Abstract: An adjustable bladder assembly for use with a closed hydraulic power system is provided. The bladder assembly includes a rigid body and a bladder cover slidably engaged therein. The bladder cover divides an interior area of the bladder assembly into first and second portions. The first portion of the bladder assembly is configured to be in fluid communication with a fluid reservoir of the hydraulic power system, with internal pressure of the hydraulic power system acting on an inner surface of the bladder cover, thereby biasing the bladder assembly towards an inflated configuration. The second portion of the bladder assembly is open to the environment such that ambient air pressure acting on an outer surface of the bladder cover biases the bladder assembly towards a deflated configuration.