ESBE Thermic Valve - Piping Question

EricPeterson

Thanks for your help in the past - here I am, back with another question.

I have a converted gravity system with an atmospheric boiler, am looking for boiler protection, so have been looking at the Danfoss Thermic valve installed on the return. But I have a question concerning their attached piping diagram ("Gravity/Large Volume Hot Water Systems:").

Danfoss says: "The recommended piping allows the heat source to handle the returning water while providing heat to the system."

When the valve is closed, the left pump is cycling water through the boiler, and the right pump is separately cycling water through the system. No heat is being provided to the system. Once the valve opens, the left pump would be able to push water through the boiler and the system.

My question: <strong>what it the purpose of having the two pumps? </strong>One pump seems to me like it would be sufficient.

The only reason I can come up with is that due to the system head, the water would tend to flow primarily back to the boiler rather than to the system. But it seems like that could be adjusted using the flow control valve. I am just trying to keep things as simple as possible here.



Thanks,

Eric Peterson