PASSAVANT is a name used by the manufacturer ACO. To specify products related to drainage systems.
It seems that this cover is used as an advertisement for DANNHÄUSER.
The name R.DANNHÄUSER probably indicates the advertising/design company responsible for the advertisement (in this case its name is the same as the name of the company it advertises)
This cover is probably an advertisement, or a venture to note old businesses in the city.
An identical cover was photographed in 2025 by Hermann Klecker at Westenhellweg 73, 44137 Dortmund, Germany. This is a similar advertising project in Dortmund, probably carried out by the same company Click for a larger image
Translation of the text on the cover: DANNHÄUSER GMBH
EXCLUSIVE WORLDWIDE MANUFACTURING OF INDIVIDUAL MOTIVE SHAFT COVERS