Caleffi Manifold Mixing Stations, such as the 171 Series and 172 Series, have a lot of impressive features. One of the best is a small hydraulic separator between the hot water supply/return ball valve connections and the mixing valve assembly. This "H" shaped hydraulic separator comes pre-assembled and can be easily removed when necessary.
Typical questions are: when do I leave it there and when do I remove it? The short answer is this: if you have a separate pump for the hot water supply system, leave it in. That way you will be hydraulically separating the 2 pumps, as you should. If not, take it out. That way the mixing station pump is circulating the water through the heat source and to/from the load.
Cody Mack, application engineer for Caleffi, does a great job explaining all this in the video below. As always, give us call or send an email if you have any questions!