A power wrench is any wrench that uses something other than human power to function. There are three main types of power wrenches—electric wrenches, air wrenches and impact wrenches. These three wrenches all work in a similar fashion; they just use different methods and motivating forces for power. In addition to the three standard types, several other power tools have socket attachments that effectively turn them into a power wrench. This is especially common in the basic electric tools like drills and screwdrivers.
There are many types of wrenches. The type most often converted into a power wrench is called a socket wrench. These wrenches have a series of removable sockets that fit on the end of the tool. Each of these sockets consists of two parts; the end that fits on the tool, which is always shaped the same way, and the part that fits over the nut or bolt. That end comes in multiple sizes and shapes, each designed to fit on a different-sized hardware piece.
Electric wrenches are the most common form of household power wrench. These wrenches are little more than an electric motor connected to a shaft. The user pulls a trigger or presses a button, and the shaft turns. These wrenches have very little power when compared to other forms of power wrenches, but they are inexpensive to produce.
There are many types of powered non-wrenches that may be converted into an electric power wrench. In many cases, home power tools that rely on the spinning shaft system will have adapters that turn one tool into another. For instance, an electric screwdriver may have an adapter that allows it to accept standard wrench sockets. This is mostly a money-saving feature for the consumer, as nearly all spinning shaft household tools use a similar interior design.
Air wrenches are the step up from a standard electric wrench. These wrenches use compressed air to generate motive force, but otherwise work nearly the same as an electric wrench. They are generally of much heavier construction, allowing them to generate significantly more torque.
The impact wrench is the most powerful of the standard power wrenches. These tools may have any number of different power sources, including electricity, compressed air or hydraulic systems. These wrenches store power in a coil that is disconnected from the driveshaft when not transferring power.
When the user activates the wrench, the coil connects and transfers a huge burst of energy. The coil then disengages, and a standard system takes over. This means that the operator only feels a brief tug, even though a huge amount of force was transferred. Generally, a user will operate an impact wrench in short pulses to maximize the power sent to the shaft.