Convert a gas barbecue grill from natural gas to propane or propane to natural gas with orifice plugs. Generally if we have to convert an orifice fabricated for LP use into an orifice that will burn NG all we need to do is determine the correct size and drill the orifice. This is because LP as a vaporized gas has a much smaller mass than NG and this means the LP orifice will have a much smaller hole than the same BTU’s for NG which needs a much larger hole in the orifice. Using the regulated pressure, BTU’s per burner and an orifice drill bit we simply check the chart to determine the right size and drill the orifice to make the smaller LP opening into a bigger NG opening.
If we are converting a BBQ grill from natural gas to propane we will normally have to remove the NG orifices and replace them with LP orifices because the larger hole cannot be made smaller. Unfortunately a new orifice drilled for LP gas is not always available for every barbecue grill on the planet. Necessity is the mother of invention — if we are converting a barbecue and cannot locate new orifices we have to figure out how to make that larger NG hole into a smaller LP hole.
This Spud style orifice is from a NG barbecue grill and it is not a brass fitting of a size that we have new orifices that can be drilled to whatever size we want them to be. In order to convert this barbecue to use liquid vaporized propane we need to make the hole in the orifice smaller.
If we are able to buy a replacement orifice that can be drilled to the size we need that should always be the right move. Often finding a replacement orifice is not possible and because the valve and orifice can be fragile we need the size and threading to be exact. Using the original orifice is about as exact as we can get. When a replacement is not available we will ruin and then repair the original orifices to make the larger natural gas hole into a smaller propane hole for our low pressure appliances: barbecues, grills, fireplaces, fire pits, side burner ranges and smokers.
In order to seal the hole the first step is to get a brass orifice plug and match the cylinder tube of the plug with a drill bit. I use a “21” orifice bit which is Huge and only needs to be reamed back and forth a little bit.
Drill the Huge hole in the orifice. At this point the orifice is totally ruined if we do not plug it correctly because Nothing needs this big of an orifice opening. Drill the orifice taking care of the size based on the plug and being careful not to damage the threaded inner walls of the back of the orifice when working with small spud style orifices like this one in the picture.
Once we have drilled the large hole in the orifice we need to check it with the plug. Sometimes we’ll need a bigger drill bit or only need to ream the drill bit back and forth a little to open the hole. The plug should start into the hole but not go in easily.
Use a hammer to lightly farce the plug into the hole. Be careful not to hit the soft brass so hard we ruin the original orifice. I usually start with slight taps and work up watching the plug. Use a strong solid base; nothing ruins the strike more than a moving table or soft floor that will move when hit.
We also have to match the back end of the orifice with the large part of the punch. The small tip will be small enough for the back-end of the plug but as it increases in diameter note that larger diameter will be hit into the back of the orifice and will tear the brass threads if it is too bog to fit into the back opening. This punch shown in the image is a part of the kit and there are bigger punches but not smaller ones. When I need a smaller punch I use a small phillips-head screwdriver as a punch and spreader so I do not tear the orifice.
Remember the whole reason we’re going through this process is because replacement orifices are not available and we have to use our original orifices. Check twice so you do not rip the orifice and have to replace an entire valve simple to change the orifice.
Once we have chosen a good punch we need to get the plug into the large hole we drilled into this spud orifice.
Use a hammer to force it through. If you over-drilled, deal with it by testing at the end and using a plumbers putty when you replace the leaking plug. Optimally we want the plug too tight to be able to be placed by hand. We want it to be forced with a hammer so it is as tight as possible.
Makes sure to sink the plug into the orifice completely so the head is tight against the head of the orifice. We want the enlarged part of the plug to completely hide the hole we drilled so no gas can escape sideways later.
Once the plug is tightly inserted from the front of the orifice it feels tight but years of use can change that. The next step is to solidify the plug by using the spreader punch. Insert the punch you chose from the back of the orifice inserting it into the hole of the plug. Smack it with the hammer, hard enough to spread and possibly tear the brass. Place the orifice upside-down so the rounded plug head is on a solid floor. This way when we smack the back side of the plug hard we are not risking dislodging the plug from the orifice. The tubular back-end of the plug that is inside the orifice will be forced to spread and pull the head tighter against the outer front of the orifice.
I can only barely tell with the small orifice because it is so tight inside the back end of this spud. The left image is the plug simply pressed into the orifice. The right image is the plug spread to tighten the plug into the orifice tight enough to keep it there forever (or until we have to change it again and remove it by drilling through the plug).
Once the plug is forced tight into the orifice the result is a orifice with the threading we require to attach to our barbecue grill control valve but without a much-too-large hole drilled in an orifice designed for use burning natural gas. Now our orifice is sealed and we can drill the orifice with what ever size orifice drill bit we need.
Determining the orifice hole size means knowing the gas type, amount of regulated gas pressure and BTU’s for each burner. For instance LP standard regulators will regulate vaporized liquid propane at 11″. Like any plumbing gas pressure is generally measured in pounds per square inch. Gas fireplaces, barbecues, grills and smokers use a very low-pressure setting well below one pound per square inch so we measure the pressure in terms of water-column displacement. In a manometer the gas pressure is attached to a tube of water and the pressure is only strong enough to push the water so far in the tube. Natural gas has more mass but is usually regulated between 2 inches and 9 inches whereas LP is always regulated at 10-11 inches for low-pressure appliances.
Orifice sizing charts will be in columns of Inches starting with 2 and moving up to 11 inches for LP gas. The rows of the chart will show BTU’s. We find the BTU for the burner and match the proper BTU in the column of regulated gas pressure we’re
using and that tells us the size of the orifice we will need.
As Always if we need assistance, contact Majestic Grill Parts.