Technical Standardization
Agricultural PTOs are standardized in dimensions and speed. The ISO standard for PTOs is ISO 500, which as of the 2004 edition was split into three parts:
- ISO 500-1 General specifications, safety requirements, dimensions for master shield and clearance zone
- ISO 500-2 Narrow-track tractors, dimensions for master shield and clearance zone)
- ISO 500-3 Main PTO dimensions and spline dimensions, location of PTO.
The original type 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 types, 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. A 10 spline type was used with some early equipment such as the 1948 Land Rover, a six spline adapter was usually supplied. It is customary for agricultural machines manufacturers to provide the nominal PTO power specification, an indication of the available instantaneous power at the shaft.
Read more about this topic: Power Take-off
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