A stretch blow molder turns preforms into bottles under heat and pressure, around the clock. That combination — hot, dry and fast — is hard on a small set of seals. When a SIDEL blow molder starts leaking air or losing pressure, the cause is usually one of a few positions, and the signs show up early if you know where to look.
The stretch rod seal
The stretch rod cycles every bottle, and its seal sees the most motion. The early sign is air loss at the rod or a slow pressure build that extends cycle time. A weeping stretch-rod seal does not recover — the material has already taken a set.
What to check: the stretch-rod seal and the rod surface it runs on; a scored rod chews through a new seal quickly, so replace in pairs.
The pneumatic cylinder seals
The mould clamp and blow cylinder are pneumatic, and their seals fail from the same heat and motion. Watch for the regulator needing to be turned up to do the same work, or a cylinder that drifts out of position. Both point at a seal that is no longer holding.
What to check: the cylinder rod seals and piston seals first, then the rod or bore they run against.
High-temperature O-rings and why material matters
Several positions run warm, and a standard O-ring there hardens and cracks early. The material is the difference between a seal that lasts and one that fails in weeks. We can supply the producing factory’s material certificate with the shipment on request, so you can confirm the grade is right for the temperature — we do not state compliance on the website, because the responsibility for the part sits with the maker, not the listing.
Contamination and scoring
PET dust and stray preform fragments are abrasive. A seal running against a scored surface fails fast, and debris in the bore accelerates the next failure. Clean the bore when you change a seal; fitting a new seal into a dirty one just restarts the clock.
What to check: the bore and mating surface at every seal change, plus the air filtration upstream of the pneumatic cylinders.
Two rules that hold
Replace in pairs where a worn part has been running against another, and confirm the part by the number in your machine’s spare-part book — a blow molder built over several years often carries superseded numbers for the same seal.
If the number on the part differs from the one in the book, send us both — we reply with a quotation within one business day, and can supply the material certificate on request.
All brand names, trademarks, and model numbers mentioned on this website are the property of their respective owners. Their use is for identification and reference purposes only. JP Machinery supplies compatible spare parts and is not an authorized distributor or representative of KRONES, SIDEL, KHS, SACMI, or AROL.