I would hazard a guess that every one of us who’s built a siphon burner has tried this: what happened to me was that the wvo fired up and ran fine outside the chamber but once installed it ran too rich and created a lot of black smoke. In my case, the temperature differential inside the burner changed so quickly that the chamber has no where to pull the fresh air from.
I remember others having similar results and once I turned on the blower then it was fine and I had another helpful variable to use to control the air flow/ cone/ pressure. I’m switching out my 3450 rpm motor on my siphon nozzle and installing the 1750 spare I have just to see what happens.
Wether or not we all have to eventually use a lower rpm blower is another question. In my case, having a hot flame cone didn’t mean that the heat got transferred to the heat exchanger. (I have a forced hot air furnace, not a boiler)
One of my trials was to take out my blower and wrap black electric tape around half of the squirrel cage fan and made good increase in the flame size but had to remove it later in case the tape came loose, so running a slower motor like Jesse has done would make sense. In my case I fear loosing my compressor speed. So far it is the only thing that that is not giving me any trouble but might have to try it just to see what will happen.
Yes, it will run without the blower. I have run both my siphon nozzle and pressure assisted nozzle setup this way. I will say though, that I get a better combustion and a cleaner burn with just a little amount of air being provided by the blower. It provides enough turbulence to create a better swirl at the diffuser which will provide more of a complete combustion. Also if you have a chimney that needs a little help getting the draft started prior to a nice hot draw from a hot heat exchanger, you’ll need the blower.
Oil needs about 30 CFM of combustion air for each 100,000 BTU/Hr input. The atomizing air in a siphon nozzle is about 1 CFM for each 100,000 BTU/Hr. So the blower should be supplying well over 90% of the combustion air. Leaks around the blast tube or inspection doors cause excess uncontrolled combustion air. All of the combustion air should come from the blower, not from leaks. There are several ways to reduce combustion air to match the oil flow in a WVO conversion. 1. Block off the air shutter and only use the air band. 2. Block off the air band and only use the air shutter. 3. On a Beckett AFG ( and probably on the AF also) you can use the “Low Fire Baffle” to restrict combustion air. The “low Fire Baffle” is often the best way since it gives the most stable air flow, least affected by chimney draft.