Power take-off

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A power take-off (PTO) is a splined driveshaft, usually on a tractor or truck that can be used to provide power to an attachment or separate machine. It is designed to be easily connected and disconnected. The power take-off allows implements to draw energy from the tractor's engine.

Safety

The PTO and its associated shafts and universal joints are a common cause of accidents and injury in farming and industry. The according to the National Safety Council, 6 percent of tractor related fatalities in 1997 in the USA involved the PTO. When a piece of clothing, which can be as small as a single thread, touches a spinning part it can be pulled around the part. The clothing and the person wearing it are pulled into the shaft often resulting in loss of limb or death. Some implements do use plastic guards to try to keep a person from becoming entangled in a PTO shaft, but even with guards people need to exercise caution around PTO shafts when they are plugged into a tractor. In some countries it is illegal to operate a PTO without the shaft guard correctly fastened. ^[1][2]

Technical

Agricultural PTOs are standardized in dimensions and speed. The original specification calls for operation at 540 revolutions per minute (RPM). A shaft that rotates at 540 rpm has 6 splines on it, and a diameter of 1⅜". Two newer specifications, supporting higher power applications, operate at 1000 RPM and differ in shaft size. The larger shaft has 20 splines (1¾" diameter), while the smaller has 21 (1⅜" diameter). All three types rotate counterclockwise when viewed from the tractor. It is customary for agricultural machines manufacturers to provide the nominal PTO HP specification, which stands for the available instantaneous power at the shaft. The value of the PTO HP is also given in watts.

References