Reply To: The use of a venturi and combustion blower fan to mix primary air prior to cumbustion

[ectofix]

I can only chime due to similarities between Convotherm and Rational. 
As you’ve mentioned, a Rational oven’s operating gas pressure can’t be measured with a manometer.  So, their tech manual delineates a procedure for adjusting gas flow by measuring CO2 and CO at the exhaust flue by using a combustion analyzer.  From my memory (I have to read up everytime I do this), the idea is to establish a target CO2 reading (listed in their manual) that represents a burner operating at optimum efficiency.  As such, CO would be at a minimum.  There’s more to it than that, but that’s the idea.
As for any affects of the combustion blower’s variable-speeds in my Rational ovens, once I’ve properly set up the burner’s combustion rate at MAX blower speed (again, per their manual), there’s a flexible draft tube connected between the blower and the regulator that (I think) provides feedback to the gas valve so it can vary the gas flow based upon the varying air flow.

There’s much to learn about combustion analysis, but I lack the experience to offer much more off the top of my head.  Indeed, I’ve worked on gas cooking equipment for twenty years and I’ve only had to have a combustion analyzer for just THESE ovens.  Yet, I’ve often wondered if furthering my knowledge on combustion analysis could serve as a means to fine tune other equipment…such as the setup in a KGL kettle.  I don’t recall Cleveland ever requiring that, so I’m just saying.
I think folks in the HVAC trades are more up-to-speed on the importance of combustion analysis than guys like me just doing hot side work.  Heck, HVAC techs take it another step further by “clocking a meter” to gain the MOST optimum performance from a gas furnace.  Jim Bergmann has some videos about that on YouTube.