Purging system for ink jet recording apparatus

In an ink jet recording apparatus comprising:

• an ink-on-demand type recording head which jets recording ink through nozzles thereof to make recordings, said recording ink being forcibly sent from a pressure chamber of said recording head to said nozzles;
• and
• an ink cartridge comprised of an ink container bag filled with said recording ink and an ink cartridge body which houses said ink container bag, said ink container bag having at least a flexible portion;
• the improvement comprising:
• said ink cartridge body being a closed-up, substantially rigid body having at least one opening therein for permitting gas to selectively flow in and out of said substantially rigid cartridge body, said cartridge body housing said ink container bag;
• a pressurizing gas supply means which selectively supplies gas under pressure to said at least one opening of said ink cartridge body for increasing the pressure inside said ink cartridge body when it is selectively supplying said pressure gas to said at least one opening of said ink cartridge body for thereby increasing the pressure around the outside of said ink container bag and thereby increasing the pressure of the ink inside said ink container bag due to flexing under said increased pressure of said flexible portion thereof;
• a cap made of an elastic material and coupled to said ink container bag in a liquid tight manner for supplying said recording ink from inside said ink container bag into said recording head under said pressure to purge said recording head of bubbles and of ink previously contained therein when said gas supply means is supplying said pressure gas to said at least one opening of said ink cartridge body;
• and
• means for selectively venting said at least one opening of said ink cartridge body to prevent said purging of said recording head.