The Dual Circulating Sub provides a mens of emergency circulation through a ball-operated circulating feature. The ball-operated valve shifts open when a ball is dropped to the tool and pressure is applied to exceed the predetermined shear value of the valve.
Once shifted, circulation is diverted to the annular area. However, the Dual Circulation Sub also offers an over-pressure differential activated piston. The piston activation pressure can be predetermined at surface through shear pins.
