A rotor seizure can be due to a loss of clearance between the hydraulic head and rotor during the transient (or
warm-up) condition. Heat generated by shearing the oil film at the hydraulic head to rotor interface causes heating
of the hydraulic head and rotor. Because the mass of the rotor is less than that of the hydraulic head, it heats and
expands at a faster rate. The clearance at the interface of the hydraulic head and rotor is thereby reduced and the
possibility of rotor seizure is introduced.
The rotor seizures in a test series occurred at the midpoint of the rotor length indicating that the maximum rotor
heating and expansion occurred at the midpoint. Therefore, a relief groove was added to the diameter of the rotor,
as shown in Figure 4-77 to minimize the potential for rotor seizure following a cold, high speed acceleration.
