Liquids are the most challenging application for sachets
Powder falls, granules trickle—but liquids and pastes don’t do any of this on their own. They must be conveyed, precisely portioned, and placed into the pouch without spilling a drop, and they leave behind in the seal what doesn’t belong there. The sachet filling line for liquids and pastes is therefore more than just a sachet machine with a different dosing unit: product feeding, pump technology, and cleanability define the line. The machine base is the same as in the Packaging Machine described—this article focuses on aspects specific to liquids and pastes.
Overview of System Components
A liquid sachet production line consists of five sections:
- Product Feeding: Storage tanks with a capacity of 30 to 200 liters; equipped with an agitator for products that settle; double-walled and heated for pastes that need to be kept warm (chocolate, caramel).
- Conveyor unit: Product pump or pressure tank that conveys the product from the container to the dosing point—parts in contact with the product are made of stainless steel: SS316 for aggressive media and SS304 for standard food products.
- Dosing station: The metering pump is located directly above the filling tube and dispenses the batch in a metered quantity into the open plastic tube.
- Sealing and Separation Station: Longitudinal and transverse seams, as with any sachet machine—with the difference that product residue in the seam is the main source of defects here (see the article on Sealing Technology for Sachets).
- Derivation and Verification: Conveyor belt for collection or direct transfer to the reweighing station and case packer.
A Comparison of Pump Types
| Pump Type | Capacity | Accuracy | Strengths | Borders |
|---|---|---|---|---|
| Piston Dispenser | 0.5 to 50 ml | ±0.5 % | Paste-like and high-viscosity products, high precision | Product contact, cleaning effort |
| Peristaltic pump | 1 to 30 ml | ±0.5 to ±1 % | Conveyance via the hose only—fastest product changeover, hygienic | Hose is a wear part; do not use coarse pastes |
| Time-Pressure System | 5 to 50 ml | ±1 to ±2 % | simple, affordable | Temperature-dependent viscosity affects accuracy |
| Diaphragm Dispenser | 2 to 40 ml | ±1 % | aggressive media, sealed | limited viscosity range |
The rule of thumb: low-viscosity surfactants and juices are dispensed using time-pressure or peristaltic pumps; creams and gels using a piston dispenser; and aggressive or sterile products using a diaphragm or peristaltic pump. The choice of method depends on the product specifications—viscosity in millipascal-seconds, shear behavior, and temperature range.
The Drip Problem: Three Technical Solutions
Every drop on the outside of the bag poses a hygiene and sealing problem. Three established designs keep the filling tube dry:
- Suction stroke: After dosing, the piston pump briefly draws back the contents of the fill tube—the standard procedure for piston dispensers.
- Nozzle end: A needle valve or ball valve at the end of the fill pipe that mechanically shuts off the product flow; required for low-viscosity products.
- Pipe Flushing with a Gas Shield: An annular gap around the filling tube blows air or nitrogen against any droplets that form—at the same time, the gas inertizes oxygen-sensitive products inside the sachet.
Cleaning: Design for CIP
Liquid and paste production lines are cleaned more frequently than powder systems—ranging from daily to with each product change. A CIP-compatible design means: cleanable product pathways without dead spaces, quick-release hose connections, and a dosing pump that can be rinsed while installed. The selection criteria are detailed in the article on Cleaning and Hygiene. Companies that run multiple products on a single line should schedule cleaning time as part of production time: typically 30 to 60 minutes per changeover, including drying.
Performance and Format
Liquid sachets run in a single lane at a rate of 30 to 80 sachets per minute—multi-lane liquid systems are more complex than powder stick packs because each lane requires its own dosing section. Formats are 4-side seals with widths of 40 to 100 mm and lengths of 50 to 150 mm; typical fill volumes range from 2 to 30 ml (cosmetic samples) or 5 to 50 ml (sauces, oils, syrups). The comprehensive overview of all liquid packaging topics begins with the Packaging Solution for Liquids.
Frequently Asked Questions
What level of dosing accuracy do liquid sachet filling systems achieve?
Piston and peristaltic metering achieve ±0.5 % of the setpoint for fill volumes starting at 0.5 ml; Time-pressure systems have a tolerance of ±1 to ±2 %. A stable product temperature is crucial because viscosity affects the flow rate.
Can creams and gels be packaged in sachets?
Yes, with a piston dispenser and heated product path—high-viscosity pastes with a viscosity of more than 10,000 millipascal-seconds require heat and smooth, wide product paths without changes in cross-sectional area.
What happens if there are product residues in the seal?
The seam strength decreases, and the bag starts to leak—ultrasonic sealing is the most tolerant of residue; otherwise, vacuum extraction, pipe flushing, and precise dosing timing prevent contamination. See the article for details Sealing Technology for Sachets.
Is a multi-lane system for liquids worth it?
For stable production volumes, yes—two to four lanes can double or even quadruple output. Prerequisite: Each lane requires its own dosing section, which increases both the investment and the cleaning requirements.
Related pages: Packaging Solution for Liquids | Vertical Filling and Sealing Machine | Cleaning and Hygiene in Packaging | VFFS Guide
Request technical specifications and a quote for your production line. Please specify the product, bag size, and target output (bags/min.) – Request Technical Specifications and a Quote.
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