February 06, 2015

Hydraulic Separation: Hot on Top, Cold on Bottom

Hydraulic Separation:  Hot on Top, Cold on Bottom

At first glance, piping a hydraulic separator - which has 4 connections - can be a little confusing.  Here is an easy-to-remember guideline to assure proper flow patterns and high performance from your Caleffi Hydro Separator, HydroCal™ or Sep4™.

Keep hot on top, cold on bottom. For a heating application this means connect the boiler hot water supply to one of the top connections and connect the secondary hot water supply to the opposite top connection. The boiler return connection is on the bottom, on the same side of the separator as the boiler supply. Across from the boiler return is the secondary return. Caleffi separators are not flow-directional; you can have the primary loop on the left and the secondary loop on the right, or vice versa (refer to Figure 6-19 from idronics™ 15:  Separation in Hydronic Systems).

For a chilled water application, the hot on top, cold on bottom guideline still applies. Connect the chiller water supply to one of the bottom connections and the secondary chilled water supply directly across. The warmer returns will be on the top.

Another way to look at it is this same guideline is this: if you have clockwise flow on the primary side of the separator, make sure you have clockwise flow on the secondary side. Counterclockwise in the primary, counterclockwise in the secondary. If piped such that flow directions are opposite, undesirable mixing will occur in the barrel of the separator which will affect the secondary temperatures and primary return temperature (refer to Figure 6-20 from idronics™ 15:  Separation in Hydronic Systems).

Hot on top will also assist in air separation; water's ability to contain air bubbles decreases at higher temperatures. Escaping air bubbles are then directly under the air vent where they are removed from the system.

Hot on top, cold on bottom piping for separators also assures maximum temperature differential (delta T) for the primary generator (boiler or chiller), which is highly desirable.

What are your comments? Thoughts? Let us know!


Last modified: 
March 31, 2015
Hydraulic SeparationHydronic Principles
Share on: