Figure 3-46-CD

Liquid entering a chamber, not a stop-valve.

The contact angle on all surfaces is 50 degrees, so Concus-Finn filaments do not form. But the walls are high enough and the contact angle low enough that the liquid can fill the chamber. There being no step on the bottom at the entrance means the contact line has no problem advancing into the chamber enough to get the filament tips past the corners and into the chamber.