Each turbine on the Disa is equipped with its own shell valve system allowing for a precise flow of abrasive to each turbine. The position of the valve assists in reducing the wear of the machine housing. The Barrier Switch measures the material length and stops the abrasive flow when then trailing end of the machine has passed thus reducing wear within the machine. These valves are adjustable allowing the correct amount of abrasive to flow to the turbine achieving optimum performance.