Patent ID: 7530781

Claim:
A pump device for pressurizing a fluid to be fed, comprising: a rotary shaft, a bearing including a bearing surface adapted to face to the rotary shaft so that the rotary shaft is supported on the bearing surface in a rotatable manner, an impeller fixed to the rotary shaft to be rotatable with the rotary shaft so that the fluid is pressurized by a rotation of the impeller, a balance disk fixed to the rotary shaft in an axial direction of the rotary shaft and including first and second surfaces opposed to each other in the axial direction and configured to receive first and second pressures, respectively, so that a difference between the first and second pressures generates a force in the axial direction to be applied through the balance disk to the rotary shaft, a motor including a rotor connected to the rotary shaft to rotationally drive the rotary shaft, and a motor chamber in which the rotor is rotatable, wherein the pressure of the fluid in the motor chamber is less than one of the first and second pressures less than the other one of the first and second pressures, and is more than a pressure of the fluid before being started to be pressurized by the impeller.