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{{short description|Methods for transmitting power from a source to an application}}
[[File:Zapfwelle eines Traktors - power take-off of a tractor.jpg|thumb|A PTO at the rear end of a farm [[tractor]]
[[File:A Tractor's rear.jpg|thumb|A PTO (in the box at the bottom) in
A '''power take-off''' or '''power takeoff''' ('''PTO''') is one of several methods for taking power from a power source, such as a running [[engine]], and [[power transmission#Mechanical power|transmitting]] it to an application such as an attached implement or separate machine.
Most commonly, it is a [[spline (mechanical)|splined]] [[drive shaft]] installed on a [[tractor]] or [[truck]] allowing implements with mating fittings to be powered directly by the engine.
Semi-permanently mounted power take-offs can also be found on industrial and marine engines. These applications typically use a drive shaft and [[bolted joint]] to transmit power to a secondary implement or accessory. In the case of a marine application, such as 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]]. Jet aircraft have four types of PTO units: internal gearbox, external gearbox, radial drive shaft, and bleed air, which are used to power engine accessories. In some cases, aircraft power take-off systems also provide for putting power ''into'' the engine during engine start.<ref name="X29PTO">NASA Technical Memorandum 101731; Monitoring Techniques for "X-29A Aircraft's High Speed Rotating Power Takeoff Shaft"; David F Voracek, Ames Research Center, Dryden Flight Research Facility, Edwards, California, December 1990 [http://www.nasa.gov/centers/dryden/pdf/88209main_H-1680.pdf nasa.gov]</ref> See also [[Coffman starter]].
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[[International Harvester]] Company (IHC) was first to market with a PTO on a production tractor, with its model 8-16, introduced in 1918.<ref name="PrippsMorland1993pp37-39">{{Harvnb|Pripps|Morland|1993|pp=37–39}}.</ref> 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.<ref name="PrippsMorland1993pp37-39"/> He and his IHC colleagues incorporated the idea into the 8-16, and designed a family of implements to take advantage of the feature. IHC was not alone in the market for long, as within a year PTOs were appearing on other production tractors, such as some [[Case Corporation|Case]] models. In 1920, IHC offered the PTO option on their 15-30 tractor, and it was the first PTO-equipped tractor to be submitted for a [[Tractor#Nebraska tractor tests|Nebraska tractor test]]. The PTO was a competitive advantage for IHC in the 1920s, and other companies eventually caught up with PTO implementation.
Inside the [[transmission (mechanics)|transmission]], the exact point along the [[gear train]] where the power is taken off determines whether the PTO can be run independently of vehicle travel ([[ground speed]]). Early PTOs were often taken off the main output shaft, meaning that the vehicle had to be "in gear" in order to run the PTO. Later this was improved by so-called live PTO (LPTO) designs, which allow control of the PTO rotation independently of the tractor motion. This is an advantage when the load driven by the PTO requires the tractor motion to slow or stop running to allow the PTO driven equipment to catch up. It also allows operations where the tractor remains parked, such as silo-filling or unloading a [[manure spreader]] to a pile or lagoon rather than across a field. In 1945, [[Cockshutt Plow Company|Cockshutt Farm Equipment Ltd]] of [[Brantford]], Ontario, Canada, introduced the Cockshutt Model 30 tractor with LPTO.
==Safety==
[[File:TractorPTOshaftMay04.jpg|thumb|Protective plastic sheath enshrouding a PTO shaft]]
The PTO, as well as its associated shafts and [[universal joint]]s, are a common cause of incidents and injury in farming and industry. According to the [[National Safety Council]], six percent of tractor related fatalities in 1997 in the United States involved the PTO. Incidents can occur when loose clothing is pulled into the shaft, often resulting in [[bone fracture]]s, [[Amputation|loss of limbs]], other permanent disabilities, or death to its wearer. On April 13, 2009, former [[Major League Baseball]] star [[Mark Fidrych]] [[Mark Fidrych#Death|died as a result of a PTO related accident]]; "He appeared to have been working on his truck when his clothes became tangled in the truck's power take-off shaft", District Attorney Joseph Early Jr. said in a statement.<ref name=espn-fidrych>{{cite web|title=Examiner: Fidrych suffocated to death|url=http://sports.espn.go.com/mlb/news/story?id=4073519|work=ESPN.com|access-date=7 January 2014|date=16 April 2009}}</ref> Despite much work to reduce the frequency and severity of agricultural injuries, these events still occur.<ref>{{Cite journal|last1=Tinc|first1=Pamela J.|last2=Sorensen|first2=Julie A.|date=2019-01-02|title=Marketing Farm Safety: Using Principles of Influence to Increase PTO Shielding|journal=Journal of Agromedicine|volume=24|issue=1|pages=101–109|doi=10.1080/1059924X.2018.1539421|issn=1059-924X|pmc=6353692|pmid=30346257}}</ref>
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==Technical standardization==
Agricultural PTOs are [[Standardization|standardized]] in dimensions and speed. The [[International Organization for Standardization|ISO]] standard for PTOs is ''ISO 500'',<ref name="iso"/> 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 (designated as Type 1) calls for operation at 540 [[revolutions per minute]] (rpm). A shaft that rotates at 540 rpm has six splines on it, and a diameter of {{convert|1+3/8|in}}.<ref name="agproud">{{cite web | url=https://www.agproud.com/articles/32127-equipment-hub-understanding-power-takeoff-drivelines | title=Equipment Hub: Understanding power takeoff drivelines - Progressive Forage | Ag Proud }}</ref>
Two newer types, supporting higher power applications, operate at 1000 rpm and differ in shaft size.<ref name="agproud"/> Farmers typically differentiate these two types by calling them "large 1000" or "small 1000" as compared to the Type 1 which is commonly referred to as the "540". All new types (2, 3, and 4) use [[involute]] splines, whereas Type 1 uses straight splines.<ref name="iso">{{Cite web |last=International Standard |date=April 1, 2014 |title=Agricultural tractors - Rear-mounted power take-off types 1, 2, 3 and 4 |url=https://cdn.standards.iteh.ai/samples/56698/4acca3e1ee5246fa8218c17d65da045f/ISO-500-1-2014.pdf |access-date=September 29, 2023 |website=International Standard}}</ref>
Inch-denominated shafts are round, rectangular, square, or splined; metric shafts are star, bell, or [[American football|football]]-shaped.<ref name="tulsa">{{cite web | url=https://www.driveshaftsoftulsa.com/blogs/news/the-different-types-of-pto-shafts | title=The Different Types of PTO Shafts | date=15 February 2021 }}</ref>
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