How Does An Impact Wrench Work

Air Impact Wrench

Practically every repair or tire shop in the world has at least one, most likely multiple impact wrenches. They are virtually indispensable for removing stubborn nuts and bolts on vehicles, heavy machinery, and equipment. Although various impact guns have differing operation and controls, we’ll attempt to explain the basics of how a common impact wrench works.

History of the Impact Tool

First a little history, an impact wrench is a power tool that is commonly used for removal and installation of bolts. The impact tool was patented Aug. 27, 1935, by Robert H. Pott of Evansville, Indiana. (United States Patent No. 2012916).

Pott’s design incorporated a revolutionary design that utilized stored energy in a spring-loaded rotating mass and clutch assembly to hammer and rotate in a pulsating manner. This novel design was able to easily loosen large frozen nuts and bolts on heavy equipment that previously would have required a cutting torch to remove.

The Ingersoll-Rand company purchased the rights to the impact tool and began manufacturing impact wrenches. Ingersoll Rand continues to this day to produce an entire line of electric and pneumatic impact wrenches which are sold globally.

What Makes the Impact Hammer Effect?

A rotating mass is accelerated in a hammer mechanism. The hammer is then quickly connected to the output drive shaft creating a rotating hammering effect. The hammer then disengages and spins freely before repeating the process. As long as there is sufficient tightness on the fastener the impact tool continues to hammer and rotate. Once the fastener has loosened the tool is designed to stop hammering and spin freely to quickly remove or install the nut or bolt.

How an Impact Wrench Works Video

Here is a good video demonstrating the internal operation of an impact wrench in operation.

Impact Wrench Manufacturers

Currently there are dozens of companies manufacturing air impact tools. Here is a list of some of the most common.

  • ACDelco
  • AirCat
  • Campbell Hausfeld
  • Chicago Pneumatic
  • Ingersoll Rand
  • Mac Tools
  • Matco
  • Proto
  • Snap-on
  • Speedair

In addition to the companies listed above, many major cordless tool manufacturers also produce cordless impact wrenches.

  • Bosch
  • Craftsman
  • DeWalt
  • Makita
  • Metabo
  • Milwaukee
  • Porter Cable
  • Ryobi
  • Wen

How Do You Use an Impact Wrench?

Impact wrenches are extremely easy to operate. Most are shaped like a pistol gun with a trigger and have a reversing switch. You simply attach a properly sized impact socket on the end of the gun and place it on the nut or bolt you want to install or remove. Most often the tool is used for removing stubbornly tight or rusted fasteners. When you pull the trigger, the anvil begins a rotating and hammering motion. This usually quickly breaks the fastener loose and spins it out. The trigger or other control typically regulates the torque (twisting force) applied, allowing for adjustment depending on the current task.

What Sizes Do Impact Wrenches Come In?

Impact wrenches come in various sizes, from small quarter inch drive models to massive two-and-a-half-inch drive models, with half inch drive impact guns being the most common size. Many models have an extended anvil to make it easier to remove fasteners from deep locations such as truck and heavy equipment tire rims.

What Types of Power Do Impact Wrenches Use?

Impact guns can use various methods to power the tool.

  • Pneumatic (Air Powered)
  • Electric (AC Corded)
  • Electric (DC Rechargeable)
  • Hydraulic (Oil Powered)

The compressed air pneumatic powered impact wrenches are the most common for repair shops and industrial settings. These guns are typically exceptionally durable and provide a high torque to weight ratio.

120-volt AC impact tools and various voltage cordless DC powered impact wrenches are popular for portability and don’t require a separate air compressor, however most can’t match the nut busting reverse torque of the pneumatic impact guns.

Where Can I Buy an Impact Gun?

There are dozens of places to buy Impact tools. Most tool distributors such as MAC, Snap-On, etc. carry the more expensive commercial models. Big box home improvement stores like Home Depot and Lowes carry a selection of air and electric powered impact tools. Online distributors, Amazon being the most popular and usually the best value carries many types and models. You can compare and directly link to the most popular half inch air impact wrenches here.

Quick Tips:  

1. Use short, large diameter air hoses  and high-flow air couplings for maximum power.

2. Put both hands on the impact wrench for better results removing stubborn nuts.

3. Just snug wheel lug nuts with impact , then use torque wrench to tighten to specifications.

The Bottom Line

Commercial repair and tire shops already know the utility and money saving benefits of impact tools. I can tell you from experience, if you do any type of vehicle maintenance or even need to change a tire now and then, an impact gun will make your life a lot easier. Instead of busting your knuckles or throwing out your back stomping on a lug wrench, a few quick pulls of an impact wrench and those lug nuts are off. Whether you need a cordless battery powered model, or a powerful air powered impact gun will depend on your needs. Personally, I own both. You can check current prices of Impact guns by clicking the green button below. Impact Wrenches

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