The case of the tripped gas pressure switch, this Friday's case

RayWohlfarth

We found both upstream gas pressure switches tripped on two boilers. You probably have a pretty good guess what happened. In this weeks video, I talk about why they failed and how the gas pressure switches operate. What pressure should they be set for? Seeya on Friday at 6am EST

EBEBRATT-Ed

Gas was shut off. LP switch tripped.

RayWohlfarth

@EBEBRATT-Ed Yes sir that was it

RPK

In my 15 years of occasionally working on equipment that included high and low gas pressure switches, this is the only reason I’ve ever seen the low gas pressure switch trip.
I would be interested to hear some stories about intermittent trips that ended up in other diagnoses. I am that undersized meters or regulators, or undersized branch piping would be the main culprits.

I’ve also always assumed a few reasons why a low gas pressure switch might be necessary as a safety, but never had it formally explained by anyone. My first thought is that ignition would not be reliable and possible quite delayed with very gas pressure. Maybe a bunch of gas leaks out other burners before making its way to the ignition device or maybe pilot carryover burners don’t quite carry over to all the burners. Second thought is that really low as pressure could effect burner operation as flame pattern. The Venturi effect that draws in primary air on an atmospheric burner wouldn’t work at lower gas velocities from the orifices and maybe you would have flames occurring in locations where they were not intended. Does anyone have a textbook answer? What happens on power burners when gas pressure is too low?

RayWohlfarth

@RPK You get flame failures and the boiler does not have the same heat output. The flue gases could condense as the flames temperature is low