Differences Between Glass and PET Bottles in Filling Lines

Views: 2441 Author: Howie SUN Publish Time:
A filling machine is specified from the product and the package, and every other number follows: viscosity and carbonation pick the valve, the neck finish picks the capper.
Key facts at a glance
What is includedFilling, capping and closing equipment
Filling principlesGravity, volumetric, isobaric, piston, load cell
Output range2,000-48,000 BPH by configuration
Accuracy basisVolume, weight or fill level
Wetted partsSUS 304 product contact, CIP-ready
Key controlFill accuracy, closure integrity, CIP time

Which filling principle fits this product?

The product fixes the filling principle; output only fixes the size. Still liquid at a steady density runs gravity or volumetric; carbonated product needs isobaric; thick product with solids needs a piston; product sold by weight runs a load cell. Fix the product first; a machine chosen before it is a machine chosen twice.

What actually decides fill accuracy?

Four variables sit behind a fill number: the dosing principle, the product temperature, the bottle geometry, and the condition of the valve or piston seal. A machine that holds its tolerance on the factory test can drift in the plant when the product arrives warmer or the bottle wall gets thinner.

PrincipleDoses byFails when
GravityFill level in the bottleBottle geometry varies
VolumetricChamber volumeValve seal wears
IsobaricVolume under counter-pressurePressure or temperature drifts
PistonDisplacementProduct carries solids
Load cellNet weightProduct temperature moves

The specification sheet for the Gravity Filling Machine for Still Water carries the utility figures quoted here.

What should the acceptance test measure?

Rated output at the specified format, fill accuracy on a defined sample, closure torque or seal measurement, and a timed changeover with the buyer watching. Anything not measured before sign-off becomes a discussion after the final payment.

The Volumetric Filling Machine for Still Water is the matching unit when this becomes a line project.

What is the real changeover cost?

The parts cost is small; the time is not. A format change touches star wheels, guide rails, grippers, the cap chute and the recipe. On a line with two formats and two changes a day, the annual hours lost exceed the price of a second small machine in many plants.

The same question is worked through from another angle in Comparing Linear vs Rotary Filling Machines: Pros, Cons, and.

How does the bottle neck finish change the machine?

The neck finish sets the rinser clamp, the filling valve seal and the capping head. A change of a millimetre in the thread is a change of change parts and often of the capper. It is the single most under-specified item in a filling line enquiry.

How to read the numbers. Rated capacity in this note follows the product specification range, not a factory acceptance test. Changeover, CIP and downstream stops sit outside a rated BPH, so plan on 0.65-0.85.

Frequently asked questions

What is the difference between volumetric and gravity filling?

Gravity fills to a level set by a tube, so accuracy depends on the bottle. A volumetric filler measures a chamber volume, which keeps it accurate when the format changes. Gravity is simpler and cheaper; volumetric is more repeatable when the bottle changes.

How accurate is a filling machine?

It depends on the principle and the product. A volumetric or load cell filler holds a tighter band than gravity on a variable bottle. The tolerance belongs in the acceptance protocol, measured by weight on a defined sample.

Can one filler run different bottle sizes?

Yes, with change parts: star wheels, guide rails, grippers and a recipe. The parts are cheap compared with the changeover time, which is why most plants specify one dominant format.

Why does the fill level vary between bottles?

Bottle capacity variation, product temperature, valve wear or foam. On glass, mould-to-mould capacity variation alone is enough to make level filling inconsistent, which is why glass lines often check-weigh.

What spare parts should be kept in stock?

Valve seals, piston seals, capping head inserts, guide rail blocks and one set of change parts for the second format. These are the items that stop a line for days when they fail.

Key takeaways
  1. The product picks the filling principle; the output only picks the size.
  2. Fill accuracy is a temperature and wear question as much as a machine question.
  3. Count CIP as lost production time, not as housekeeping.
  4. Line enquiries rarely specify the neck finish, and it is the item that decides the most change parts.
About the author
Written by the Sunswell engineering team - led by Howie SUN, Founder & CEO, with 14 years in filling and blow-moulding equipment R&D and turnkey project delivery across 71+ countries.
Last reviewed: 2026-08-28 . Reviewed by Sunswell engineering team
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