For a DIY griddle project I'm working on I need a propane burner that will heat up the cooking surface, I thought the build of the burner would make a good Instructable. Buying a burner was out of the question as the size and power I require is not available of the shelf. If you need to replace or repair a BBQ burner this might help you as well.
But a warningfirst, playing with propane is dangerous, so if you decide to try this you do so at your own risk and peril. At minimum wear safety glasses, gloves and non-flammable clothing. Also do this in a very well ventilated area, outside or in an open garage, you don't want carbon monoxide poisoning.
Step 1: Materials and Tools
This is what I used but other materials could be used as well depending on the application:
- 1" x 1/16" stainless steel tubing (could substitute this with regular steel but stainless will last longer)
- 3/4" to 1 1/2" black iron reducer fitting
- 1/8" brass NPT pipe nipple
- 1/8" brass NPT end cap
- 1/8" ball valve rated for gas
- 3/4" steel bar stock
- Low pressure BBQ regulator and hose (depending on how many burners you hook up you will need to increase the capacity of the regulator)
- Flare fitting to go from the propane hose to 1/8" NPT thread
- Propane Tank
- PTFE tape or pipe dope
- Drill and Drill bits
- Small Drill bits (1mm or 1.2mm) - you can get a set off amazon if you can't find them locally
- Tap and Die set (8-32 tap and 1/8" NPT tap)
- Welder with cast iron welding rods or MIG Welder with stainless steel wire (this makes things easier but it is possible to braze the parts together as well with a propane torch)
- Bandsaw or hacksaw
- Center punch
- Angle grinder with cutting disc
Step 2: Theory and Design
So lets talk about theory, at least in my layman's terms:
This burner design works off the venturi effect, as gas is being forced out through a small orifice mounted at the end of the burner, it pulls air along and mixes inside the burner tube. The mixed propane and air then is forced out of the burner holes or slots and when ignited it burns.
Propane needs to mix with air to burn at a specific ratio, but with trial and error I was able to get the burner to burn with a nice blue flame. If you get a flame with yellow or orange, it means that there is un-burnt fuel and not enough air has mixed with the propane to get proper combustion. The size of the orifice hole is very critical to the size of the tube, if the tube is too small and the orifice hole too large you get incomplete mixing and incomplete combustion.
For this design I tested many different orfice holes, from:
- 1/32" - too small - very small blue flame
- 1/16" - too big - lots of yellow but a very powerful flame
- 0.8 mm - too small
- 1.0 mm - just right - no yellow flame
- 1.2 mm - just right with a bit of yellow but a very strong flame
I landed on a 1.2 mm orifice hole.
Step 3: Video of the Construction of Burner
Check out the video for how I build the burner, the written steps follow:
Step 4: Orifice Assembly
The orifice assembly is made from
- 1/8" brass NPT pipe nipple (length is dependent on the application)
- 1/8" brass NPT end cap
- 1/8" ball valve rated for gas
- 3/4" steel stock
The center of the 1/8" brass NPT end cap was center punched and then drilled out using a 1.2mm drill bit, cutting oil was used too. This hole is the orifice and propane will flow out from this hole at high velocity.
Also pro-tip, if the drill bits are too small for the chuck of your drill use some metal tape and wrap it around the drill bit so it will make the shaft large enough to be grabbed by the chuck.
Center punch the 3/4" steel stock and drill a hole that corresponds to the 1/8" NPT tap. Using lots of cutting oil cut threads into the hole. This hole will thread the 1/8" brass NPT pipe nipple. Once the pipe nipple has been threaded through the hole, cap off the opening of the tube with the cap that has the orifice hole drilled in from a previous step.
Thread the ball valve onto the other end of the nipple. Be sure to ensure a leak free seal between all the fittings by using PTFE tape or pipe dope to seal the threads.
Step 5: Building the Burner Tube
The body of the burner is made from a piece of stainless steel tubing, stainless is really hard to work with as it work hardens. I first was going to drill burner holes in it but it would take far too long and far too much work so I decided I would cut small thin slots in the tube spaced 1cm apart for the burner "holes". I used my portable bandsaw and made short work of this but a hack saw could be used too.
The end of the stainless steel tube was heated and then bent closed in a vice. This allows the burner tube to be crimped and "capped" off, making a flat spot where a hole can be drilled and used for mounting the burner. The end of the tube was welded shut after crimping (this could be brazed as well).
Next the tube was welded on to the 3/4" to 1 1/2" black iron reducer fitting, the reducer fitting makes for a great burner intake for air and mount for the orifice. Two 3/4" steel tabs were welded on to the sides of the reducer that were tapped with a hole (3-32 bolts is what I used) to accept a bolt for mounting the orifice assembly. Again if you don't have access to a welder this could be brazed and the holes could be tapped directly into the end of the reducer fitting. I chose to weld on some tabs as it made it easier to work with.
A note about welding the black iron reducer fitting: these fittings are typically cast iron which do not weld very well or easy. Since I am just tack welding, it's not really an issue, also the cast iron should be preheated before welding. I am using a MIG welder with stainless steel wire, which I have heard that can be used to welding cast iron. So far I have had no issues with cracking. A nickle welding rod can be used too.
Line up the orifice of the orifice assembly so it's in the middle of the 1 1/2" opening of the reducer fitting, you want the propane to shoot straight down the burner tube so it can mix with air, clamp in place and mark the holes with a marker. Holes were drilled into the orifice assembly that match the steel tabs with the tapped holes so the orifice assembly could be bolted to the reducer fitting.
Step 6: Hooking It Up and Testing
To hook up the burner to the propane I used a fitting that went from the flare fitting on the propane hose and regulator to 1/8" NPT threads, in my case the ball valve. This will depend on the fitting you used so just use what I have done as a guideline, check your local area for a propane supplier or fitting shop and they will be able to get the proper fittings for you.
The propane regulator I used was low pressure one for a BBQ, it needs to be large enough to handle the capacity of the number of burners, in this case I sized this regulator to 80,000 BTUs, more than enough. It's better to have excess capacity than not enough. Remember the flow rate of the regulator is different than the pressure it can provide. Low pressure propane regulators (less than 1 psi) are very common and are plain gray or silver in color, a high pressure regulator is red in color. An adjustable high pressure regulator could be used as well but it depends on how forceful you want the flame to be.
Clamp the burner securely into vise or table before testing.
Turn on the propane on the tank and open the ball valve 1/4 of a turn ,you should hear gas flowing, using a BBQ lighter ignite the gas flowing from the slits cut in the burner tube. The whole burner should light, if it doesn't turn up the flow of gas. There should be a nice blue flame if everything is working properly. Trying adjusting the flow of gas and see if the flame is burning correctly, it should be blue when turned up low or high. If it isn't try changing the size of the orifice or the position of the orifice assembly.
With this design one could make a large burner provided you find a tube that is large enough to allow for proper mixing of the propane and air. Also remember a stainless steel burner tube will outlast regular mild steel but mild steel can be used as well especially if you are doing a proof of concept.
Good luck and be-careful!