Patent ID: 8807966

Claim:
An electric submersible pump device, comprising: an electric submersible motor part that produces torque having coupled thereto a drive shaft that transmits the torque, the drive shaft extending in an axial direction from the motor part; a protector part coupled with the motor part, the drive shaft extending into the protector part, the protector part comprising a tubular shaped casing extending in the axial direction; a shaft tube surrounding a portion of the drive shaft thereby defining an interior space between an outer surface of the shaft and an interior of the shaft tube, the interior space isolated from the motor part by at least one seal, and defining a circumferential exterior space between an exterior of the shaft tube and a circumferential interior of the tubular shaped casing; a first shaft seal at a first end of the shaft tube; a second shaft seal at a second end of the shaft tube; a passage in fluid communication with the interior space via an opening in the shaft tube; and a compensating element disposed at least partially in the exterior space and in fluid communication with the passage, the compensating element being an expandable and contractible vessel defining a volume that is correspondingly expandable and contractible to pressure-balance the interior space to prevent excessive positive and negative pressures on the first and second shaft seals.