boilerman
It probably is important to leave some bypass flow, and not to shut the bypass valve completely, if only because I could forget to open it when cold. I am not sure if the Danfoss passes any flow from the cold side when it is completely closed. I suppose an ideal valve would close the bypass as it opens the inlet - a job that the manual bypass valve does with my Danfoss setup. I guess that is what the Tamovar valve does, although I don’t know why there is a need for any bypass water once the system is up to temp.
The all-in-one units (Termovar Loading Unit, Laddomat, etc.) have a self closing balancing valve that does taper off the bypass water as the return water reaches the desired temp the thermostatic unit is set to hold. When the return water is above the 'setpoint' the bypass is completely shut off. It opens itself up when things cool down. No way I'd remember to do that.
If you already have your system setup and running with the simpler thermostatic loading valve (Termovar, Danfoss, and others) it might not be worth the extra money to get one just for the bypass shut-off feature. They are pretty expensive if you aren't starting from scratch. Here's the ACASO version:
(broken link removed) Acaso/LK eng/Termovar_Laddpaket_ENG.pdf
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