Method and apparatus for stretching and blowing up a heated preform

Method of stretching and blowing up a preheated preform comprising the steps of:

• providing a single pressurized air supply which feeds pressurized air to a pneumatic piston, to the inside of the preform, and against a sleeve;
• feeding pressurized air furnished by said pressurized air supply to the piston thereby displacing a stretching rod into the preform until the stretching rod has contacted a closed end of the preform;
• feeding pressurized air furnished by said pressurized air supply against the sleeve to move said sleeve relative to and in the same direction as said rod until an open end of said preform is sealed against said sleeve and said sleeve is forced into sealing contact with said open end of said preform with a sealing pressure that varies as the pressure of said pressurized air;
• and
• after the rod has contacted the closed end of the preform and the preform has been selected against said sleeve, further feeding pressurized air to the piston to mechanically stretch the preform longitudinally and simultaneously feeding pressurized air from said pressurized air supply to the inside of the preform to blow up the preform thereby transversely deforming the preform during the mechanical stretching using said single pressurized air supply.