====== Double barrel ======
{{wst>image_cl|Patek Philippe|Ref. 5101P|Patek Philippe Ref. 5101P "10 Day Tourbillon" with **double barrel** and 10 days power reserve|210px}}

A **double barrel** (or even **triple barrel** or **four barrel**) [[movement]] or watch features more than one [[mainspring]] and [[barrel]] for increased [[power reserve]].

As watches became more complicated with the advent of the [[chronograph]], [[repeater]], and other [[complication]]s, the need arose for larger [[power reserve]]. Since a mainspring can only hold so much energy, watchmakers began adding a second [[barrel]] and [[mainspring]]. Today, some watch movements even include three or four barrels to power their complications or give longer running time.

Multiple barrels can be configured in three different ways 

  * The barrels can be linked **in parallel**, driving the same [[gear train]] and providing extra [[torque]] for a movement's complications as well as longer [[power reserve]]; for example, the [[Vacheron Constantin Patrimony Traditionnelle 14-day Tourbillon]] has two sets of two stacked barrels all unwinding together.
  * The barrels can be set up **serially**, driving a single gear train with longer [[power reserve]], as in the [[Longines]] [[L890]] of [[1975]].
  * The barrels can also be set up to drive **multiple gear trains**; for example, the [[JLC 380]] in the [[Jaeger-LeCoultre Duomètre à Chronographe]] uses one barrel and gear train for the time movement and another separate barrel and gear train for the chronograph functions.

===== See also =====
  * [[Long power reserve]]
  * [[Jaeger-LeCoultre Duomètre]]
  * {{tagpage>Double_barrel_movements|Double barrel movements}}
  * {{tagpage>Triple_barrel_movements|Triple barrel movements}}
  * {{tagpage>Four_barrel_movements|Four barrel movements}}

===== Literature =====
  *[[Das große Uhrenlexikon]]; Author [[Fritz von Osterhausen]]; ISBN 3898804305


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