Hydraulic couplings will transmit torque equal to the input torque by means of energy changes in a rotating vortex of liquid. For the vortices to form there must be __________.

Correct Answer: Option A — slip between the impeller and runner

Hydraulic couplings operate via kinetic energy transfer from the impeller to the runner. Because torque transmission relies entirely on fluid momentum exchange, a speed differential, or slip, must continuously exist between the driving impeller and driven runner to maintain the rotating fluid vortex.