Is an IP67 sealed protective case good enough?

Answer: IP67 covers a 1 m, 30 minute immersion only, not pressure differential or opening life. Retest after two hundred closures and the decay figure often fails.

Silicone or EPDM gasket?

Answer: Look at temperature span and ozone. Above 120 °C span choose silicone; for sunny outdoor duty with moderate heat, EPDM lasts longer.

Can I copy groove dimensions from another case?

Answer: Not directly. Depth and cord diameter are a matched pair, and a compound change alters hardness and rebound.

What pressure drop counts as a pass?

Answer: Grade it by volume. Up to 20 L use 0.5 kPa, 20 to 60 L use 0.8 kPa, above 60 L finish with immersion.

How often should the gasket be replaced?

Answer: By closures, not by calendar. Inspection duty suggests 400 closures or two years; a rarely opened case can go five years.

How to Choose a Sealed Protective Case: Five Checks

Quick answer: The gap between two sealed protective case quotes rarely sits in wall thickness. It sits in gasket compound, groove depth and latch clamping force. Fix immersion depth, temperature range and opening frequency first, then check compression ratio and test method.

Where a Sealed Protective Case Specification Starts
Gasket Compound and Compression Set
Groove Geometry and the Sealing Line
What an Air Decay Test Actually Proves
Latch Force, Relief Valve and Temperature
FAQ

1. Where a Sealed Protective Case Specification Starts

Selection meetings usually end on one question: does this box have to survive being submerged. A sealed protective case is bounded by immersion depth, temperature range and openings per year.

Service condition	Number to write down	Structural choice
Rain and standing water	200 mm, 30 minutes	Single line, 5.8 mm groove
Overboard or pressure wash	1 m, 30 minutes	Deeper groove or twin lines
Hot cabin storage	70 °C, 8 hours	Silicone, not nitrile

A case opened more than four hundred times a year wears its gasket out before the wall shows anything.

2. Gasket Compound and Compression Set

The gasket is a consumable, and its life is read from compression set, not softness. To GB/T 7759.1 at 70 °C for 24 hours, silicone lands inside 25 percent and nitrile about 15 percent.

Sealed protective case: olive green closed body at an angle, three lid ribs, two latches open at the front, folding handle flat on the right

Choose by temperature window first.

Compound	Temperature window	Compression set
Silicone	−55 to 200 °C	≤ 25%
EPDM	−40 to 120 °C	≤ 20%
Nitrile	−30 to 100 °C	≤ 15%
Fluorocarbon	−20 to 200 °C	≤ 20%

Hold compression between 25 and 30 percent. Below 20 the lid tolerance cannot close the gap; above 35 the cord takes a permanent set at 70 °C. Accept cord at ±0.15 mm diameter.

3. Groove Geometry and the Sealing Line

An 8.0 mm cord in a 5.8 mm deep groove gives 27.5 percent compression. A 10.0 mm wide groove leaves the cord at roughly 87 percent fill, so material can flow sideways.

A 0.5 mm root radius and a 0.3 mm chamfer decide whether the cord is sheared. A sharp corner nibbles a notch over repeated closures, and a decay test finds it.

Lid flatness is held to 0.3 mm and parting-line mismatch to 0.2 mm. Ribs every 100 mm keep deflection low; at 160 mm spacing the middle of the lid lifts off the line under vacuum, which is where most leaks on a sealed protective case sit.

4. What an Air Decay Test Actually Proves

Pressure decay is the workhorse: charge to 20 kPa, hold 60 seconds, accept no more than 0.5 kPa. The vacuum version pulls to −15 kPa and allows 1 kPa of recovery within 30 seconds.

Sealed protective case: olive green body from the far side, square lid recess, two black latches closed, handle upright right, vertical ribs to the base

Sensitivity differs by an order of magnitude: bubbles locate a leak, decay suits batch sampling, helium reaches very small rates for stored cases. Condition samples four hours at 23 °C ± 2 °C.

Passing decay is not passing immersion. A sealed protective case can pass one and fail the other, since IP67 is judged at 1 m for 30 minutes with no visible water inside.

5. Latch Force, Relief Valve and Temperature

A latch should close at 90 to 120 N, spaced 250 mm along the lid. Too little and the lid lifts; too much and it bows a gap either side. Run a 0.05 mm feeler around the lid after assembly.

Two hours in a 70 °C cabin raises internal pressure, and the vacuum at opening pulls the gasket against the groove. A valve opening at 3.5 kPa releases it without letting water in.

Item	Control value	Purpose
Latch closing force	90 to 120 N	Even clamping
Latch spacing	250 mm	Limits lid deflection
Relief valve opening	3.5 kPa	Balances thermal pressure

Handles are rated at three times payload, so a 30 kg case must hold 90 kg static. At −30 °C the latch-to-handle junction cracks first.

Conclusion

The order cannot be shuffled: bound the condition, choose compound and ratio, lock the numbers with groove, latch and test method. Two acceptance lines, decay and immersion, beat one word for waterproof. What separates one sealed protective case from another is the figures a buyer can re-measure.

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.