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 gate. The chamber is comprised of a plurality of longitudinally extending, side-by-side belts supported on a plurality of transverse rollers. The chamber is adjusted by a pair of belt tension rollers engaged with the bale chamber belts and supported between a pair of pivotally mounted belt tension arms which are displaceable as the diameter of a bale in the chamber increases during formation. A hydraulic circuit controls the tension applied to the chamber by the belt tension arms and rollers and also operates the bale discharge gate. A pair of hydraulic jacks are, respectively, mounted on each side of the baler and connected between the bale discharge gate and the belt tension arms. To properly tension the belts, a nonreturn valve isolates the hydraulic jacks from the tractor's hydraulic supply and the jack chambers are connected in closed circuit through an adjustable pressure valve to apply a resistance to fluid flow from one chamber of each jack to the other. The nonreturn valve is pilot controlled and is opened to permit return fluid flow to the tractor supply when the jacks are actuated to open the rear gate. Thus, each jack performs a double function of braking the movement of belt tension arms and rollers and operating the bale discharge gate, thereby, providing a simple, low cost, hydraulic circuit for belt tensioning and gate operation.