an air compressor. However, corded wrenches offer less torque than many cordless wrenches, and they lack the mobility and portability of a battery-powered wrench.
When picking an impact wrench, remember that there is considerable overlap between the capabilities of pneumatic and cordless wrenches. Most jobs can be accomplished with either type. The work environment and personal preference will determine which wrench is right for your shop.
Get more tips and insight on choosing the right tool for the job here.
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The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.