This paper addresses the control of a pressure regulator which reduces the pressure from an upstream chamber to a desired lower pressure in a downstream one. Most results in the literature, either neglect the actuator dynamic embedded in the reducer, or develop a specific design dedicated to their system. In this study, we propose to take into account this inner dynamic with a control system designed independently. The objective is to enable a modular architecture. It also justifies classical cascade control approach. A modeling work of the physical system combined with some practical assumptions provides a simple linear model. An output feedback control is designed to ensure stability, performance requirements and to cope with a saturation nonlinearity. This phenomenon is necessarily present due to physical limitations of the fluid flow rate in the actuator. Robust analysis approach and sector condition are used to address this feature as well as to take into account the dynamic of the independent controlled actuator with reduced assumptions on this subsystem. Stability condition of the overall system is expressed with LMI tests. Simulation and experimental tests show the validity of the proposed methodology.