Power take-off

Power take-off

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A power take-off or power takeoff (PTO) is a spline
Rotating spline
Splines are ridges or teethon a drive shaft that mesh with grooves in a mating piece and transfer torque to it, maintaining the angular correspondence between them....

d driveshaft
Driveshaft
A drive shaft, driveshaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement...

, usually on a tractor
Tractor
A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...

 or truck
Truck
A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

, 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.

History


Experimental power take-offs were tried as early as 1878, and various homemade versions arose over the subsequent decades, but International Harvester
International Harvester
International Harvester Company was a United States agricultural machinery, construction equipment, vehicle, commercial truck, and household and commercial products manufacturer. In 1902, J.P...

 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
American Society of Agricultural and Biological Engineers
The American Society of Agricultural and Biological Engineers , was founded in 1907 and is based in St. Joseph, Michigan. It is an international engineering society with about 9000 members in over 100 countries...

) in April 1927. The PTO rotational speed was specified as 536 ± 10 rpm
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...

; 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
Cockshutt Plow Company
Cockshutt was a large tractor and machinery manufacturer based in Brantford, Ontario, Canada.Originally founded as the Brantford Plow Works by James G. Cockshutt in 1877, the name was changed to the Cockshutt Plow Company when it was incorporated in 1882. After James died shortly thereafter, his...

 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.

Safety


The PTO and its associated shafts and universal joint
Universal joint
A universal joint, universal coupling, U joint, Cardan joint, Hardy-Spicer joint, or Hooke's joint is a joint or coupling in a rigid rod that allows the rod to 'bend' in any direction, and is commonly used in shafts that transmit rotary motion...

s are a common cause of incidents and injury
Injury
-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...

 in farming and industry. According to the National Safety Council
National Safety Council
The National Safety Council is a 501 nonprofit, nongovernmental public service organization dedicated to protecting life and promoting health. Headquartered in Itasca, Illinois, NSC is a member organization, founded in 1913 and granted a congressional charter in 1953...

, 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
Mark Fidrych
Mark Steven Fidrych , nicknamed "The Bird", was a Major League Baseball pitcher. He pitched his entire career for the Detroit Tigers ....

 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. In the UK, Health and Safety Executive
Health and Safety Executive
The Health and Safety Executive is a non-departmental public body in the United Kingdom. It is the body responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare, and for research into occupational risks in England and Wales and Scotland...

 guidance is contained within leaflet AS24(rev1)

Technical standardization


Agricultural PTOs are standardized
Standardization
Standardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....

 in dimensions and speed. The ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 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
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...

 (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.

Commercial vehicle PTOs



Truck transmissions have one or more locations which allow for a PTO to be mounted. The PTO must be purchased separately and care is required to match the physical interface of the transmission with a compatible PTO. PTO suppliers will usually require details of the make, model and even serial number of the transmission. Care is also needed to ensure that the physical space around the transmission allows for installation of the PTO. The PTO is engaged/disengaged using the main transmission clutch and a remote control mechanism which operates on the PTO itself. Typically an air valve is used to engage the PTO, but a mechanical linkage, electric or hydraulic mechanism are also options.

Units will be rated according to the continuous and intermittent torque that can be applied through them and different models will offer different "PTO shaft rotation to engine RPM" ratios.

In the majority of cases, the PTO will connect directly to a hydraulic pump
Hydraulic pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic.Hydrostatic pumps are positive displacement pumps while hydrodynamic pumps can be fixed displacement pumps, in which the displacement cannot be adjusted, or variable displacement pumps, which have a more...

. This allows for transmission of mechanical force through the hydraulic fluid system to any location around the vehicle where a hydraulic motor will convert it back into rotary or linear mechanical force. Typical applications include:
  • Running a water pump on a fire engine or water truck
  • Powering a blower system used to move dry materials such as cement
  • Raising and lowering a dump truck bed
  • Operating the mechanical arm on a bucket truck used by electrical maintenance personnel or Cable TV maintenance crews
  • Operating a winch on a tow truck
  • Operating the compactor on a garbage truck
  • Operating a Hiab/Grapple truck

It is also possible but less common to connect something other than a hydraulic pump directly to the PTO.

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