Thanks again for the information.
Does anyone know why plumbers install bypass lines without bypass valves? My coal and oil boilers are both done with a 1 1/4" line that run from the output of the boiler back to the return input (without valves). I saw other boilers done this way and I believe a member of this forum (bighouse) indicated his was done this way and his plumber called it an "equalization loop". I think this is what prompted Stoker-man to post this thread to help clear things up.
The odd thing for me is that I never noticed a problem with this when running my oil boiler. The return water would be the same volume and temperature returning to the oil boiler as it now returns to the coal boiler. The only thing I can think of is that the oil boiler is able to heat the water much faster than the coal boiler does and therefore I didn't notice the "short run time" of the circulator.
When a bypass line is installed in this manner without valves just how does the water flow thru the line? When the circulator is NOT running does the hot water at the top of the boiler flow "down" the bypass line and back into the return? Then what happens when the circulator IS running? Does any of the water flow from the return line "up the bypass" and back into the system, or does the hot water from the output of the boiler flow "down the bypass" and mix with the cooler return water which makes that warmer going into the boiler?
The old saying is, "Gravity Sucks". I guess this is true in physics and when you're trying to understand it!!!
I guess the bright side is it's wonderful if the power goes out and you're counting on gravity to distribute the heat.