an ink cartridge has a housing with an ink reservoir . the housing has a first vent , a second vent , and an opening . the ink reservoir has an air bag to adjust pressure within the ink reservoir . the ink cartridge further has an elastic restricting device that prevents ink in the ink reservoir from seeping through the opening . an elastic plug plugs the second vent of the housing , and an active shaft is movably installed in the well for pushing the elastic plug . when consumption of ink causes the air bag to expand to a predetermined degree , the air bag moves the active shaft , the active shaft pushes the elastic plug , and air enters into the ink reservoir through the second vent to reduce the volume of the air bag . when the air bag stops moving the active shaft , the elastic plug plugs the second vent .