Basic Burner throttling test using orifices

I figured I’d share my setup since its slightly different than what I’ve seen others do…

I grabbed a couple of asco solenoid valves on the cheap and fitted up my propane hookup to “modulate” my burner (BG12) to run low, medium and high heat settings. In terms of setup, The main propane supply splits to feed each asco valve which also has its own orifice in line. The orifice on valve 1 is smaller than the one on valve 2. The 2 lines then rejoin and feed the discharge orifice that threads into the burner. Modulating heat stages: Valve 1 energized only = Low Heat (46%), Valve 2 energized only = Med Heat (77%), Valve 1 and 2 energized = High Heat (100%).

I’ve noticed a lot of people use needle valves which I’m sure work great, but I wanted something that was more permanent so I went with the orifice setup. I want to set my pressure and be confident that my flows are correct and repeatable. A couple of lessons learned:

I didn’t really think through the design and originally sized the 2 orifices to meter flow without using the (3rd)discharge orifice. This is where I’ve seen others have problems. These burners rely on the venturi effect, so the discharge velocity is key. So basically I was metering the fuel fine but without the discharge orifice, the burner wasn’t drawing enough air to get a good flame. The result was the large yellow flame seen in many videos. So I added a discharge orifice that was approximately the size of the original and bumped up the supply pressure and all was good.

I found some cheap ($4) threaded orifices by googling “orifice hood” and got the size 70 since that was the smallest orifice I needed. I didn’t want to do the trial and error method of sizing the orifices so I put together a matlab/Simulink model with a simple gui to get the sizing dialed in. Feel free to ping me if you are interested in the code(or even better, if anyone can package the combined matlab/Simulink routine into a single standalone executable for all to easily enjoy that would be sweet. I have matlab coder installed but haven’t had time to hack through it.) In the end I used the following orifices and run at ~4.5psi:

• O1 = size 72 (0.025&#8221
• O2 = size 65 (0.035&#8221
• O3 = size 56 (0.465&#8221

Final thoughts, This method could also be used to run multiple burners that need varying supply pressure (within reason) but are fed from a common header (such as a BG12 for MLT and BG14 for HLT). As long as the stock discharge orifice is used, an orifice can be added in series upstream to meter the flow based on a set supply pressure.

Now that the hard part is done, time to wire my ignitor and controller up. Ignore the mess in my garage and the labels on the board I was using test the valves. This was one of those quick and dirty tests. (Although I did a pressure test on the manifold prior to connecting.)



View attachment Burner.mov

You beat me to it! I'm designing a new stand right now and for my mash tun I'm doing nearly the exact same thing. I'll be using natural gas and using two valves to supply the burner. One unrestricted for heating strike water and the second throttled back for maintaining mash temperature during recirculation. I often forget to turn the burner down after mashing in and I don't like the high burner firing on under my mash, so the dual feed valves will fix this.

JonW said:

You beat me to it! I'm designing a new stand right now and for my mash tun I'm doing nearly the exact same thing. I'll be using natural gas and using two valves to supply the burner. One unrestricted for heating strike water and the second throttled back for maintaining mash temperature during recirculation. I often forget to turn the burner down after mashing in and I don't like the high burner firing on under my mash, so the dual feed valves will fix this.

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Nice! Let me know if you want me to run some numbers. Just need your range of supply pressure, burner model, total output (btuh) and prefered turndown in btuh or percent of total output.

BigBlock said:

Nice! Let me know if you want me to run some numbers. Just need your range of supply pressure, burner model, total output (btuh) and prefered turndown in btuh or percent of total output.

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Thank you for the offer, but I won't be getting so technical with mine. I'll have a manual valve inline on my second solenoid so I can set the restriction for the lower flow level. Since it's natural gas, the pressures are so much lower that it will be pretty easy to get the required flow manually.