Air impact wrenches

Agriculture.com Staff 09/06/2007 @ 8:00am

With plenty of nuts and bolts on farm equipment to be loosened and tightened, an air impact wrench that can tackle the task with plenty of torque is a must.

A socket wrench designed to deliver high torque output with minimal exertion by the user, the impact wrench stores energy in a rotating mass, then delivers it suddenly to the output shaft. This power makes it one of the most commonly used pneumatic tools.

Impact wrenches are available in a wide range of socket wrench drive sizes (from a ¼-inch square drive to 3½-inch and larger square drives) and in several styles, including inline, butterfly, and pistol grip.

With the inline style, the tool is held like a screwdriver with the output on the end. A butterfly style is a special inline form. It has a large, flat throttle paddle on the side of the tool that can be tilted to one side or the other to control the direction of rotation rather than requiring a separate reversing control. The pistol grip user holds a handle, which is at right angles to the output.

Nick DeSimone, air tools product manager for Porter-Cable and Delta machinery, says there are four things to consider before purchasing an impact wrench: clutch, retainer, power, and ergonomics.

1. Clutch. "The two most common mechanisms are the pin clutch and the twin-hammer design. The main difference between the two is that the pin clutch takes longer to arrive at the maximum torque. For example, the longer the trigger is depressed, the higher the torque will go until you reach the maximum torque of the tool," he says.

2. Socket retainer. The two most popular retainers are the pin and friction ring (also known as hog ring). "The pin retainer has the most positive engagement," says DeSimone. "The retention of the pin design can be maximized by aligning the pin to the hole that is found in the side of the socket where it mates to the square drive of the tool. It ensures the socket doesn't come loose from the tool." The friction ring design is convenient for users who make many socket changes.

3. Power. The amount of power is measured in foot-pounds of torque. Depending on bolt size and grade, this will determine how much torque you need and which impact wrench will match your application. "Most general applications can be handled with a range of 400 to 500 foot-pounds of torque," says DeSimone.

"An impact wrench on an application uses about 60% of its torque capacity," says Larry Outtrim, national sales manager for RediPower. "This is because most impact wrenches reach 60% of maximum torque in about three to five seconds, which is the time to target for most applications."

4. Ergonomics. "These tools operate on a principal of impact to generate force. Oftentimes high vibration can be experienced," DeSimone says. Tools with an ergonomic padded grip can lessen these effects.

One of the big advantages of air tools is that they don't require their own motors. An air compressor motor converts electrical energy into kinetic energy. In addition, air tools have a higher power-to-weight ratio, which means you get a smaller, lighter tool to tackle the same job.

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