The present invention relates to a blow-molding installation for manufacturing thermoplastic hollow bodies by blow-molding or stretch-blow-molding containers (37) in a molding cavity of a mold, this blow-molding installation comprising a double-acting nozzle actuator (1) with two stages in series, equipped with two pistons (5, 6), these being an upper piston and a lower piston respectively, the nozzle (15, 16) being fixed removably, and pneumatic control means being designed to make said pistons (5, 6) slide according to a first operating mode used when the nozzle (15) is of the type that makes sealed contact with the mouth of the neck of the container, and a second operating mode used when the nozzle (16) is of the bell type with sealed contact against the surface of the mold in which the container (37) is placed.