Welcome To P8ntballer.com
The Home Of European Paintball
Sign Up & Join In

How do Shim Stacks work?


"I am Become Death, squeegier of Worlds"
Oct 10, 2011
Middle of bloody Nowhere
So, I recently got myself a PMI low pressure kit to drop my tank's output pressure from 800 to 450ish PSI - which, as I was switching the shims out, got me thinking:

How do Shim Stacks regulate pressure? For an example, I removed 10 curved (I think its a belville stack) shims from my regulator, then installed 12, slightly thinner (1.125mm versus 1.4mm) shims.

Now, in theory, this will drop the output pressure from 800 PSI to 450ish PSI. I have no idea how that works.

Can anyone with some knowledge of pneumatics enlighten me please?


Nov 27, 2006
The shims form a spring

When the regulators pin valve is opened the bottles pressure of 3000psi or 4500psi is released
The shims from a spring that resist closing a valve. When there is enough pressure forward of the shims pressing back the shim spring closes the valve and locks the 3000/4500psi in the cylinder

The original shim combination is a stronger spring that will be pushed back at 800psi
Your low pressure adjustment weakens the shim spring and it is push closed at 450psi

When empty the fill nipple rattles loose. When there is any air pressure in the cylinder it tries to escape any way it can and presses the fill nipples valve shut
Attach to a fill station and if the compressor / source has more pressure than the cylinder then it blows the nipple valve open and fills the cylinder until they equalise.
The fill nipple valve could be in any position (and stays open) as the pressures are equalised
Stop filling and purge the fill hose and the cylinders pressure blows the nipple valve shut
Last edited: