 Welcome to BCH Technologies. This video is a part of video 1 of our twin chamber refill series. If you want to see the whole video, please visit the link below. A twin chamber cartridge is divided into two chambers. The back chamber is designed as an ink reservoir. The front chamber is filled with sponges. The sponge regulates the ink flow to the outlet on the bottom. The two chambers are divided by a wall. For non-axial cartridges, such as a regular cartridge or startup cartridge, the wall is sealed on the bottom. Therefore, the ink cannot flow to the front chamber. The back chamber is never used. If you can find a way to make a hole in the bottom of this wall, you will make an axial cartridge. On the top, there is a T-shaped air intake, which leads to a long air channel. The air channel connects to an air hole. When a cartridge is in use, the cartridge sucks air into it from air hole. On top of the back chamber, there is a refill hole. For axial cartridges, HP injects ink into this hole and seal it with a plastic ball. The refill hole is not used by regular or startup cartridges, although they still have this opening and they still have the plastic ball. We cut open an axial cartridge. We can see the opening at the bottom of the dividing wall. But the same opening is placed on top of a regular cartridge. Therefore, we will only refill the front chamber for regular and startup cartridges.