Experimental power take-offs were tried as early as 1878, but International Harvester Company (IHC) was first (in 1918) to install a PTO on a production tractor. In 1920, IHC offered this option on their 15-30 tractor, and it was the first pto-equipped tractor to be submitted for a Nebraska Test. The first PTO standard was adopted by ASAE (American Society of Agricultural Engineers) in April 1927. The PTO rotational speed was specified as 536 ± 10 rpm; The direction was clockwise. The speed was later changed to 540 RPM.[3]
In 1945, Cockshutt Farm Equipment Ltd. of Brantford, Ontario, Canada, introduced the Cockshutt Model 30 tractor with Live Power Take Off (LPTO). LPTO allows control of the PTO rotation independently of the tractor motion. This was an advantage when the load driven by the PTO required the tractor motion to slow or stop running to allow the PTO driven equipment to catch up. In modern tractors, LPTO is often controlled by push-button or selector switch. This increases safety of operators who need to get close to the PTO shaft.[4] [edit] 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), and 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.
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