[Vwdiesel] Gas Door struts

[Mark Shepherd]

      I'm still fascinated with the physics of these things How do they
seal etc?
      Could they be used in a stirling engine somehow?
      Maybe pressures not high all the time; but what is the 'liquidy'
sound I hear?
      So they are repairable!...

      http://www.strutwise.com/gasSpring.php

      Here's an extract from this site I just found:


      What is a Gas Spring & How Does it Work?
      The Basics

      A gas spring is an energy-storage device similar in function to
mechanical coil springs. Mechanical coil springs store energy by straining
the material composing the spring. A gas spring stores energy by
compressing the nitrogen gas within the gas spring. As a mechanical coil
spring is compressed, additional strain is placed within the spring, which
adds to the spring's stored energy. Likewise, as a gas spring is
compressed, the gas chamber volume is reduced due to the intrusion of the
shaft into the gas spring tube; thereby causing the gas pressure to rise,
storing more energy.

      The goal is the same with either type of spring; to move or resist
the movement of
      some object. Typically for gas springs, the object to be moved is an
automotive liftgate, hood or trunk. Gas springs are not limited to just
this use, and in fact can be used in many applications where mechanical
springs are applied.

      One of the significant differences between mechanical springs and gas
springs is the force provided at their free length. Gas springs always
require some initial force to
      begin compression. Mechanical springs have a characteristic known as
free length. This is the length of the spring with no force applied. The
force required to move the spring begins at zero and increases according to
the spring rate. Gas springs in their "free length" require some initial
force before any movement takes place. After the full initial force is
applied the gas spring will begin to compress. This force can range from 20
to 250 pounds. In mechanical springs this initial force is called pre-load
and requires additional hardware to achieve. Another significant difference
is the spring rate. Gas springs can be designed with a very low spring rate
utilizing a small package. A similar mechanical spring would require as
much as twice the package space. The ability to have a controlled rate of
extension is another major difference. Gas springs can provide a rate of
extension (controlled release of the stored energy) that can be set to a
prescribed velocity. Mechanical springs do not have this ability. In fact,
gas springs can have multiple extension rates within the same gas spring
(typically two: one
      through the majority of the extension stroke, another at the end of
the extension stroke to provide dampening).