Exploring Isobaric Filling: Core Technology for Carbonated Drinks (Mid-Autumn Special)

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Isobaric filling is the only way to put a carbonated drink into a bottle without losing the gas, which is why a still water filler cannot be converted by adding a CO2 unit. During filling, the machine equalises the pressure inside the liquid tank and the empty bottle.

Exploring Isobaric Filling: Core Technology for Carbonated Drinks (Mid

Key facts at a glance
Valve typeIsobaric, CO2 counter-pressure
Output range12,000-36,000 BPH at 0.2-2 L
ContainersPET bottle, glass bottle, aluminum can
CO2 handlingPre-pressurisation and return pipe, no venting
ValvesMechanical, semi-electric or volumetric
Line scopeWater treatment, syrup mixing, carbonation, filler, pack

Why does carbonated product need isobaric filling?

A carbonated drink is a saturated solution held in equilibrium by pressure and temperature. If the filler exposes it to atmosphere, CO2 leaves the liquid as foam and the fill level collapses. Isobaric filling pressurises the bottle to the bowl pressure first, fills under counter-pressure, then releases in a controlled ramp.

Filling temperature and pressure are two critical parameters that directly control gas content, flavour consistency and shelf stability.

How do you size a CSD line without oversizing the CO2 plant?

Size the filler on peak shift demand with a production factor of 0.65-0.85, then size the CO2 supply on average consumption, not peak. A CO2 plant built for the filler nameplate runs partly loaded for most of the year and loses more gas to vaporisation than the line saves in speed.

As beverage manufacturers ramp up production ahead of seasonal peaks like Mid‑Autumn, precise temperature control becomes even more vital.

Valve typeSettingBest for
MechanicalFixed cam profileSingle product, long runs
Semi-electricSignal-timed open and closeRecipe changes within one product family
VolumetricChamber dosePressure or temperature drift during the shift
Isobaric + volumetricChamber dose under counter-pressureHigh CO2 with tight fill accuracy

The Isobaric Filling Machine for CSD and Sparkling Water is the reference unit for this configuration.

How is syrup mixed and carbonated before the filler?

Syrup is proportioned and blended with treated water, then carbonated under pressure and temperature control. The ratio accuracy and the carbonation stability decide the product, and both are upstream of the filler. A filler cannot correct a drifting blend.

③ Intelligent PLC control system: A programmable logic controller manages the entire workflow, with tidy wiring, simple operation and convenient routine maintenance.

Rated output, change parts and services are listed on the CSD & Sparkling Water by Mechanical Filler page.

What does warm product do to a CSD line?

Warm product holds less CO2 at the same pressure, so the filler either loses gas or needs a higher pressure that increases foaming. Chilling before carbonation is the standard answer, and the chiller capacity belongs in the utility schedule.

The same question is worked through from another angle in How Nitrogen Dosers Enhance CO2 Retention, Taste Preservation, and.

What is overfoaming at the filler and how is it controlled?

Overfoaming is gas leaving the product too fast at the end of fill. The pressure release has to be ramped, not dumped, and the fill height has to leave the right headspace. A snift valve that opens too early turns a good fill into a wet bottle.

This balanced pressure environment prevents CO₂ from escaping and stops foaming or overflow.

How to read the numbers. Every figure in this note is a reference range from the product specification, not a guaranteed output. A rated BPH is measured at one CO2 level and one temperature; format changes and CIP sit outside it, so size on 0.65-0.85.

Frequently asked questions

Can one filling machine run both still water and CSD?

No. Carbonation needs isobaric valves under counter-pressure; still water runs gravity or volumetric. A combiblock can carry both valve sets, but they are specified separately and are not interchangeable at the push of a button.

What CO2 level can an isobaric filler hold?

It holds what the mixer sets and the temperature allows. Most CSD runs between 2.5 and 4.0 volumes, with the target set per product. Retention, not the mixer set point, is what the acceptance test should measure in the filled bottle.

How many cans per hour is 24,000 CPH?

400 cans per minute. CPH and BPH are different units and cannot be compared directly, because can and bottle formats carry different volumes and different downstream equipment.

What is the difference between 2.5 and 4.0 volumes of CO2?

The higher the volumes, the sharper the mouthfeel and the more pressure the package must hold. Higher carbonation also needs a colder fill and a tighter pressure ramp, so it reduces practical line speed.

Can a CSD line fill glass bottles?

Yes, with a different infeed, spacing and capping set. Glass needs mechanical spacing rather than an air conveyor, and the filler runs at 4,000-20,000 BPH on glass against 12,000-36,000 BPH on PET.

Key takeaways
  1. Carbonation is a pressure and temperature problem before it is a valve problem.
  2. Size the CO2 plant on average demand, not on the filler nameplate.
  3. Warm product loses CO2 before the filler can dose it.
  4. A can line and a PET line share the valve principle, not the closing equipment.
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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