A torque multiplier is a tool used to provide a mechanical advantage in applying torque to turn bolts, nuts or other items designed to be actuated by application of torque, such as the actuation of valves, particularly where there are relatively high torque requirements.
Torque multipliers typically employ an epicyclic gear train having one or more stages. Each stage of gearing multiplies the torque applied. In the epicyclic gear systems, torque is applied to the input gear or ‘sun’ gear. A number of planet gears are arranged around and engaged with this sun gear, and therefore rotate. The outside casing of the multiplier, is also engaged with the planet gear teeth, but is prevented from rotating by means of a reaction arm, causing the planet gears to orbit around the sun gear. The planet gears are held in a ‘planetary’ carrier which also holds the output drive shaft, therefore as the planet gears orbit around the sun gear, the carrier and so the output shaft rotates. Without the reaction arm to prevent rotation of the outer casing, the output shaft cannot apply torque.
Along with the multiplication of torque, there is a decrease in rotational speed of the output shaft compared to the input shaft. This decrease in speed is inversely proportional to the increase in torque. For example, a torque multiplier with a rating of 3:1 will turn its output shaft with three times the torque, but at one third the speed, of the input shaft. However, due to friction and other inefficiencies in the mechanism, the output torque is slightly lower than the theoretical output.
