Subsea actuator assemblies and methods for extending the water depth capabilities of subsea actuator assemblies

Abstract

A hydraulic pressure compensation system for valve actuator assemblies is described having particular application for subsea wellhead installations. The compensation system includes at least one valve actuator assembly having a housing that retains a reciprocable piston therewithin. The piston is spring biased into its fail safe configuration. The valve actuator assembly is hydraulically associated with an accumulator reservoir that defines a closed fluid reservoir and an open fluid reservoir that is exposed to ambient pressures. The two chambers are separated by a membrane. The valve actuator assembly is also operationally associated with a fluid pressure intensifier that boosts the ambient pressure of the accumulator so that an increased fluid pressure may be transmitted to the actuator assembly to bias the actuated valve toward its fail safe configuration. In a described embodiment, the fluid pressure intensifier comprises a housing that defines a chamber having a fluid inlet and fluid outlet. A dual-headed piston is moveably retained within the housing. The piston has an enlarged piston face and a reduced size piston face. Fluid pressure entering the fluid inlet is exerted upon the enlarged piston face, and due to the difference of piston face sizes, an increased pressure is transmitted out of the fluid outlet.