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hydraulic air separator

Brad White
Brad White Member Posts: 2,398
Do you mean a hydraulic separator or an air separator? Two different things, but I will assume you mean hydraulic separator.

When creating primary/secondary piping, the essence of this is to have two distinct hydraulic circuits interconnected such that the presence of flow or lack of flow in any one, will not affect flow in the other circuit.

Conventionally, this is done with closely spaced tees which have negligable pressure drop between them. These tees are matched to a corresponding similar pair on the second circuit.

For example, a boiler circuit at a higher temperature connected to a lower temperature radiant circuit. The bridge piping between the two passes the hotter boiler water into the cooler radiant circuit in a <i>controlled</i> manner. However, flow happening in one, without that control, will not affect the other.

The hydraulic separator (also called a Low Loss Header) is a large vessel which does the same thing and remarkably well. Typically primary water enters a top connection and flows across to the outlet connection serving the secondary circuit(s).

The return water, conversely, enters the lower secondary side. At this point, the water has a choice based on which circuit contributes higher flow. Typically in condensing boilers, the secondary or cooler circuit moves more flow. Thus the cooler return water rises to blend with the hotter primary water to be recirculated. The remainder of the cooler return water goes back directly to the boiler in exactly the same quantity as enters from the boiler.

These devices can also serve for venting of air and containment and drain-off of system debris.

That is one application. Caleffi has a publication perhaps on their web site called "idronics" plus other literature that tells much more about these amazingly simple effective devices.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

-Ernie White, my Dad


  • Jeff Anderson
    Jeff Anderson Member Posts: 5
    hydraulic air separator

    Can someone explain the purpose of using a hyraulic air separator, what is the main use for these items?
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