Torque wrenches are used to apply a correct torque (force) to a ‘critical part’. Often we’d like to apply the correct torque in order to:
- Avoiding over-tightening the parts(s). Over-tightening could lead to damage of the parts: small delicate parts could break, threads could be stripped, bodies could crack…
- Avoid under-tightening the part(s). Under-tightening could lead to: parts being able to be loosened by hand, parts vibrating loose…
When using torque wrenches with adapters (e.g. the use of a crowfoot wrench), one has to be careful as to apply the correct torque in order avoid over torqueing parts. There are some situations in which we’ll have to ‘adjust’ the torque value. Let’s have a closer look:
In the drawing below the part to be torqued is indicated by the thick black circle. As you can see, the center of the part is directly below the center of the torque wrenches’ ratchet mechanism. As long as those centers are directly above each other, the torque value the wrench is set at will be applied to the part being torqued. In other words, no adjustments have to be made.
Often the center of the part to be torqued is not directly in line with the center of the torque wrenches’ ratchet mechanism. This situation occurs because some kind of adapter is used. In the drawing below the part to be torqued is indicated by the thick black circle. It can be clearly seen that the centers do not line up. This being the case, the torque being applied to the part would be greater than the value being set on the torque wrench.
In this situation, the following question arises: “to which value do we have to set our torque wrench to in order to apply the correct torque”. The answer can be derived by use of the formula below.
Example: what is the value we have to set the torque wrench to if we wish to apply a torque of 30 Nm to the part with the value for L being 40 cm and the value for A being 5 cm? Using the formula, the torque wrench has to be set at 26.666 Nm. Note that this value is clearly less than 30 Nm.
The center to center distance (A) for our tools:
It goes without saying that for the same torque wrench being used, the longer the adapter length, the smaller the value we have to set the torque wrench to, in order to obtain the same torque on the part.
If we apply a certain torque by means of a torque wrench to a part using a torque adapter, we could ask ourselves: “what torque the part is being subjected to”. To answer this question, we can derive a modified formula from the above one.
Example: if we set the torque wrench to 30 Nm with the value for L being 40 cm and the value for A being 5 cm, the torque being applied to the part is 33.75 Nm. Because of the torque adapter this value is greater than 30 Nm.
If the torque adapter is used at a 90 degree angle, no corrections have to be made. In the drawing below the part to be torqued is indicated by the thick black circle.
We only recommend to use torque adapters either directly in-line with or at 90 degrees to the torque wrench.
Nothing contained in these notes or shall be construed to over-ride or replace the relevant standards or manufacturer’s recommendations, manuals, data or product specific training. The contents are believed to be correct to the best of our knowledge and are offered in good faith. No warranty is expressed or implied. The author, Scuba Clinic Co., Ltd. accept no liability for any loss, damage or injury however caused resulting from information contained in these notes. It is the responsibility of the reader to verify the correct information, practises and procedures prior to commencing work.