Non-pressure and low-pressure windows
Windows for vessels without excess pressure or with a small pressure difference; the limits differ between specific versions.
For vessels without excess pressure — silos, bunkers, storage tanks — light-duty fittings are used: threaded, clamp or cover-mounted. They are cheaper and simpler, but must not be used automatically where pressure or vacuum appears.
There is no common “safe” pressure boundary for the category: permissible conditions are defined by the construction of the specific product and the manufacturer confirmation.
What belongs to this category
- Threaded and clamp sight windows for non-pressure vessels.
- Windows on manhole and hatch covers with documented versions.
- Replacement discs for these constructions.
What does not belong here
- Pressure fittings DIN 28120/28121.
- Using a non-pressure window on a pressure vessel.
- Automatic conclusions about “permissible low pressure” without a source.
How to choose a non-pressure window
- Step 1
Confirm that the vessel really operates without excess pressure and vacuum, including washing and filling modes.
- Step 2
Check the medium for dusting and sticking — silos often need a wiper.
- Step 3
Clarify the temperature regime: external heat and solar heating count too.
- Step 4
With any doubt about pressure — consider the pressure categories.
Series and constructions of the section
The “Non-pressure windows” series examines typical constructions and their limits.
Sources
- ACIopen the sourceTechnical review: 2026-11-04