Butterfly valve, preferably for a blow off circuit of a gas turbine plant

A butterfly valve (12), preferably for a blow off circuit (9) of a gas turbine plant (1), is provided with: a supporting ring (18), which is provided with an inner perimeter edge (25) defining a fluid flow section (27), and with an annular seat (29) arranged along the inner perimeter edge (25); a disc (23), which is pivoted to the supporting ring (18) and is mobile between a valve closing position (12), wherein the disc (23) obstructs the fluid flow section (27), and a valve opening position (12), wherein the disc (23) does not obstruct the fluid passage section (27) allowing the flowing of the fluid; a sealing ring (22) partially housed in the annular seat (29) and adapted to abut against a peripheral edge (44) of the disc (23) when the disc (23) is in the valve closing position (12); the sealing ring (22) comprising an inner annular portion (34), which is contained in the annular seat (29), and a projecting annular portion (35), which projects radially from the annular seat (29) and is hollow.