System for adjusting the pressure of a gas

A system for adjusting a pressure of a gas, comprising:

• a flow duct for said gas;
• first shutter means arranged in said flow duct for causing a pressure drop from a supply pressure present in a first area of said flow duct, upstream of said first shutter means with respect to a flow direction of said gas, to a delivery pressure present in a second area of said flow duct, downstream of said first shutter means;
• pilot means for providing a pilot pressure depending on a difference between said delivery pressure and a predefined setting pressure;
• first drive means operated by said pilot pressure for varying a degree of opening of said first shutter means in such a way that, when said delivery pressure exceeds said predetermined setting pressure, the degree of opening of said first shutter means is reduced, and vice versa;
• second shutter means arranged in said flow duct in series to said first shutter means, said second shutter means assuming a closed configuration in which said second shutter means tightly close said flow duct;
• second drive means operated by said pilot pressure for varying a degree of opening of said second shutter means in such a way that, when said delivery pressure exceeds said predetermined setting pressure, the degree of opening of said second shutter means is reduced, and vice versa;
• said first drive means and said second drive means being configured so as to control said first shutter means and said second shutter means in such a way that, when said first shutter means are open, said second shutter means produce in said gas a second pressure drop that is smaller than a first pressure drop produced by said first shutter means;
• wherein said first drive means and said second drive means are configured in such a way as to control said first shutter means and said second shutter means so that when said first shutter means are open, said second shutter means define a second flow area that exceeds a first flow area defined by said first shutter means.