Liquid and air displacement

simonrepro

I am trying to re-manufacture an ink cartridge and need to understand the phsics of how this thing is working.

The Cartridge

1. Ink in tube
2. Ball bearing on top of cartridge which I can push into the cartridge to allow me to get liquid in to clean
3. Adaptor on top of cartridge which links through to an expandible plastic bag inside the cartridge, the bag fills up with air when I blow in the top adaptor. This adaptor is not 100% air tight so the air can slowly come out of the bag through the adaptor.
4. 520 45micron nozzles on bottom of cartridge which spray out ink.

I fill the cartridge with ink by removing (2.) then attaching a syringe to (1.) then as I blow into (3.) this allows the syringe to be pushed to enter ink into the cartridge but it inflates the air bag on the end of (3.).

What I need to be able to do:
Fill the cartridge with ink, then put some force on the ink to force the ink into the bottom nozzles, this is called priming. After doing this I then need to be able to deflate the plastic blow up bag leaving normal atmospheric pressure within the cartridge, there must be no air in the cartridge and it must be completely filled with ink.

My Problem:
If I blow in the bag and pump ink in, when I deflate the bag it pushes the ink back into the syringe.

Can anyone help with this please?