Motorized and Thermostatic Manifold Mixing Stations
April 16, 2015

Do I need a hydraulic separator on a manifold mixing station?

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!

Blog post comments
Keith Dunn
September 24, 2018


The return outlet of my hydraulic separator requires an O ring fitting which the return valve tailpiece has. In my setup I do need the separator, the return valve tailpiece does not fit on the mixing valve body. All of the Caleffi information does not show an O ring fitting or that the tail piece has the be replaced. Am I missing something?


edward Redmond
August 01, 2019

I'm installing radiant floor heating in my house 6 zones with two circulators and 2 manifolds. The Boiler has it own Circulator loop.

My question is ---------

do you sell this hydraulic separator separately?

if I use 2 T's should i put in check valves on the secondary side?


August 02, 2019

Hi Ed,
The little separator that is on the 172 Series manifold mixing stations is available with the pump and mixing valve in a sub-assembly; it's not available separately.

Anthony mercurio
April 05, 2020

We Just installed one of these mixing manifolds for the first time, how do we purge the air? I feel as if when we bleed the water is coming thru H fitting directly to return side of manifold & not thru our individual loops. We closed all return loops & we still get flow thru bleeder hose. What are we missing?
Thanks, we use a lot of your products, this manifold is a great time saver & looks great... I truly hope I’m missing something simple on purging.


In reply to by Anthony mercurio

April 07, 2020

With the mixing station you will find the return elbow will allow water to bypass the mixing valve to the return side of the manifold. You may need to close the supply valve at the top of the manifold and purge the loops backwords through the ruturn manifold and out through the supply purge point. Or flush the manfold with water in the top purge point and out the return purge point to get air out of the individual circuits. If you have other questions you can call into technical support anytime.