Pouch · Sachet · Stick pack leak testing
Pouch leak tester for sachets, stick packs and stand-up pouches
A pouch leak tester shows whether a small flexible package lets gas or product through its seals or film. With sachets, stick packs and stand-up pouches the hard part is the package, not the chamber: these formats are filled almost to the top, and a vacuum test only works when gas inside the package touches the spot being tested. This page covers where small packs leak, how DVACI's CDV2 and CDV3 acrylic vacuum chambers handle low headspace (a dry test, or internal pressurization with the PI kit under ASTM F2096), liquid and semi-liquid contents, throughput, and what the result cannot tell you.
Where small pouches and sachets leak
Small flexible packs have few seals, and a leak almost always starts at one of them. Knowing where tells you how to orient the sample.
- Fin seal. The lengthwise seal of stick packs and flow packs. A wrinkle or a trace of product in the seal leaves a channel, and bubbles tend to appear along a line.
- Cross seals. Heat, dwell time and jaw pressure act on a narrow strip; product in the strip prevents a full weld.
- Corners and junctions. Where the fin seal meets a cross seal, the film layers change and the jaws press unevenly. Stand-up pouch bottom corners also carry load when handled.
- Zipper. The track is welded into the side seals; its ends, where thickness changes, are common weak points. Decide whether the zipper is inside the area under test.
- Spout and fitment. The weld joins two different materials. Check its full circumference, and test the cap separately.
- Pinholes in the film. Flex cracking, abrasion and laminate defects open small holes away from every seal.
Low headspace: how a pouch leak tester deals with it
Vacuum testing works because gas inside the package expands when the surrounding pressure drops. If a path exists, the gas leaves and, under water, forms bubbles. So there must be gas inside, and it must touch the area under test.
Sachets and stick packs often fail both conditions. They are sealed with as little air as the machine can manage, and the small pocket sits wherever the product lets it. If product covers a seal, the gas cannot reach it, and a channel plugged by product shows nothing. Turn the sample so the pocket sits against the seal under test, and test each seal in turn. When no usable pocket exists, a CDV chamber offers two routes.
| Dry test (observing inflation) | Internal pressurization (PI kit, ASTM F2096) | |
|---|---|---|
| Principle | Vacuum around the pack. A tight pack swells and stays swollen; a leaker swells less, deflates or releases product. | Air is injected through a septum patch and needle with the pack under water. Bubbles mark the leak. |
| Gas inside the pack | A little, enough to see the change | Not needed |
| Locates the leak | Often not | Yes |
| Pack afterwards | Dry; a pack that passed may stay saleable (QA decision) | Punctured; destructive |
| Typical module | Module S (or M) | PI module |
Both are gross-leak methods, and neither detects every leak. For the bubble method itself, see the ASTM D3078 leak tester and bubble leak tester pages.
Sachet leak test, method 1: dry test by observing inflation
The dry test needs no water and no accessory. It suits packs that must stay dry, liquid-filled packs and quick screening.
- Prepare. Lay a clean white paper towel on the chamber floor.
- Place. Put samples in a single layer, spaced, never stacked. Note each position (A1, A2, B1).
- Start. Close the lid and press START on Module S. The regulator draws vacuum to the locked setpoint and the timer begins.
- Observe. A tight pack swells as its gas pocket expands and stays that way. A leaking pack swells less, swells then deflates, or lets product out.
- Vent and inspect. Module S vents automatically. Check each pack and the towel, then record the result.
Add a known-good reference pack to each cycle so a leaker stands out beside it. Keep the setpoint within what intact packs tolerate: the built-in Venturi reaches about −750 mbar (−22 inHg) at sea level, up to −800 mbar, and a thin sachet may open a good seal before that. A seal opened by the test is a finding, not a leak. The dry test is less sensitive than immersion and must be validated for your format.
Stick pack leak test, method 2: internal pressurization with the PI kit
With no usable headspace, bring the air with you. The PI module has a compressed-air inlet rated for a maximum of 2 bar (29 psi), a manual regulator, a pressure sensor, START/STOP, a 4 mm hose, a needle and rubber septum patches, and it is supplied with a pressure reducer. The CDV chamber is the transparent water bath. Full details are on the internal pressurization kit page.
- Close the regulator. Turn it fully counter-clockwise before connecting air and before every test.
- Connect the air. Use the pressure reducer supplied with the PI module. The air reaching the module must never exceed 2 bar (29 psi).
- Fit the patch. Press a septum patch onto a flat area, away from the seals under test. On a narrow stick pack, make sure it does not cover a seal.
- Submerge. Hold the pack about 25 mm (1 in) under water, patch reachable, all seals visible.
- Insert the needle through the patch, without piercing the opposite film.
- Pressurize slowly. Press START and open the regulator slowly, watching the sensor and the pack, up to the value in your validated procedure. If a seal starts to open, close the regulator and record a seal failure.
- Hold and look. A steady stream from one point is a leak. Bubbles at the needle or patch are a test artifact.
- Finish. Close the regulator counter-clockwise, press STOP, withdraw the needle and record the leak point.
DVACI gives no universal test pressure: 2 bar (29 psi) is the module's limit, while the limit that matters is what your film and seals tolerate. The test is destructive.
Stand-up pouch leak testing by immersion when headspace allows
Stand-up pouches usually hold enough air for the bubble test of ASTM D3078, described on the ASTM D3078 leak tester page. In a CDV3 the pouch lies on its side under the hold-down grid, about 25 mm (1 in) below the surface, with every seal visible. It swells under vacuum, so leave room. Bubbles from gusset folds or air at the zipper are not the continuous stream of a leak; a reference pouch helps operators tell them apart. Immersion wets the pack, so treat tested packs as scrap unless QA releases them.
Liquid and semi-liquid contents
Immersion rarely suits liquid, gel or paste: little gas forms bubbles, and outside water can mask a weep. Use the dry test, with these changes.
- Absorbent paper. Lay each pack on a fresh white paper towel, seal under test facing down. A wet spot or stain on the towel or chamber floor shows the leak and its position. Powder may leave dust instead.
- Why vacuum finds it. With outside pressure lowered, contents push outward and can cross a channel they would not cross at rest.
- A longer hold. Gas leaves a channel in seconds; viscous product crosses a narrow one slowly. Set the hold time with known defects rather than borrowing the gas-filled value.
- Dye as evidence. A clear liquid leaves a faint trace. In validation, fill test packs with a dyed simulant. Never do this with production product.
A thick product can plug a channel, so a clean towel means no leak was seen under these conditions. Clean spills from the acrylic with a microfiber cloth and no solvents.
Choosing a pouch leak tester: CDV2 or CDV3, Module S or PI
| Need | Configuration | Internal size (L × W × H) |
|---|---|---|
| Sachets and stick packs | CDV2 with Module S | 280 × 200 × 200 mm (11 × 8 × 8 in), 19 kg (42 lb) |
| Stand-up pouches, flow packs, several sachets per cycle | CDV3 with Module S | 450 × 300 × 250 mm (18 × 12 × 10 in), 38 kg (84 lb) |
| Little or no headspace | Either chamber plus PI module | As above |
| Test records per cycle | Either chamber with Module P | As above |
Module S gives START/STOP, a lockable setpoint, a timer and automatic venting, with units in inHg, mmHg, mbar, psi, kPa or MPa. It does not record results, so keep a log; Module P stores recipes and test records, with an optional printer and barcode reader. The built-in Venturi runs on compressed air (185 L/min at 5 bar, 6.5 CFM at 72 psi; maximum inlet 6 bar / 87 psi) and reaches about −750 mbar, up to −800 mbar. An optional electric pump goes deeper, to −900 mbar (oil-free) or −950 mbar (two-stage) at sea level. See also the CDV benchtop chambers.
Throughput: several units per cycle
- Use the grid. In immersion a hold-down grid keeps packs below the surface; in dry tests a flat tray or towel keeps them apart.
- Count the real floor. A CDV3 floor (450 × 300 mm) is about 2.4 times a CDV2 floor (280 × 200 mm), but a water tray, the grid and inflation reduce it.
- One layer, labeled positions. One format and orientation per cycle, every seal visible. Retest a misbehaving pack alone.
- Let the module run the cycle. Load, close, START, hold, automatic vent, inspect.
- Match method to volume. Screen many units with the dry test; use internal pressurization to confirm a suspect pack or test lots with no headspace.
Set vacuum and hold with known-good and known-leaking samples
- Prepare intact packs and packs with known defects. DVACI supplies 50 µm tungsten wire and calibrated pins of 150 and 250 µm for control defects.
- Raise the vacuum on intact packs until a seal yields; your working range lies below it.
- Test defective packs at several vacuum levels and hold times and count detections.
- Choose the lowest combination that detects the smallest defect that matters, and confirm it on a larger run.
- Lock the setpoint (Module S) or store a recipe (Module P) and write the parameters into the SOP.
The user defines and validates the vacuum level and hold time.
What a pouch leak test cannot prove
- It is probabilistic. Under USP <1207.2>, bubble emission and dye tests detect a given leak with a probability below 1. This is not statistical sampling. It depends on defect size, contents, orientation, parameters and observer. See probabilistic and deterministic methods.
- No bubbles is not no leak. It means none was seen under those conditions. Small channels and fine pinholes can be missed or plugged by product.
- It targets gross leaks. Where your risk assessment needs smaller defects, a deterministic method such as vacuum decay (ASTM F2338, a different technology) works alongside it.
- It says nothing about seal strength or barrier properties. An airtight seal can be weak. Seal strength needs a separate test.
- It consumes samples. Immersion wets, internal pressurization punctures.
The test plays a defined, documented role inside a complete package integrity program. All our methods are on the test methods page, and the full range on vacuum leak testers for packaging.
Frequently asked questions
Can a vacuum test find a leak in a sachet with almost no air inside? Not reliably by bubble emission. Bubbles need gas that can escape through the defect and that touches it. With little or no headspace, use a dry test, which watches for loss of inflation or product release, or internal pressurization with the PI kit, which supplies the air from outside. Both are gross-leak methods, and neither detects every leak.
When should I use the PI kit instead of the dry test? Use the PI kit when the pack has no usable gas pocket, when you must see where it leaks, or when you want to confirm a suspect pack from a dry test. It follows ASTM F2096 and destroys the sample. The inlet maximum is 2 bar (29 psi), the module is supplied with a pressure reducer, and the regulator starts closed.
How do I test a liquid or gel sachet without immersing it? Run a dry test with a white paper towel under each sample, seal under test facing down. Product that crosses a channel under vacuum leaves a stain or wet spot. Use a longer hold than for gas-filled packs, validated with known defects. A clean towel means no leak was seen under the test conditions, not that none exists.
Which chamber fits stick packs and stand-up pouches, CDV2 or CDV3? The CDV2 (280 × 200 × 200 mm / 11 × 8 × 8 in) fits sachets and stick packs. The CDV3 (450 × 300 × 250 mm / 18 × 12 × 10 in) fits stand-up pouches and gives more floor area for several units per cycle. Leave room for inflation, water and grid. Send DVACI your pack dimensions and it confirms the model.
Is the pouch leak test destructive? Mostly yes. Immersion wets the pack, so many plants scrap it. Internal pressurization punctures it. A dry test leaves a pack that passed untouched and dry, and your QA decides whether it may return to stock. Plan your sample size around the packs you will lose.
Does a pouch leak tester prove my package is airtight? No. Bubble emission and dye methods are probabilistic under USP <1207.2>: the probability of detecting a given leak is below 1. A passing result shows that no leak was observed with your validated vacuum level, hold time and procedure. The test is one documented element of a package integrity program, not a proof of tightness.
Request a quote for a pouch leak tester
Send the package type, dimensions, whether it has headspace, whether contents are dry or liquid, and your daily test volume. DVACI recommends the chamber and module and sends a quote within three business days of receiving the information. Installation, training, IQ/OQ/PQ documentation and traceable calibration are available.
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