Identifying part in hydronic system

ohanasam · February 27

Can somebody tell me what the part is (circled in blue) on my heating loop? Thanks.

whatis.jpg

ScottSecor · February 27

Pressure bypass valve

ScottSecor · February 27

https://www.supplyhouse.com/Caleffi-519599A-3-4-Union-Sweat-Differential-Bypass-Valve

hot_rod · February 27

here is some info on how it operates

Screenshot 2026-02-27 at 11.42.33 AM.png

Screenshot 2026-02-27 at 11.42.55 AM.png

ohanasam · February 27

Thank you ScottSecor & hot_rod. Much appreciated.

ScottSecor · February 27

No problem. We used to use them often with single speed pumps (on off) with many zones.

ohanasam · February 27

https://forum.heatinghelp.com/discussion/comment/1889902#Comment_1889902

This is on a 5 zone heating system and an indirect. Three Taco 0010 pumps (DHW, Boiler & Heating). Just always wondered what the device was and now I know.

hot_rod · February 27

What size boiler, or heat load do you have?

That circ is a flat curve, ideal for zoned systems. In its sweet spot it would like to be flowing 12-20 gpm, mid curve

.

tcassano87 · February 27

cool info in this thread, I’ve never came across one of those valves

ohanasam · February 27

https://forum.heatinghelp.com/discussion/comment/1889911#Comment_1889911

Its is a 140k BTU boiler (heating 5000 sqft across two floors) at 7800ft altitude in Colorado

hot_rod · 1:49AM

140K input? X 84% is 117,000btu/hr. So that circ is about on the money for gpm capacity.

Identifying part in hydronic system

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