Vertrad (asker) Aug 3, 2014:

context suplimentar When the drill string reaches the maximum preset torque during drilling, the swivel will stop but will continue to hold the torque windup already in the drill string. When torque comes up, the engine could die because it is not making enough HP at low rpm. Then the torque windup in the string would cause the engine & pump to spin backwards which will cause problems.