Why airless bottles fail QC:
the four tests and what the numbers mean.

Why airless has its own test sheet

An airless bottle adds a mechanism to the usual checks. The pump group is engineered as a one-way seal: each stroke expels product and blocks air from flowing back, the bottle interior drops into low pressure, and atmospheric pressure pushes a piston up from the base to follow the product. The friction between that piston and the inner wall governs both air-tightness and travel. Too little and the seal leaks; too much and the piston stalls. Each failure below is that mechanism going wrong in a different place; the full sheet is on the airless, pump and sprayer specifications reference.

Failure 1 — piston fit

The first parameter a partner factory qualifies, because it decides whether the other three tests can pass at all. Two checks. Static: cool the body 4 hours after moulding, assemble the piston, fill with water and stand 4 hours; there must be felt resistance on the piston and no water passing it. Dynamic: stand 4 hours, fit the pump, dispense to empty; the piston must rise cleanly to the top with the contents fully expelled.

What a failure means. Water past a static piston is a body wall outside its fit-critical tolerance (≤0.5 mm on mating dimensions), a piston in the wrong PP grade, or a body assembled hot before it had shrunk to size. A piston that stalls on the dynamic test is too much friction, usually a wall taper or an out-of-round body; the consumer sees a bottle that stops pumping with a third of the product inside. Neither is fixable at the filling line.

Failure 2 — vacuum leak

The filled bottle is laid on its side and inverted on white absorbent paper inside a vacuum chamber. There are two levels: the line quick check at −0.05 MPa for 5 minutes, which an operator runs during production, and the full test at −0.08 MPa for 15 minutes with weight loss ≤0.5%, which goes on the inspection report. Standard emulsions are tested at −0.06 MPa, volatile formulas (ethanol, essential oils) at −0.08 MPa. Any trace on the paper fails.

A leak at the pump collar points to the gasket: NBR and TPE gaskets swell in oils and soften in high ethanol, and a low-surface-tension oil serum will creep past a seal that holds water perfectly. A leak at the inner-outer joint on a composite bottle points to the snap fit, checked by pulling the collar-to-outer assembly at ≥50 N. If the same bottle passes on water and fails on your bulk, the gasket is wrong for the formula; see the formula × packaging compatibility matrix.

Failure 3 — dose

Dose is fixed by pump diameter, stroke and spring force, repeatable to about 0.05 ml once set (0.15–0.2 cc serum, 0.5–1.0 cc cream). The measurement: fill to nominal volume, prime with 15 strokes, weigh, press 50 continuous strokes, weigh again; the difference divided by 50 is the single-stroke dose, repeated three times and averaged. The specification is signed against that average. A single stroke may sit ±15% from nominal; the run average must be within 5–10%.

Dose drifting low across the run is almost always the seal at the glass or steel ball under the spring: if it leaks, product flows back into the housing on each stroke, suction drops, and the pump starts "losing" doses. A loose actuator-to-valve fit produces the same symptom plus resistance at the nozzle. Both are visible at incoming inspection on the pump groups, which is why pumps are sampled as a component before assembly. A thick cream of 2,000–50,000 mPa·s needs a 0.5–1.0 cc high-viscosity pump and a piston-travel check with the actual bulk, not water.

Failure 4 — evacuation and priming

Evacuation is the promise airless makes to the consumer: the last dose is as full as the first. The protocol is to fill with a viscosity-matched liquid, pump until the bottle air-locks and weigh the residue; anything delivering less than 93% of the fill fails before production approval. Priming is the same promise at the start: bottle three-quarters full, first output within ≤8 strokes on coloured water or ≤10 on lotion.

Evacuation failures are piston failures under another name; priming failures are usually a pump qualified on water and never on the bulk. The most useful sentence in an airless specification is that priming, dose and evacuation are verified with the customer's actual formula on the golden sample.

The tests that are not about the mechanism

Beyond the four, an airless batch is held to the battery on the QC standards page: thermal cycling filled at 48 °C and −15 °C; drop from 1.5 m at 45°; 3M 600 / 3M 810 tape adhesion on decoration with hot-stamp loss ≤0.5 mm²; opening torque 0.2–0.7 N·m; colour against the golden sample under D65; heavy metals ≤100 ppm; sampling to ISO 2859-1 level II at AQL 0 critical, 1.0–1.5 major, 2.5–4.0 minor. Airless adds the 48 °C / 30-day compatibility soak of the assembled bottle in your bulk, ≥3 units per condition, weight loss ≤0.5% for volatile bulks; that is what qualifies the gasket, the PETG grade against your ethanol level and the spring against a pH under 4.

Where the tests sit in the order

Ask for the test sheet with thresholds before the deposit and the filled-in report before the balance. "Leak tested" without a pressure and a duration says nothing; "−0.08 MPa, 15 minutes, ≤0.5%" does. What else to check before paying is in how to evaluate a China packaging supplier; the minimums the tests attach to are on the MOQ index. Formats, capacities and finishes are on the airless bottles page, and the serum-cream-oil range planned together is on skincare packaging solutions.

Vella is a Guangzhou-based beauty packaging solutions provider, a sourcing partner working with vetted partner factories operating to ISO 22716 / GMP. For airless programmes the four tests above are written into the specification, verified on samples filled with the client's bulk, and reported at each inspection gate before the balance is released.

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