Case drain

Hydraulic motors and pumps run case drain hoses.  The reason for this is to drain excess internal oil leakage from the motor.  This is certainly critical in a piston motor and pump as the pistons have some internal leakage as they are actually just metal on metal.  If no case drain hose is installed then the result will be, at the least, a blown shaft seal, and at worst, a split or damaged housing.Running a case drain can also assist with cooling, and also lubrication of the motors in some instances.