These cartridges are able to retain the ink inside due to a slight vacuum. The ink starts leaking the moment the vacuum is lost.
The vacuum retained inkjet cartridges are complex in design and less common, mostly made by Hewlett-Packard. It can require a small modification when refilling such as using; hot glue, screw, or other types of tight seals.
Before you start refilling these Ink Cartridges, make sure to squeeze them to create appropriate vacuum. Do not panic on seeing few drops of ink getting leaked out, this means that vacuum has stabilized. But if those drops progress into continuous dribbles then this indicates that the seal is not tight enough.
The refilling process is accompanied by applying an air-tight seal on the cartridge.The cartridge can be sealed by hot wax, silicone rubber or hot glue.For effective and quick sealing hot glue is recommended.
Some of these cartridges come with a filter screen placed above the print head.The original ink tends to form foams when in contact with air. So, your first refill is most likely going to give you streaky and untidy print outs. The foam obstructs the ink flow, but this can be overcome if you rinse the cartridge before the first refill. The problem is gradually solved after subsequent refills.
The vacuum retained cartridge is much more difficult to refill than sponge filled cartridges.