Help and Support Centre - What is a PTO?

 

 

 

A power take-off or power takeoff (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.

Semi-permanently mounted power take-offs can also be found on industrial and marine engines. These applications typically use a Cardan shaft and bolted joint to transmit power to a secondary implement or accessory. In the case of a marine application, such shafts may be used to power fire pumps. In aircraft applications, such an accessory drive may be used in conjunction with a Constant Speed Drive.

 

 

Experimental power take-offs were tried as early as 1878, and various homemade versions arose over the subsequent decades, but International Harvester Company (IHC) was first to install a PTO on a production tractor, with its model 8-16, introduced in 1918. Edward A. Johnston, an IHC engineer, had been impressed by a homemade PTO that he saw in France about a decade before, improvised by a French farmer and mechanic surnamed Gougis. He and his IHC colleagues incorporated the idea into the 8-16, and designed a family of implements to take advantage of the feature. 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 tractor test. The first PTO standard was adopted by ASAE (the 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. The PTO was a competitive advantage for IHC in the 1920s, and other companies eventually caught up with PTO implementation.

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.

 

 

The PTO and its associated shafts and universal joints are a common cause of incidents and injury in farming and industry. 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. On April 13, 2009 former Major League Baseball star Mark Fidrych died as a result of a PTO related accident; "He appeared to have been working on the truck when his clothes became tangled in the truck's power takeoff shaft," District Attorney Joseph Early Jr. said in a statement.

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 or truck . In some countries it is illegal to operate a PTO without the shaft guard correctly fastened.

 

 

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 (1" 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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