Question Bauer Varius questions

[Normygenius]

Hello wise friends. I just came into possession of this 1988 varius. It's in remarkable condition having been used by the local fire service as a back up.i got it as a contra for some work i did.
It's been converted to single phase from 3phase. I am hoping someone can explain the part shown with a blue arrow. Also is there a correct sequence for the 4 purges I.e. the 3 black knobs and the metal dial on top of that column.
I have the manual from Bauer bit its old and the drawings/photos are unclear. Many thanks in advance.

 

[NetG]

En bleu , forme section carré, séparateur dernier etage , la partie cylindrique contient la cartouche , les deux fonctions sont séparées sur ce modele de compresseur ancien.

In blue, square section shape, top stage separator, the cylindrical part contains the cartridge, the two functions are separated on this model of old compressor.

 

[Normygenius]

En bleu , forme section carré, séparateur dernier etage , la partie cylindrique contient la cartouche , les deux fonctions sont séparées sur ce modele de compresseur ancien.

In blue, square section shape, top stage separator, the cylindrical part contains the cartridge, the two functions are separated on this model of old compressor.

d'accord merci bcp....