Torque wrenches are very common tools these days. However, most people who use them don’t know how they work. The mechanism that torque wrenches use to control the applied torque is more complicated than it seems.
If you’re interested in knowing how these useful tools help you apply large amounts of torque with relatively little effort, you’re in the right place. In this article you’ll learn step by step how some different models of torque wrenches work.
What is Torque?
Before learning how torque wrenches work, you must first know what torque is. Torque, also known as moment of force or moment, is the vector product of the applied force by the distance from the rotation axis to the application point of the force.
So, the higher the force or distance, the higher the applied torque. Torque wrenches apply this principle to increase the amount of applied torque. Usually, the force that a person can apply with one hand isn’t enough to loosen or tighten a bolt.
Torque wrenches allow taking advantage of the strength of both arms and the additional push of both legs to increase the applied torque. Also, the length of the handle, which is the equivalent to the distance in the torque equation, also helps. The longer the handle, the higher the torque.
In the International System of Units, Torque is measured in Newton meter (N*m). In equations, torque is usually designated as M or the Greek letter tau in lower case.
Step by Step Guide of Torque Wrench Working Process
There are many types of torque wrenches and not all of them work the same way. Below, you’ll find a step-by-step explanation of how the most common torque wrenches work.
Click Torque Wrench
This type of wrench emits a characteristic click sound when reaching the maximum torque. It uses a calibrated clutch mechanism that combines the action of a spring and a ball detent. This is how it works:
- The user calibrates the maximum torque by turning a screw on the lower end of the handle.
- The screw pushes the spring.
- The spring pushes a metal ball through a hollow cylinder.
- The ball enters a socket attached to the ratchet head. In this case, the socket is a hole of smaller diameter than the ball.
- While the ball is inside the socket, the user can transmit force from the handle to the ratchet head.
- When reaching the maximum torque, the ball is compressed, pushing the spring back. Finally, the ball leaves the socket, preventing the transfer of force. At this point, the user listens to the click sound from the tool.
Slipper Torque Wrench
They use a similar mechanism to click torque wrenches. But, instead of a ball detent, slipper torque wrenches use a cam and a roller. In this case, the cam is attached to the ratchet head. This is how it works:
- The user adjusts the maximum torque by turning a screw on the lower end of the handle.
- The screw pushes the spring.
- The spring pushes the roller against the borders of the cam.
- The roller stays in place when it falls on a concave edge of the cam. At this point, the user can transfer force from the handle to the ratchet head.
- When the applied torque exceeds the resistance generated by the roller and the spring, the wrench slips, transmitting no force from the handle.
Pneumatic Torque Wrench
Pneumatic torque wrenches use a vane motor powered by air pressure to work. Air enters and exits through holes in the motor housing to generate movement. This is how pneumatic torque wrenches work:
- A compressor generates air pressure. The compressor joins to the pneumatic torque wrench with an air hose.
- Compressed air enters the engine through holes in its housing. Compressed air pushes the vanes, generating high angular speed. While the motor rotates, vanes contract and extend against the housing walls using springs.
- The air trapped between the vanes and the housing creates high pressure areas that generate sudden movements in the engine when air escapes through the output holes.
- The high angular speed is then transformed into high torque using reduction gears. This prevents wearing the bolts due to friction and controls the rotation speed of the ratchet head.
As you can see, all different torque wrenches work in a different way. Some require manual force and others use pneumatic, electric or hydraulic power. Each model can provide a different torque range. So, each one is more convenient than another for a certain purpose.
Understanding how torque wrenches work is the first step in learning how to repair your own tool. In addition, you’ll have a broader view of how to use torque wrenches for different purposes. You could even improve the concept of some existing models and develop your own design.