Air Cylinders 101

What is an air cylinder?  It is a metal tube, sealed at both ends, with a rod and plunger inside.  When  air is introduced into an air port, the rod and plunger gets pushed up or down, according to where the air port is located.   The length at which the rod gets pushed out is referred to as stroke length.   Below are some diagrams on how two types of cylinders work.

                

This a diagram of  a single action air cylinder.
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This diagram represents a simplified description of a double action air cylinder.
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This next diagram represents the double action air cylinder used in a pop up head application.  The weight of the head or prop resets the rod to the bottom of the cylinder.





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Frightprops.com has a page on air cylinders here

What is a Grave jumper/ Pop Up Head?

A pop up head is a head or skull that is mounted on an air cylinder.   If I'm correct, a grave jumper is a head or skull pop up that comes from behind a gravestone.  That may be a simple description, but some grave jumpers are heads , shoulders, and some have arms attached.  In 2011  the wonderful Passport to Dreams & New blog had a post on the history of the pop up heads in the Haunted Mansion.