Epson 33 / 33XL Cartridge Anatomy and Refilling

Most older cartridges have strange airways and passages in them. In some ways perhaps to justify filling cartridges half full. New Epson cartridges are smaller and they do seem to have a more straightforward construction.

It is possible to carefully cut open an Epson cartridge without damaging it. One side of the cartridge is airtight and this is the side which is opened in picture below. The other side simply has another wall under it.

As can be seen easily, the cartridge has a single main chamber. There is a tight canal where the ink outlet is.

The air inlet port is very tight. The cartridge is able to keep vacuum inside. It looks like the inside volume of the cartridge is designed to shrink as the ink is used. The metal plate in middle and the spring under it ensures that inside the cartridge is always negative pressure so the ink will not flow out.

If the inside volume nears zero. The metal plate presses to a lever which opens the air inlet port in corner until it gets in some air so the negative pressure will not rise beyond a level.

I have found out that the cartridge keeps negative pressure even if it has no liquids. There must be some mechanism or membrane at the ink outlet which does not allow air or liquids to travel towards inside the cartridge.

As can be seen below, cartridge keeps the foil completely pressed in with very little volume left inside. It does NOT replenish missing content with air. The air intake valve does not allow air intake even though the spring inside the cartridge is creating negative pressure.

Refilling Epson 33 / 33XL Cartridge

Unknown to most, the green cartridge caps do not make an airtight seal around the outlet port.

The cap will tighten the bottom of the cartridge perfectly. However the little pipe in front of the cartridge outlet is connected to the inside of the cartridge.

As can be seen clearly, the pipe is connected to space between the side wall and transparent foil. The side wall has a labyrinth and a hole to outside. The labyrinth is probably to keep the dust outside. I also found out that some cartridge walls are not completely sealed at factory as I have seen them leak at arbitrary points!

This means that you can't simply make a hole anywhere on the cartridge for filling. As even with the green cap installed, the cartridge will start leaking to inside immediately as there will be no negative pressure holding the ink. The ink will flow out from the outlet and enter to the pipe. It will then travel between the transparent plastic piece and the black wall with air hole.

Before I found out about this, I have drilled few cartridges from the top and tried to fill them. The result was that the ink eventually started coming out from the side wall hole. In some cartridges the wall was not totally sealed so it started seeping through the

Refilling Option 1

As the ink will flow out from cartridge if the negative pressure is stopped. We may only fill the cartridge from bottom. The only suitable place I found for this purpose is the prism eyelet.

You must drill the eyelet very carefully as it is only 2mm away from the plastic foil. I found out that eyelet gets drilled very quickly so do not apply any pressure to the drill.

Yes, the plug covers the eyelet hole but printer simply will think that there is ink. It is possible to put the flap other way around also. I felt little resistance first but cutting the little part of the wall solved the issue. Perhaps you may find smaller plugs also.

Even the ink must obey the laws of gravity. So it won't be leaking out from the output port when it is the highest point.

However, when plugging the hole, you must squeeze the cartridge from sides to expel as much air as possible. This way once you release the cartridge, there will be little negative pressure built inside it.

Refilling Option 2

So you prefer having a hole on top? That is also possible. As usual, you need to drill very carefully as within 2mm distance is the transparent plastic cover. Just use patience and do not press the drill down at all. Let it slowly form the hole.

As the air pressure balance pipe in the outlet is the problem. We can simply block it so the ink won't be able to flow down when the inside negative pressure is lost. You can simply put a small piece of silicone sealant using a toothpick to the hole.

Yes, it would perhaps be possible to re-open the hole after filling using a needle. But what happens if we don't? Perhaps ink flows more rapidly down due to negative pressure built when it is used by the ink head? I have left the hole plugged and did not see any negative consequences yet. Actually, none of the chinese cartridges have such hole either. I am not sure what worst can happen.

Then you need to make the hole in the middle of the cartridge where the other side is connected to top solidly.

Once the green cap is on, the ink will not be able to flow down due to pressure build up at the outlet. However, you still need to squeeze cartridge when inserting the plug. So once you relese it, there will be slight negative pressure built inside the cartridge. Without any negative pressure, cartridge may leak until pressure is balanced, once the green cap is removed.

One thing to consider is that in this position the plug interferes with the metal plate inside the cartridge. However it is probably not a problem. This can be seen in my very first picture which I took from the side of the cartridge.