Ancient Gas modulating valve

haaljo

Was talking this morning to retired mechanical engineer as to his heating system at home. He has hot water/gas. The original very old boiler was replaced 10 years ago. His eyes got dreamy desciribing a modulating gas valve that was part of the old boiler. He said it was a large 2 foot cube and modulated the gas intake based on "load" (but not outside air). He smelled gas from the unit and that motivated him to replace the whole system. Still misses it.

I was curious as to what the device was and why and by whom?

Mark Eatherton

Probably a Honeywell Modutrol...

They take up about that much space. They require a special floating control.



Not modulating the air, and only modulating the fuel sounds like an interesting proposition, until you see what affect it has on the combustion of the fuel, then it doesn't make all that much sense. If you can't modulate the secondary air, then the combustion numbers go upside down. there are also limitations as to how low you can go with fuel input before you start flashing backwards into the burner assembly, and if that happens, the CO will go off the charts.



ME

Tim McElwain

Those old modulating controls

would both modulate the gas and air together by using a movable offset series of connectors to the secondary/primary air door.They were going way back gas actuated systems.



There was also another version called the Republic Gyroscopic burner which would vary gas input in stages from high to medium to low and at the same time open and close the air doors.



Some of this is similar to commercial mod motor systems seen in recent years.



All of these required very patient and careful setup and needed to be serviced annually. We would actually when needed take the gas valves apart and replace the diaphragms. Service techs carried a bunch of different sized diaphragms in wax paper with oil to keep them pliable, they were made out of leather.

haaljo

He probably knows it modulated air as well.

I meant outside air (temperature) with regard to what input gizmo used to determine levels. I asked if outside air temperature was involved (no).  Sorry for the misunderstanding. It so happens on stricty steam "brianj"  posted recently about installing a two level gas valve as a retrofit on a steam system for savings. There wasn't any relplies but I was intrigued.

Thanks for your replies. I'll let him know.

(This is engineer was into controls more at industrial level - power plants, water treatment plants...really liked that thing he had on that old boiler.