PET bottle blowing stretches and inflates a heated preform inside a mould using high-pressure air. The process typically requires 30–40 bar, far above general plant air, so it uses a dedicated booster or high-pressure compressor rather than the standard 7–8 bar network.
Sizing the high-pressure supply
Calculate the air volume per bottle, the number of cavities and the blowing rate per hour. Add the low-pressure air used for preform handling and stretching, plus a buffer for peaks. The high-pressure stage is usually fed by a low-pressure screw compressor that delivers air to a booster, with storage receivers at both pressure levels.
Why air quality matters
Moisture and oil in the blowing air leave streaks, haze and defects on the bottle wall, and can contaminate beverage containers. High-pressure air must be dried to a low dew point and filtered, with point-of-use treatment at the blowing station.
Design tips
Use generous receiver capacity to smooth the rapid, cyclic demand of blowing. Size the booster for the simultaneous demand of all cavities and confirm the duty cycle so the machine does not overheat during sustained production runs.