Editing Rack and pinion (section)

{{short description|Type of linear actuator}}
{{for|rack-and-pinion railways|Rack railway}}
[[Image:Rack and pinion animation.gif|frame|right|Animation of a rack and pinion]]

<span lang="my">A</span> '''rack and pinion''' is a type of [[linear actuator]] that comprises a circular [[gear]] (the ''[[pinion]]'') engaging a linear gear (the ''rack'').<ref name="agma">{{cite book|isbn=1-55589-846-7|oclc=65562739|title=Gear Nomenclature, Definition of Terms with Symbols|pages=72|id=ANSI/AGMA 1012-G05|publisher=[[American Gear Manufacturers Association]]|year=2005}}</ref> Together, they convert between rotational motion and linear motion: rotating the pinion causes the rack to be driven in a line. Conversely, moving the rack linearly will cause the pinion to rotate. 

The rack and pinion mechanism is used in [[rack railway]]s, where the pinion mounted on a [[locomotive]] or a [[railroad car]] engages a rack usually placed between the rails, and helps to move the [[train]] up a steep [[Grade (slope)|gradient]].  It is also used in [[arbor press]]es and [[drill press]]es, where the pinion is connected to a [[lever]] and displaces a  vertical rack (the '''ram''').  In [[pipeline transport|pipelines]] and other industrial piping systems, a rack displaced by a [[actuator|linear actuator]] turns a pinion to open or close a [[valve]]. [[Stairlifts]], [[lock gate]]s, [[electric gate]]s, and the mechanical [[steering]] mechanism of cars are other notable applications. 

The term "rack and pinion" may be used also when the rack is not straight but '''arcuate''' (bent), namely just a section of a large gear.<ref>{{cite book | last = Phillips | first = Jack | title = General Spatial Involute Gearing | publisher = Springer Berlin Heidelberg | location = Berlin, Heidelberg | year = 2003 | isbn = 3662053020 }}</ref>

A single pinion can simultaneously drive two racks, parallel but opposite; which will always be displaced by the same distance, only in opposite directions.  Conversely, by applying opposite forces to the two racks one can obtain pure torque on the pinion, without any force component.  This '''double rack and pinion''' mechanism can be used, for example, with a pair of [[actuator#Pneumatic|pneumatic actuator]]s to operate a [[valve]] with minimum stress.<ref>{{cite web|title=Automax SuperNova Series Pneumatic Rack & Pinion Actuators|url=http://www.flowserve.com/files/Files/Literature/ProductLiterature/FlowControl/Automax/AXENBR1001.pdf|publisher=Flowserve Corporation|access-date=7 July 2014}}</ref>