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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]].
==History==
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| pages=36–37
| url=https://www.ausgrain.com.au/Back%20Issues/176magrn08/36_Spinning.pdf
| url-status=dead
| access-date=2022-07-28 | language=en-au
| archive-url=https://web.archive.org/web/20210226232835if_/http://ausgrain.com.au/Back%20Issues/176magrn08/36_Spinning.pdf
| archive-date=2021-02-26
| archive-format=PDF
| quote=[From p. 36
}}
</ref>
[[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,
Some implements employ light free-spinning protective plastic guards to enshroud the PTO shaft;<ref
| url=https://www.nsc.org/news_resources/resources/documents/power_take_off%20(pto).pdf
| url-status=dead
| access-date=2022-07-28
| date=May 2009
| publisher=National Safety Council
| at=
| language=en-us
| archive-url=https://web.archive.org/web/20140428005350if_/http://www.nsc.org/news_resources/Resources/Documents/Power_Take_Off%20(PTO).pdf
| archive-date=2014-04-28
| archive-format=PDF
}}
</ref><ref name="Privette">
{{
cite web
| url=http://www.clemson.edu/safety/pto.htm
| url-status=dead
| access-date=2022-07-29
| title=Farm Safety & Health - PTO Safety
| last=Privette
| first=Charles
| date=2002-03-01
| department=Department of Agricultural and Biological Engineering
| publisher=[[Clemson_University | Clemson University]]
| at=
| language=en-us
| archive-url=https://web.archive.org/web/20050328215328/http://www.clemson.edu/safety/pto.htm
| archive-date=2005-03-28
| quote=shields and guards were developed to prevent injury from these rotating shafts
}}
</ref>
these are mandatory in some countries. {{
Citation needed
| date=July 2022
| reason=There were 2 Citations at end of sentence. Work in neither citation mentioned mandate for PTO guards.
}}
In the UK, [[Health and Safety Executive]] guidance is contained in a leaflet.<ref name="AIS40">
{{
cite web
| url=https://www.hse.gov.uk/pubns/ais40.pdf
| url-status=live
| access-date= 2022-07-29
| title=Agriculture Information Sheet No 40 (AIS40). Power take-offs and power take-off drive shafts.
| date=October 2013
| orig-date=January 2013
| website=[[Health and Safety Executive | Health and Safety Executive UK]]
| at=
| language=en-gb
| archive-url=https://web.archive.org/web/20211031104639if_/https://www.hse.gov.uk/pubns/ais40.pdf
| archive-date=2021-10-31
| archive-format=PDF
}}
</ref>
==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>
{|class="wikitable sortable
! Type
! RPM
! Diameter
! Splines
|-
| 1
| 540
| {{convert|1+3/8|in|disp=or|abbr=on}}
| 6 straight
|-
| 2
| 1,000
| {{convert|1+3/8|in|disp=or|abbr=on}}
| 21 involute
|-
| 3
| 1,000
| {{convert|1+3/4|in|disp=or|abbr=on}}
| 20 involute<!-- The "agproud" citation references this entire table, except for Type 4 which is reffed to the ISO standard -->
|-
| 4
| 1,300
| {{convert|57.5|mm|in}}
| 22 involute
|}<ref name="agproud"/><ref name="iso"/>
Due to ever-increasing horsepower requirements from farm implements, and higher horsepower engines being installed in farm tractors, a still larger type (designated as Type 4) has been added to ISO 500. It operates at a higher rotational speed of 1300 rpm in order to allow for power transfer at reduced levels of torque. The shaft has 22 splines with a major diameter of 57.5 [[millimeters]] (mm). It is meant to handle PTO powers up to 450 [[kilowatts]] (kW), or roughly 600 [[horsepower]] (hp).
All four types rotate counterclockwise when viewed looking back from inside the tractor's cab; when standing behind 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. Newer tractors may come equipped with 540/540E and/or 1000/1000E options that allow the tractor to power certain low-power-demand implements like [[hay rake]]s or [[Tedder (machine)|tedder]]s using lower engine speeds to maintain the revolutions per minute needed, using less fuel and placing less stress on the engine – thereby improving efficiency and reducing costs.
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