Pump apparatus

A pump apparatus comprising:

• a housing including a suction port and a discharge port;
• a shaft rotatably supported in the housing;
• a rotator disposed in the housing, the rotator being configured to rotate in accordance with rotation of the shaft so as to transfer hydraulic oil to the discharge port, the hydraulic oil being sucked from the suction port;
• a pressure relief passage defined in a portion of the housing facing an outer peripheral surface of the shaft, the pressure relief passage being configured to bring the discharge port into communication with a low pressure region where the hydraulic oil is low in pressure;
• and
• a bearing disposed on the pressure relief passage, the bearing supporting the shaft such that the shaft is rotatable relative to the housing, wherein
• when a pressure of the hydraulic oil in the discharge port is lower than a first predetermined pressure, the bearing keeps the pressure relief passage out of communication with an adjacent hydraulic oil passage, and
• when the pressure of the hydraulic oil in the discharge port has increased to reach or exceed the first predetermined pressure, the bearing axially moves relative to the housing so as to bring the pressure relief passage into communication with the adjacent hydraulic oil passage.