Does an airtight plastic safety case marked IP67 need a pressure test?

Answer: Yes. The IP rating records water entry; the pressure test shows whether the gasket holds under differential.

How often should the gasket on an airtight plastic safety case be replaced?

Answer: Count cycles: 300 closures or 18 months, whichever comes first. Replace the cord if recovery passes two seconds.

Does a relief valve make an airtight plastic safety case easier to flood?

Answer: The body is one-way; risk sits in diaphragm ageing. Press the cap before each opening, and a normal return means it works.

How is tightness judged on site without a pressure gauge?

Answer: Close the case, stand it in hot water 30 seconds and listen for a faint inrush, then run the feeler gauge around the rim.

Airtight Plastic Safety Case Checks for 40 Days at Minus 20

Quick answer: An airtight plastic safety case is judged on three numbers: pressure drop under 0.3 kPa after 60 seconds at 20 kPa, gasket compression between 25 and 30 percent, and a 0.15 mm feeler gauge that will not enter around the lid.

Air Tightness Is Not Waterproofing and What Must Be Held
Gasket and Groove Dimensions You Can Measure on Site
Valve and Thermal Cycling from Minus 20 to 60 Degrees
Latches and Shell Stiffness Measured at the Lid Joint
Turning the Criteria into a One-Page Acceptance Sheet
FAQ

1. Air Tightness Is Not Waterproofing and What Must Be Held

A batch is closed at 20 °C, sails for 40 days, sees minus 20 °C in the hold and is opened at the destination. Whether the gasket held is a question only a pressure reading answers.

Waterproofing rates water entry; air tightness rates pressure retention. An airtight plastic safety case is holding a decay curve, which is a different claim from an IP number.

Level	Site criterion	Test	Common overstatement
Airtight	20 kPa held 60 seconds, drop ≤0.3 kPa	gauge and plug	IP marked, drop unmeasured
Watertight too	above plus 1 m immersion, 30 minutes	immersion tank	soft gasket, never seated
Equalised	valve opens at 0.35 bar	differential bench	valve body without diaphragm

The levels differ by groove depth and a valve, and most field rejections come from the second level sold as the first.

Plug the valve port, apply 20 kPa and watch the needle. A 0.1 kPa fall in a minute is normal absorption; 0.4 kPa is a leak.

2. Gasket and Groove Dimensions You Can Measure on Site

Judging the seal needs no teardown, only a caliper and a depth gauge reading groove width, groove depth and cord diameter.

Airtight plastic safety case: a closed black blow-moulded case on a workshop bench, three more of the same body staggered behind, timber racks beyond

Point	Tool	Acceptable	What failure looks like
Groove width	caliper	6.2 mm ±0.2	wide, the cord wanders; narrow, it will not seat
Groove depth	depth gauge	4.1 mm ±0.1	shallow, the lid stands off; deep, nothing compresses
Cord diameter	caliper	5.5 mm ±0.1, 55A	soft cord recovers slowly, hard cord will not bed
Joint	eye and pull	45 degree mitre, no step	butt cut leaves a 0.3 mm gap

A 4.1 mm groove with a 5.5 mm cord gives 25.5 percent compression, mid-band. Under 20 percent it will not seal; over 35 percent it takes a permanent set within three months.

The joint is the easiest place to be fooled. On a mitred case it sits at mid-run with 5 mm of tail each end for thermal movement.

3. Valve and Thermal Cycling from Minus 20 to 60 Degrees

A lid of 1,000 square centimetres facing an 80 °C swing carries about 0.14 bar, or 14 kg of extra force to open. Without a relief path, an airtight plastic safety case puts that on the latches and the wrist.

A valve is not a free upgrade either. Set cracking pressure at 0.35 bar; below that it leaks in transport, above it may as well not exist.

Four checks settle a valve in ten minutes:

Press the cap and time the return, under one second
Hold the diaphragm to the light: no cracks, no tackiness
Bake at 60 °C for four hours, open at once, listen for inrush
Freeze at minus 20 °C four hours, open without tools

Steps 3 and 4 compress a sea voyage into an afternoon; a slow inrush means a stiff diaphragm.

4. Latches and Shell Stiffness Measured at the Lid Joint

The joint gap mirrors stiffness. Close an airtight plastic safety case and run a 0.15 mm feeler gauge around the rim; wherever it enters, that section is not sealing.

Airtight plastic safety case: an open silver hard case on a studio bench, egg-crate foam in the lid, two black inserts with square cavities

Check	Tool	Limit
Lid joint gap	0.15 mm feeler gauge	no entry anywhere
Mid-span deflection	straight edge and 30 kg	0.8 mm or less
Latch opening force	pull gauge	120 to 200 N
1.5 m drop, six faces	concrete	latches shut, lid not sprung

Latches set too tight hold the gasket past 35 percent and it stops recovering; too loose, and the gap opens first at mid-span.

Measure the gap again after five cycles; that reading beats the one out of the carton.

5. Turning the Criteria into a One-Page Acceptance Sheet

Inspect within 24 hours of arrival, after which responsibility is no longer provable.

Five lines are enough:

Pressure drop: 20 kPa for 60 seconds, record start and end
Compression: three readings of depth and cord, averaged
Valve action: return time, plus opening feel after hot and cold cycles
Gap: 0.15 mm feeler gauge around the rim
Latch force: pull gauge between 120 and 200 N

Draw 20 units from a 500 unit lot at AQL 1.5, always testing the corners and the long-side mid-span.

Conclusion

The quality of an airtight plastic safety case does not live in a datasheet; it lives in a caliper, a depth gauge and a pressure reading on the floor. Groove depth, cord, compression, gap and valve action, five numbers that agree, carry a 40 day voyage.

Ask an airtight plastic safety case supplier to let you measure; the answer tells you most of what you need.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.