Combination control valve, particularly suitable for thermoelectric power plant

A combination control valve particularly suitable for thermoelectric power plant, what comprises:

• a valve body provided with a fluid inlet and outlet,
• a first seat on said outlet for a main valving member provided with balancing holes and slidable along a guide by way of interposed seal elements balancing the valving member, and
• a pilot valving member rigid with a valve stem to cooperate with a second seat present within said main valving member and provided with a spring-loaded shoulder cooperating with the main valving member, a trim member located in the valve body and reducing the fluid pressure and
• a seal system located between said first seat and said valve body wherein said seal system comprises a double gland which straddles a lantern sleeve with an intermediate vent for detecting leakages, is installed between said valve stem and the main valving member guide, and is pressed axially by preloaded elastic elements,
• said guide being held and elastically pressed by a plurality of preloaded elastic elements against a surface of a shoulder ring and said shoulder ring being retained in position by circular sectors fitted into the valve body, said surface of said shoulder ring being of an inclination different from that of said guide,
• said seal elements balancing the main valving member and being interposed between said guide and said main valving member wherein said seal elements comprise a series of labyrinths and said pilot valving member has a parabolic profile,
• said trim member reducing the fluid pressure comprising at least one hollow cylindrical structure inserted coaxially into a corresponding end cavity in said main valving member, said hollow cylindrical structure having a series of transverse holes arranged offset from a corresponding series of transverse holes provided in the walls of said cavity of said main valving member, and terminating with a parabolic profile, and wherein the seal system between said first seat and said valve body comprises an elastic seal element fixed between said first seat and said valve body.