Filling valve having a three-position valve rod

Filling valve (5) comprising:

• a hollow housing (11) having a valve seat (25);
• a moving valve rod (14) slidingly mounted in the housing (11) and having a sealing surface (23), said moving valve rod (14) and said hollow housing (11) together defining a liquid chamber (18);
• a liquid inlet (26) for putting said liquid chamber (18) into communication with a liquid supply pipe (6);
• a first piston (29) rigidly attached to the valve rod (14), slidingly mounted in the housing (11) and defining with respect to the same a first stroke (S1) between an upper position where the first piston (29) puts said valve rod (14) in a first, full-open position, in which said sealing surface (23) is spaced from said valve seat (25), thereby forming a passage (27) for the liquid, and an lower position where the first piston (29) puts said valve rod (14) in a second, closed position, in which said sealing surface (23) is in sealing contact with said valve seat (25), thereby closing said passage (27),
• a second piston (36) slidingly mounted in the housing (11) and defining with respect of the same a second stroke (S2) shorter than said first stroke, between an upper position in which the second piston (36) permits the first piston (29) to reach its upper position, and a lower position in which the second piston (36) blocks the first piston (29) in an intermediate position where the first piston (29) puts said valve rod (14) in a third, predetermined, semi-open position in which said sealing surface (23) is spaced from the valve seat (25) but closer to the same than in the full-open position,
• characterized in that said first piston (29) has a top end surface (45) which, in the upper and intermediate positions, comes into abutment with a bottom end surface (46) of the second piston (36).