When a gas barbecue grill is being converted from natural gas to liquid propane or from liquid propane to natural gas there are 2 changes to the barbecue that have to be made. The regulators have to be changed.
Natural gas can be pressurized differently due to altitude, length of the gas line run and depending on how many appliances are on the same gas line. However, once the gas is coming into the barbecue grill the appliance regulator is usually going to regulate natural gas at two to four inches of water column. Because we are working with pressures less than one pound per square inch measuring the inches of water column displacement allows denominations of pressure.
Liquid propane can also be under different pressures but as LP gas comes into the barbecue grill it will always be pressurized to eleven inches of water column displacement.
In addition to changing the regulator when converting a barbeque grill from one gas type to another gas type the orifice on each control valve on the BBQ has to be changed. That means the side burner controls, rotisserie controls, the main BBQ valve controls, smoker controls, every control valve will have an orifice on it and every orifice has to be changed. LP gas is a solid liquid that vaporizes (boils) into a gas when it is being used in low-pressure appliances like gas fireplaces, fire pits and barbecue grills. A orifice for LP gas will be drilled with an opening determined by the BTU rating of the BBQ burner.
The image above shows hood-style orifices that screw onto a control valve. When installed into the barbecue the orifice will be inserted into the venturi tube of the gas grill burner and will spit gas into the burner to ignite. The hole in the orifice will determine how much gas flows into the burner and how hot the barbecue grill can become.
In the image showing above the far left hood orifice shows a starter hole which is how a orifice comes when it is brand new. The center image shows the hole in the orifice drilled for 25,000 BTU gas grill. Most barbecues have a burner rating of 11,000 to 13,000 BTU but these orifices were taken from a barbecue that uses a “U” burner which is like having 2 straight pipe burners. The far right image is an orifice made for natural gas. Notice the opening in the natural gas orifice is twice the size of the LP orifice.
The spud-style orifice showing in this image screws IN to the control valve instead of ON to the control valve like the hood-style orifices showing above. Different manufacturers will use different sizes and styles or spud orifices. Either type of orifice works the same way. All the orifices in this image are new and have starter holes in them. The starter hole, if used would allow approximately 7,ooo BTU of LP gas and if installed in a NG grill no gas would pass through this hole.
The two orifices showing on the left side of this image are both used in different versions of the Turbo STS model gas barbecues. On our site where these Turbo bbq grill repair parts are available the far left orifice is item 31500 and the smaller orifice to the right of the far left orifice is item 31300. The smaller spud orifice is approximately 5 mm at the hex head and the 31500 is 9 mm.
Some gas barbecues will have different orifices in the control valves and other orifices in the rotisserie, side burner or smoker burner so always check to be sure of what is needed. An orifice is basically like the jet in an old carburetor. The gas flow is affected by the opening in the orifice.
As an example this is a picture of a Viking control valve with a hood orifice on it. If this was in a natural gas barbecue and the barbeque needed to be converted to use LP gas this orifice just unscrews and the new one screws onto the control valve. The orifices are not usually visible in the bbq. Remove the cooking grates, the heat plates and lift the burners out of the barbecue. In the front fire wall inside the cooking area is the hole where the venturi tube of the bbq burner goes into the control panel. Using a 7/16 inch ratchet socket the orifice can be unscrewed and the new orifice screwed onto the valve.
Majestic Grill Parts
4 Feburary 2012.