I am in the process of assembling a heater to preheat WMO and or WVO for my boiler and my question is with regard my design and the temperature needed for combustion. What I am going to try is similar to Eric’s heater except I am not putting in an insert to preheat air (3/4” copper with couplers as spacer bushings for the band heaters). I am going to use a very similar design that I am going to put in place between the oil pump and my existing burner nozzle. It is basically an inline heater with only 3 inches of copper line to the nozzle from the end of the heater. I think there will be enough residual heat from the unit to preheat the nozzle assy also. When the burner cycles on, the electric oil pump will pressurize the entire assembly and out to the nozzle. The inline heater will be a couple inches below the nozzle to prevent oil from flowing freely out of the heater to the nozzle when the pump is cycled off. I am using three 150 watt band heaters to heat this unit.

Here are my questions:
1) Quite simply… Do you think it will work? I am wondering how it will do pressurizing all the oil in the heater cylinder, and then force through the nozzle assy. I am heating the oil after the pump as I don’t think that sort of heat should be going through the little electric pump.
2) I know you guys recommend 300 deg for the oil temp and you obviously know what you are talking about, but what is actually occurring at this temp? Does the oil not pressurize and boil out of the nozzle at this temp? At what temp does WMO & WVO actually start to boil? I just have a hard time seeing all the oil inside a heated cylinder not building up scary pressures or boiling out the end of the nozzle. Just some thoughts that I would really appreciate some feedback on. I will be putting this thing into action as soon as I get my snap discs in place.

I think I need to see some pictures of what you are building. Without seeing what you are doing, I can only say that in the past my experience has been that the reason for a large preheater is to have a mass of oil with enough residual heat so that once you start drawing on it, the temperature doesn’t drop. Smaller masses of metal just can’t keep up unless perhaps, you drive it with 240v. You lose me when you say that you are using your oil pump to pressurize the oil line out to the nozzle. Usually, the idea is to let the siphon nozzle’s air suck it up from a pre-heated tank of some sort, so again, maybe I’m not following what you are doing along side of what you are proposing. You haven’t mentioned the air feed at all.

Is that part of the project already completed? Good question: I don’t really know what temperature oil actually starts the roiling effect like water and begins to “boil.” I’ve gotten it up way past 300 degrees and it doesn’t “boil” unless something is dropped into it like freedom fries, water, etc. I don’t find it a problem to work around the oil at 275 degrees. You just have to respect it: it doesn’t “boil” at that temperature, but it will definitely bite you if have an accident and get it on you. I haven’t heard of any problems so far with hot oil creating a pressurizing effect on the preheaters and I haven’t seen anything designed into any of the commercial burners that addresses an issue like that. If your preheated oil tank is below the pickup of the nozzle, then it should not stream out continuously.You could do an experiment on a stove heating veg oil to see where it goes because I think it just starts smoking away.

Sorry for not being a little more clear. I am not working with the siphon nozzle yet. I wanted to take a crack at running heated WMO/WVO through my boilers factory nozzle before I go wild and completely modify the burner assy. The preheater as I described is ¾ copper and will have 450 watts powering it. The unit is about 8” long and I am sure it will have no problem heating all the oil going to my .75 gph nozzle. I have gotten it underway and will upload my pic’s to my own website (unless you want them in the forum folders) and post a link to them in the next few days. Thanks for your reply! My mind is a little more at ease regarding the oil temps.

 I have a bit of experience with burners. Let me throw this question out so your folks can pick it apart. Regarding preheating of the oil, do you really need to preheat the whole oil supply? Is it conceivable to just preheat the feeder pipe (similar to how a modern coffee maker works) so that preheated oil is delivered to the burner without going to the trouble and expense of heating the whole 250 gallons? …or, make a 1 or 2 gallon tank between the bulk supply and burner (but close to the burner) and just heat that?

Now I understand what you are doing! I have built both burners: the conventional nozzle and the siphon nozzle, so it is possible to burn wvo both ways. On the conventional burner setup someone (it’s nice to have a milling machine next to the washer and dryer) milled me a “aluminum brick” for a pre-heater that fits right over my existing oil pump. That stays at about 120 degrees using two cartridge heaters. (see the photos in my folder.) Then I have three collars with three 200 watt band heaters on them along the length of the nozzle tube going down to the nozzle. I control them with a Watlow digital temp controller and that is set on 278 degrees. On a startup I see a drop of between 10 to 15 degrees at the nozzle end, so that has to factored in as well. If you want to make it easy on yourself, get one of the Kagi air diffusers. Like night and day, although I think the center hole is an arbitrary size. This weekend, I’m going to make mine a tad larger to allow me to slide it a little further onto the blast tube. The further up it goes, the less crude buildup there is on the electrodes and the nozzle.