BBQ Grill Control Valve Orifice Air Shutter and Burner Assemblies.

by grillrepair on January 4, 2013

grill schematic of control valve to orifice to burner and air shutter

schematic drawing shows the assembly of control valve, orifice, burner and air shutter carburetor.

 

We get a lot of calls from clients asking about control valves or orifices or air shutter adjustment and how these parts affect the performance of the burner and the overall barbecue.  This drawing shows the basic set up that is pretty much the same in all BBQ grills.

The control valve is the part of the grill that has the control knob attached to the valve stem and allows us to control the gas flow to the burner.  The valve stem is usually a round metal post that has a cut to make it flat on one side.  The shape is referred to as a “D” because the circumference of a valve stem looks like the capital letter “D”.  The opening in the control knob should be the exact opposite shape and look like a cut-out of a capital letter “D”.  Some valve stems are solid and others are hollow inside and some valve stems are slit down the center.  The hollow valve stem will usually have a set screw down inside the stem to adjust the movement of the control knob.  The split valve stem allows us to squeeze or spread the pieces of the stem to adjust knob tightness.

On the tip of the valve opposite the valve stem and facing the burner is threaded for attachment of the orifice.  This is like the jets in a vehicle carburetor that only allow a specified amount of gas to pass through the opening.  The valve will either have threading on the outside of the tip so a “hood” orifice can screw onto the valve or the valve will have threading inside the valve tip to accept a “spud” style orifice.

hood style orifices with lp and ng openings

Hood orifices with LP and NG holes drilled for various BTU settings.

Notice the holes in these 3 hood orifices.  A control valve that has threading at the tip opposite the valve stem is threaded so the hood orifice can screw onto the valve.   The hole in the orifice determines the maximum amount of gas that can pass through into the burner.  Oddly enough of the orifices in this image the 2 orifices on the right side are drilled to  allow 12,900 BTU.  Obviously the hole in the orifices are very different with the left most hood orifice showing a tiny hole and the middle orifice hole big enough to see through.  This is because of the difference in the mass of propane and natural gas.

LP stands for liquid propane and propane cylinders are filled with liquid.  Propane was a very low boiling point — that would be freezing for us — so the liquid boils or vaporizes along the inner lining of the LP cylinder.  The liquid turned into gas has a very small mass so a lot of gas can flow through a very small hole.

Natural Gas has  a mass that is more than double the mass of vaporized LP so the same amount of fuel needs a much larger hole to flow through.

When someone does not convert a barbecue grill properly when converting the appliance for NG to LP or LP to NG often the orifices are the problem.  Run LP through NG orifices and the flames emitted from the burner will be Huge.  Run NG through an LP orifice and the flames will be tiny — if any NG gets through at all.

brass cobversion spud style orifices

These orifices are “spud” type orifices that screw into the body of the control valve. The hole in the tip determines the maximum flow of gas.

This second image is “Spud” style orifices.  Although the hood orifices attach by screwing over the tip of the barbecue control valve the spud orifices screw into the body of the valve.  The valve manufacturer will make most valves able to use either a spud or a hood orifice depending on the type of venturi tube and air shutter on the burner and depending on the length of the control valve.  Very rarely does a control valve have threading on the inner and outer tip of the valve.  A valve will require either a hood orifice or a spud orifice.

The middle of any control valve has an attachment to the primary gas line. In a gas grill this is called the manifold just like the similar part in a car engine.  The manifold is a hard pipe that is attached to the gas flow hose coming into the barbecue.  The manifold will have one or many control valves attached to the pipe to draw gas from the manifold.  Depending on the amount the valve is opened and the size of the orifice opening the valve will pull some amount of gas from the manifold to be sprayed into the grill burner.

Where the orifice sprays the gas into the burner is called the venturi tube of the burner.  Most venturi tubes have an adjustable shutter so air can be sucked into the venturi tube as the gas sprays into the burner.  Depending on the gas pressure, BTU setting and the length of the orifice or the tip of the control the air shutter will be opened or closed to allow gas to mix with air which is what makes gas flammable.  A gas flame should be about 1″ to 1.5″ long and should be blue with a white/yellow tip.  If the flame is too yellow the air shutter probably needs to be opened more.  If the flame is noisy and appears to be floating off the burner the air shutter should be adjusted for less air flow.  The air shutter has to be adjusted while the burners are burning and the air shutters are visible which usually means removing the control panel of the barbecue grill and then lighting the burners one at a time.  Once the air shutter has been properly adjusted tighten the set-screw on the air shutter so the adjustment does not change.

Even when people make adjustments to their orifice or to their valve or their regulator to get more heat out of a barbecue the air shutter should be readjusted to ensure the gas flow is proper.  For instance someone who re-drills their orifice for more gas flow will usually also need to adjust the air shutter.  Leaving the air shutter incorrectly adjusted usually means food will be affected by fumes, gas by-products and smoke or soot which can be very unhealthy.

kalamazoo control valves and manifold and orifice with gas hose copper

These Kalamazoo valves have an extension between the valve and the orifice.

The orifice has to be inserted into the burner venturi and the edge of the front tip of the orifice should extend into the area of the air shutter.  The orifice should not just barely be inserted into the burner because splashing can occur.  Typically the edge of the burner will be .25″ from the edge of the side hole for air flow.  The orifice in this instance should enter into the burner at least .5″ because that allows for 1/4″ of the orifice extended in between the air shutter holes.  This way the gas flows into the burner and pulls air in with the gas but the gas is not being sprayed from so far back that it flows out through the air holes.

Some very few barbecue grill models used a slightly different design.  The control valve has a flared gas line or a compression fitting with a copper or aluminum gas line attached.  This way the orifice can be inserted into the burner in a different location than where the gas valves mount to the manifold.  These extension orifices are usually indicative of a poor design to the barbeque because the manufacturer did not ensure the valves attached the the manifold at the right location to be inserted into the burner and the burners are the right size to be installed next to one another.

Finally the burner.  The burner is the last place for the gas to go and the burner has almost no determination at all regarding heat output.  If we remove a pipe-burner and install a U burner there is usually no difference in the flames at all.  The burner does not determine BTU or heat in the grill.  The only time a burner can become problematic is if a lot of the ports (holes for flames) are clogged or if a large burner with a lot of space and a lot of ports is replaced by a much smaller burner with a lot less ports.  We have done this many times without experiencing “flash-back” but it is possible for more gas to flow into the burner than can be emitted through the burners ports.  This would result in gas getting backed-up and flowing back out through the venturi tube which is extraordinarily rare.

Any time a customer has contacted us to say the burner has flames coming out of the venturi tube the problem has been a user error or a cleaning problem.  Usually the burner is slightly crooked and the gas is spraying into the burner venturi tube and hitting the walls of the burner so the gas leaks out through the air vents or venturi tube.  A very dirty grill could also do this but this is rare because the unclogged ports will usually transfer enough heat to clean out the ports near the flames.

Got questions about repairing your barbecue grill, replacing any grill parts or adjusting your burner control valve or an orifice, burner, air shutter, etc?

Contact Majestic Grill Parts Anytime!

954.247.4552 (954-2-GRILL-2)

Service@Grill-Repair.com

 

 

 

 

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