HP (individual cartridge) printers...

HP printers with individual ink cartridges use ink level chips. HP "ink" chips also store expiration date for each cartridge, which
renders the cartridge useless at a preset date. There is a solution to the HP ink level chip issue. We have resetters for # 14 ink
cartridges, as well as "always full" ARC chips for # 02, 10, 11, 12, 82, 88 etc cartridges. Your best option is to get some "refill
friendly" cartridges (with always full chips).        

Older HP printers...

Older HP printers don't use ink level chips to prevent refilling (some do). Instead each cartridge has ID number and the printer
keeps several ID's in memory (usually 3). When a refilled cartridge is fitted, the printer "knows" about it. Some HP printers do
let you print with "empty" cartridges, others don't. It is easy to reset the printer memory, if you want, but you will need 3 black
cartridges (to reset the black) or 3 colour cartridges (to reset the colour). They can be full or empty, it doesn't matter as long
as the electronic circuits are ok. All you have to do is install the first one in the printer, let the printer recognise it...then install
the second...then the third. And by the time you get to the "refilled" cartridge, the printer will see it as a NEW full one. It's not
as complicated as it sounds...