The 6″ fill cap on top of an IBC comes in two flavors: vented or sealed. Sometimes people order the wrong one. The wrong one creates a small problem that is annoying to fix in the field.
Vented
A vented cap has a small one-way valve that lets air in or out as the contents expand and contract. This matters for liquids that breathe with temperature — most water-based products, glycols, edible oils — because the tote is rigid and the contents thermally expand.
Use vented when:
- The product is water-based or edible-oil-based.
- The tote will see significant outdoor or unconditioned-space temperature swings.
- Discharge will happen by gravity through the bottom valve (air needs to replace the displaced liquid).
Sealed
A sealed cap is airtight. Use it for products that should not see atmospheric oxygen, products that are volatile, or products that need to maintain a small headspace pressure.
Use sealed when:
- The product is solvent-based (and you do not want vapor escape).
- The product is oxidation-sensitive (some adhesives, some pharma intermediates).
- Hazmat shipping requires it (most hazmat classifications want sealed).
- Discharge will happen by pump or pressure, not gravity.
The small annoyance
A vented cap on a hazmat shipment will sometimes get refused at the dock. A sealed cap on a gravity-fed water tote will cause the discharge to slow to a trickle as the bottle deflects inward. Neither is a disaster. Both are an unnecessary inconvenience. Order the right one.