What is a Pneumatic Torque Wrench?

Paul Scott

A pneumatic torque wrench is an air driven tool designed to apply a specific, pre-set amount of torque or tension to a fastener, typically a nut and bolt. This precise tensioning is important in many multi-fastener applications where very close tolerances need to be maintained. Unlike other forms of torque wrenches, many pneumatic torque wrenches offer a wide range of torque settings. They are also generally smaller, more powerful, and cheaper to run than electrical or manual versions.

Pneumatic torque wrenches may be used by mechanics and in industrial applications.
Pneumatic torque wrenches may be used by mechanics and in industrial applications.

The pneumatic torque wrench makes use of a compressed air source to rapidly rotate a turbine type rotor which in turn drives a shaft through a planetary reduction gearbox. This shaft is fitted with an adjustable clutch which is designed to "slip" or release at a pre-set tension. The shaft end of the pneumatic torque wrench is equipped with a fitting that allows various tools to be attached to the torque wrench depending on the application. When the pneumatic torque wrench is applied to a nut-and bolt assembly for instance, the tool will torque or tighten the nut until the pre-set tension is reached, whereupon the clutch will release and the wrench will no longer apply tension to the nut.

Many engineering applications require that fasteners be tensioned to a specific torque setting. This is particularly true of applications where several fasteners are used to equally secure two components together. The cylinder head of a car engine, for example, is usually fastened with six-to-eight stud and nut assemblies. As the cylinder head relies on a perfect fit between its lower surface and the engine block to ensure an effective gasket seal and the correct lining up of peripheral drive mechanisms, these studs have to be tensioned to exactly the same level. This precise tensioning is achieved with a torque wrench.

For various reasons, the use of compressed air to drive a pneumatic torque wrench is a common practice in those industries where such tools are used frequently. A pneumatic torque wrench is smaller and more manageable than an electrically driven model of similar capacity. For this reason, air driven tools tend to be far more powerful in reasonably sized packages than their electric counterparts such as the powered torque wrench. Pneumatic torque wrenches are also cost effective to run. This is because the generation of a compressed air source is cheaper than using electric tools. Powered or manual torque wrenches often come equipped with only a limited number of tension settings.

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