I'm presently intending for the single circulator pump to run 24/7. I guess I learned it from my current oil boiler and resistance boiler system, where the circulator never shuts off unless there is a power outage.
When all zone valves are closed the DPBV opens and keeps a circulation loop going to prevent dead-heading the pump, and to prevent local hot-spots from developing within the boiler.
Actually the DPBV is progressive. The more zone valves that are closed, the more fully open the DPBV becomes. When all of the zone valves are fully closed the DPBV is (or should be) fully open. When all of the zone valves are fully open the DPBV is (or should be) fully closed. Or so the theory goes. It is set by a spring tensioning knob that is scaled in PSI. Adjust for more spring tension or less until it does what it is intended to do, and then leave it alone to do its work. Mine is a Taco 3196, and it costs just under $50.
Initial set-up of a DPBV goes like this. If you know the "head" of your system you divide the head by 2.31 to get PSI. Then you dial in that PSI plus about 0.5 PSI more for safe measure on the DPBV's PSI scale (knob). Then you test it to see if it needs to be tweaked a bit. Feeling the DPBV's downside pipe for heat during differing levels of zone valve opening and closing is the tried and true method here. A rotometer (visual liquid flow indicator with a window and a spinning star wheel) on the outlet of the DPBV would be an expensive and exotic means to calibrate it to perfection.
Last edited by lsayre
on Fri Jan 28, 2011 8:50 pm, edited 1 time in total.