a cylindrical baler is comprised of an adjustable bale forming chamber for forming spirally wound , cylindrical bales . a completed bale is discharged on the ground through a rear tailgate . the chamber is defined by a plurality of belts supported on a system of rollers . tensioning cylinders are mounted on each side of the baler to provide variable bale density and tailgate cylinders are positioned on the rear of the baler to actuate the tailgate after a bale is formed . a two - way proportional valve acts alone or in cooperation with an adjustable rotary valve and an adjustable relief valve to coordinate the flow , to vary the belt tension , and to open and close the tailgate .