GACP External Tube Packer is standard packer which regards longer sealers, cement slurry or other liquids as expansion media. Double four-chamber valve system doubles flow area and reduces erosion to seats, cylinders and expansion channels. The stiffener can improve the strength of the tail sleeve. The stiffeners are in contact with the wellbore to provide flexible expansion space for the unreinforced central section, and to seal irregular open holes more effectively.