The Lamy 2000 is a good example of a piston filling fountain pen. The ink filling system and reservoir are integrated into the pen body. To fill the pen you need to turn the knob element at the end of the body to drive a piston either up or down inside the ink reservoir. This action will either draw ink into the pen or discharge it. The threaded section of Lamy 2000 make for an easy disassembly. The nib / feed unit fits tightly into a cresent shaped opening through the section and can be pushed back out with a little force. Be mindful of where on the nib you are gripping though.  I recommend breaking the pen down in this manner for cleaning the pen thoroughly. The clutch ring can be easily lost so I recommend removing and storing in a manner to prevent this.

   With the Penatomy series of posts the idea is to dissect common filling systems to show the component parts that make up our favourite writing instruments.