How Does Cylinder Size Affect the Damping Coefficient in a Pneumatic Damper?

[hammeraxe]

Hi, everyone!

I'm designing pneumatic damper and I need to work out what the damping coefficient is. Basically it uses a steel rod pushing in a capped aluminium tube with a small air outlet (see diagram). I'm trying to work out what the relation is between the dimensions of the cylinder and the damping coefficient. There is an instantaneous pressure build-up as force is applied to the piston, but how does this relate to damping coefficient in terms of Newton*seconds/meter? What should I look at?


http://img12.imageshack.us/img12/43/damper.png

 

[Mech_Engineer]

It's important to realize that the constant damping coefficient is a simplification for entry-level physics courses. The reality is much more complicated, especially in your damper's case because it will have a damping coeffcient which changes with speed and position.

If you know what speed the piston is moving at, you can calculate the pressure rise in the cylinder and the air escaping the hole in the end of your piston. Problem is, if your piston is moving at constant speed the interior pressure/exit flow will need be described as a differential equation.