A technique is provided to facilitate pumping of fluids in a well. A submersible pumping system utilizes a submersible motor to power a submersible pump. A motor protector works in cooperation with the submersible motor to protect motor fluid within the submersible motor and to reduce differential pressures between the internal motor fluid and the external well fluid. The motor protector incorporates a piston slidably sealed within an interior cavity of the motor protector for movement to reduce undue differential pressures.