Why does case field airtight test use 0.3 kPa rather than more pressure?

Answer: 0.3 kPa is where a 25 L case matches a 12 mL/min leak under the 0.05 kPa criterion, and it keeps the needle legible. At 1.0 kPa the lid bows outward, the gasket is pressed tighter and small leaks hide.

The drop lands exactly on 0.05 kPa. Pass or fail?

Answer: It passes on paper, but repeat it once. Needle hunt is ±0.01 kPa, so the reading really spans 0.04 to 0.06; sign off only if the second run stays at or below 0.05 kPa.

Can case field airtight test run without a gauge?

Answer: Yes. Fill a 0.5 m clear hose to 30 mm and accept a fall of 5 mm or less in 60 seconds. Resolution is 1 mm, about 0.01 kPa, enough for the 0.05 kPa line.

On a failure, replace the gasket first or check the valve?

Answer: Check the gasket first: it causes over sixty percent of field failures and takes 6 minutes to confirm. Mask the valve and both latches, retest, and an unchanged drop confirms it.

How many cases can one crew test in a day?

Answer: Four minutes per case gives a nominal 120 in eight hours. Allow for repairs and paperwork and plan on 80, which fills the day once rework reaches 10 percent.

Case Field Airtight Test: Field Airtight Retest

Quick answer: Case field airtight test needs 0.3 kPa, a 60 s hold and a 0.05 kPa drop or less, and runs on a hand pump with a 0.25 class gauge.

Where the 0.3 kPa and 60 seconds come from
Reading a 60 s hold against a 0.05 kPa drop
When there is no air supply: three substitutes
Vacuum at −20 kPa and 5 mL/min to locate a leak
The three repair points inside 15 minutes
FAQ

1. Where the 0.3 kPa and 60 seconds come from

The bench gauge reads 0 to 10 kPa, one division per 0.05 kPa. At 0.3 kPa the needle sits on the sixth division and stays legible; at 0.1 kPa it sits on the second, where reading error eats half the criterion. That is why case field airtight test starts at 0.3 kPa.

The conversion is clean too: 30 mm of water equals 0.3 kPa, so a clear hose filled to 30 mm is a gauge when none is at hand. The 60 second hold follows line rhythm, since one retest takes four minutes and at 180 s a crew never clears 40 cases in a shift.

The threshold is back-calculated. A 25 L interior holds 74 mL of extra air at 0.3 kPa, so a 0.05 kPa drop equals 12 mL, or 12 mL/min across the minute. The figure is an equivalent leak rate, not a round number.

2. Reading a 60 s hold against a 0.05 kPa drop

Pressurise to 0.3 kPa, wait 10 seconds, then start the clock; those seconds let hose and case equalise, and skipping them turns settling into apparent leakage. Record the start value and the 60 second value only. The needle hunts ±0.01 kPa, and staring at it invents a trend.

Case field airtight test front view, black case open on grey, egg-crate lid foam, dark base foam holding a lamp and cables, two latches

Temperature is the largest field disturbance. A case moved from a 5 °C store into a 25 °C shop warms, its air expands, and pressure creeps 0.006 kPa per 10 °C within the minute, the same order as the criterion. Soak two hours until the shell sits within 2 °C of ambient.

Shell-to-ambient difference	Apparent rise in 60 s	Field correction
0 °C	0 kPa	Read directly
5 °C	0.003 kPa	Raise start pressure by 0.003 kPa
10 °C	0.006 kPa	Raise start pressure by 0.006 kPa, or soak longer
20 °C	0.012 kPa	Stop, soak 2 hours, restart

Touching the shell is the quickest rough check: colder than the palm means the case has not settled and the reading stays out of the log. Hose length counts too, since a 1 m hose holds 30 mL, 0.12 percent of a 25 L interior, so crews standardise on 0.5 m.

3. When there is no air supply: three substitutes

A compressor is usually missing on site. A hand pump, a hand vacuum pump and a water column each let case field airtight test produce a judgeable reading, with accuracy falling in that order.

The hand pump is the general tool: nozzle on the relief port, a three-way valve and a 0.25 class gauge in line, then 8 to 12 strokes to 0.3 kPa. Output is pulsed, so a 20 mL buffer bottle on the third leg settles the needle.

The vacuum pump reverses direction. Draw to −20 kPa, close the valve, wait 30 seconds and accept 1 kPa of rebound; it reaches failure modes that pressure cannot. Both directions need a seal, a 2 mm silicone square spring-clipped over the port, since a curled patch falls to zero in 10 seconds.

The water column is crude and dependable: 30 mm in a clear hose, 60 seconds, a fall of 5 mm or less, since 5 mm of water is about 0.05 kPa.

Method	Equipment	Pressure reached	Resolution	Where it fits
Hand pump	Pump, three-way valve, gauge, 20 mL buffer	0.3 kPa positive	0.01 kPa	Shop bench
Hand vacuum pump	Vacuum pump, gauge, seal patches	−20 kPa negative	0.5 kPa	Checking rim seating
Water column	0.5 m clear hose, rule, water	0.3 kPa static	1 mm of water	Outdoors, no power

Readings cannot be compared across methods: a hand pump may show 0.04 kPa where the column shows 6 mm, since a column has no buffer volume.

4. Vacuum at −20 kPa and 5 mL/min to locate a leak

Vacuum reverses seating. Pressure pushes the lid out and the gasket against the groove wall; vacuum pulls the lid in and draws the gasket toward the mouth. Each direction catches half the failure modes, so pressure passes or fails the case and vacuum finds where.

Case field airtight test shelf scene, four open cases on wood-grain shelving, a blue one with grey tray, two black, one red with metal fittings

Draw to −20 kPa, close the valve, watch for 30 seconds. A rebound above 3 kPa means one spot along the rim is not seated; a reading that stays under −10 kPa puts the leak at the valve or a latch.

Locating is a flow question. A 5 mL/min leak loses 5 mL a minute, invisible on the gauge but visible in soap, where a 2 mm bubble forms about every 10 seconds. A 5 percent dish soap solution works; a clean 20 seconds rules a spot out.

Segment isolation narrows the search. Mask both latches and the valve with 50 mm tape, retest after each, and the mask that changes the drop most holds the main leak. Three masks take 6 minutes, less than stripping a case.

5. The three repair points inside 15 minutes

A failed reading does not call for new parts. Ranked by frequency: a gasket rolled from its groove at 6 minutes, a flattened valve O-ring at 5, an offset latch seat at 4. Fifteen in total.

Lift the gasket loop out, clean the groove, press it back, then run a finger round the channel, where a bump means it is not seated. Fit the same O-ring size and tighten to 1.2 N·m. Loosen the latch seat at two screws, push it flush with the shell, retighten.

Point	Typical failure	Action	Time	Retest
Gasket	Rolled in groove, local lip	Lift out, clean, reseat	6 min	0.3 kPa positive
Relief valve	O-ring flattened, core sticking	New O-ring, 1.2 N·m	5 min	−20 kPa vacuum
Latch	Seat offset, low clamping	Loosen, align, retighten	4 min	Positive test, 3 cycles

Order cannot be reversed. A retest only says pass or fail; a repair has to say where, and one vacuum check often avoids a full gasket replacement. Retest within 10 minutes, while the new gasket settles.

Conclusion

Whether a site can run case field airtight test is a question of a closed loop, not of equipment. Confirm the shell is within 2 °C of ambient, fit a 0.5 m hose, pressurise to 0.3 kPa, hold 10 seconds, then pass the case at 0.05 kPa or less. Over the line, retest under −20 kPa; if the rebound passes 1 kPa, mask the ports in stages and back-calculate at 5 mL/min.

The decision table runs to three rows, and those rows settle three things: the criterion is not fooled by temperature, the leak is not fooled by pressure, the repair is not fooled by habit.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.