Got a problem for Timmie (SE)

Johnboy

Steve, I am familiar with this furnace. e-mail me and we can discuss it.

Steve Ebels_3

Problem for Timmie(SE)

I know this was a discussion topic a while back but I can't find it in the archives.
My boys went to check out a gas leak last week and while there the HO said "can you take a look at this one burner, it lights back in the tube once in a while".
So after finding the leak they checked gas pressure, (LP) right at 11"w.c. where the spec on the furnace called for. Andy tried opening the air shutter on the burner tube first, then closing it. Very small increments each time between checking for a good light off. About every third or fourth time the flame will start on top of the burner and then pop back into the tube.
The burners are all new, the orifices are all correct. The furnace is a 90% eff Dayton brand (Heil) about 12-15 years old. It's the one that the inducer lays horizontally at the bottom of the burner compartment. The Dayton model may be 3E465 but it was fairly well obliterated.

What makes these cussed things pop back like that. Too much or not enough air? Andy said it lit better with more rather than less but the flame acted like it was getting too much air when dialed in for a halfway decent lightoff.

pitman9

We've had similar problems with some LP Utica boilers

They had us check quite a few things including changing the burners (a Michigan burner they called it). Other possible causes were:

Loose pilot nut - this one has happened twice. They use a sealant on the nuts when they make an LP unit at the factory but it's not included in the LP conversion kits.

Orifice tapping not straight into the burner - put a nipple in the orifice hole and make sure it's not pointing toward the side of the burner.

Make sure the burner orifice is the correct one.

It can also be an LP quality issue. Apparently they have a lot of problems with the LP in Michigan. Hence the "Michigan" burners.

Steve Ebels_3

Problems with LP

You can say that again. Seems like every manufacturer has some different "solution" to LP ignition problems. The Bryant/Carrier dealers around here are replacing HX's by the truckload and Carrier keeps blaming it on gas and pressure issues. Their LP kits now include a pressure switch that won't allow the furnace to ignite unless gas pressure is within their allowable tolerance.

Based on all the problems I see with it, I wouldn't use LP for heating fuel unless it was the last option on earth. It's crazy though, some folks seem to never encounter problems with their equipment while the person next door, often with the same stuff, has mountains of grief with their furnace or boiler.

Ed_26

LP burner

Try reducing gas pressure - 10.5", 10" etc. What is the elevation (in relation to sea level)? Has the gas valve been changed?

Steve Ebels_3

Our elevation

Is around 1,100 ft above sea level. Never had to adjust orifice size for that. When I get back to the place I'll try the gas pressure and see what happens. Thanks

GW

best of luck

We had a new Smith GB200 (gosh, is that right? I'm getting foggy on my smith model numbers) a couple of years ago do that. Drove me nuts- it would only happen once every few weeks. I actually don't think I ever saw it happen; the home owner informed me and I had no reason to not beleive him.

I checked pressure, combustion, the basics. Had the Smith guy out. Twice. We slapped in a step opening valve and haven't heard back; this was late winter this past heating season.

Gary

GW

best of luck

We had a new Smith GB200 (gosh, is that right? I'm getting foggy on my smith model numbers) a couple of years ago do that. Drove me nuts- it would only happen once every few weeks. I actually don't think I ever saw it happen; the home owner informed me and I had no reason to not beleive him.

I checked pressure, combustion, the basics. Had the Smith guy out. Twice. Second time we slapped in a step opening valve and haven't heard back; this was late winter this past heating season.

Gary

don_149

Sounds

Like to me a lazy flame do to one of your section on the hx
is clogged with soot.

Most likely the one that you're having problems with.Have seen it alot when customer run out of fuel.

Unknown

12 to 15 years old????

Has it been doing this all along or is this just something new occuring? Many times when burners get old and start to wear out they will "flashback" especially on LP gas. It is because the port loading on the burner changes. When this happens air adjustments may not help. It will only be cured by replacing the burners.

Make sure the input is exactly what it should be. With LP you typically do not have a meter to clock the burner so you will have to check gas pressure and the orifice size should be checked with a drill index to determine size then chart it out to find what the input is. it is critical that the input be right on.

Are the burners tube or gun style burners? If tube type are there slots cut into the burner itself. How many burners are there and are all of them doing this?

I will post a second post explaining "flashback" for those that are interested. There are several cause of "flashback" by the way.

Unknown

FLASHBACK

Our discussion centered around the problem of FLASHBACK. What is flashback? Under some conditions, gas-air flow velocity is less than burning speed at some point or points near a burner port. When this takes place the flame tends to strike back through the port to ignite the mixture in the burner head. This condition is known as FLASHBACK.

As noted in earlier discussions, the inner cone of a BLUE FLAME BURNER the flame visibly defines those points where flow velocities and burning speeds are balanced above the port. In a sense, flashback is a condition which the inner cone is inverted. It extends into the port, rather than above it, and ignites the mixture in the burner. A flow velocity-burning speed pattern would show flame velocity flashing back into the port with flow velocity trying to stay above the port.

With a properly designed and adjusted burner, flashback will not occur during normal burner operation. Under some other conditions it may happen. Any fuel gas property which increases burning speed tends to promote flashback. Any burner operating or design factors which act to decrease flow velocities from the ports also make flashback more likely.

Flashback tendencies are greater with faster burning fuel gases. Natural gas is a fairly slow burning gas, so is less likley to flashback than faster burning gases, such as the old coke oven manufactured gas of the past. increasing primary air increases burning speed thus increases the tendency for flashback.

Sometimes a burner may be underrated (undergassed), due to incorrect orifice size or low gas pressure, or both. Flow velocities from ports will be lower than normal, promoting flashback. A leaking burner valve which lets a small amount of gas flow to the burner can also cause flashback. Glenn Harrison brought up a point about a particular valve which was giving indications of gas leakage and requiring a change of valves only to see the problem present itself again. I followed up on this with the manufacturer and was told this problem was occuring due to impurites in the gas causing poor shut down on valve seats. They recommended that in all cases a sediment trap should be installed ahead of gas valves. GAMA (Gas Appliance Manufactuers Association) recommends that a sediment trap be installed ahead of all gas valves. I am not sure if this is what caused this problem but that is the answer I received. As a note the permeability values for gases through rubber diaphragms is extemely small (approximately 0.56 cc/hr (cubic centimeters and is almost negligible when compared to the 200 cc/hr maximum allowed by ANSI) (American National Standards Institute) (ANSI allows 200 cc/hr for outer wall gas leakage and 235 cc/hr for gas valve leakage) this is not enough gas to be detected by smell, soap test or combustible gas indicator.

In multiple burner appliances flashback may occur in one underrated burner. the overall appliance rate can still be close to its rated input despite one underrated burner. The orifices need to be checked at each burner, especially on brand new equipment which is when this is most likely to show up (poor quality conrol at the factory).

Smaller and deeper ports improve reistance to flashback because of quenching effects, reducing burner speed. This quenching action is lessened if the burner ports are hot. The quenching effect of very small ports or porous refractory material in RADIANT BURNERS prevents flashback, in spite of operation with a very high primary air and with a glowing surface.

Although flashback may occur in critical designs after the burners heat up, it is still possible for flashback to occur upon ignition of the burner. When a burner is first turned on, gas flow rate usually goes from zero to full rate in a very short time. The mixture in the burner head rapidly changes from all air to the steady-state mixture of gas and air. Flow from the burner ports goes from zero to that of normal operation. This period may be very short, lasting only a second or less. It is possible that at some instant the mixture flow from the ports will be low enough and burning speed high enough to cause flashback to take place at ignition. If full rate is reached quickly enough in this starting period, normal ignition should take place. The same is true if the mixture at igntion in that period is either too rich or too lean for flashback to occur.

Another type of flashback which occurs on extinction called EXTINCTION POP may take place when a burner is turned off. It may take place almost instantly or may be delayed by several seconds. This is what happens: More primary air flows into the burner, even though the gas jet is cut off and does not inject air. The mixture in the burner changes from normal operating mixture to all air. Flow rate through the ports falls of toward zero. Under these conditions it is possible for flame speed to exceed flow velocity at some instant and flashback may occur. The result is a tiny explosion or pop. Extinction pop usually presents no hazard but may be annoying to a householder. It may on occasions cause the pilot to be pulled out. It is most annoying on warm air furnaces with duct work acting to convey the POP sound into the livng area.

Bob Harper

Professor McElwain!

Timmie, you're the only guy I know who can take the Gas Engineer's Handbook and turn it into English! Bravo!

I like one chart in the Handbook that shows a graphic relationship btw flashback, yellow tipping, and lift off as a function of primary aeration and manifold pressure. As primary air goes up and/ or manifold pressure drops, the chance of flashback increases. Also, each gas has its own set of curves.

We have a patented process using ceramic fiber in a fireclay matrix. These burners are molded in something akin to a waffle iron, then drilled in a CNC router. The thicker cross section addresses those issues Timmie pointed out about port thickness/ diameter, extinction popping, lift off, etc. Makes quieter burners, too.

In the case with flashback, one test is to plug a few of the last burner ports in a run to increase port loading. Warning! Do not leave the equipment modified in this fashion! This is only a test to provide data to the Mfrs. Tech Svc. Dept.

There is one "flashback" Timmie failed to mention, probably because it is more common to hearth appliances: the Stealth Flashback. Instead of the flame speed exceeding gas velocity, this is a case where the air/fuel mixture migrates over to the ignition source from the venturi such as with a mis-aligned burner orifice/ mixer tube. Gas spills over or 'hops the fence' to ignite outside of the burner. Still, it presents with a roaring sound as the gas is burning right in the venturi. If you find a burner orifice spud all gunked up, you need to distinguish btw the two possibilities because they are totally separate problems and fixes.

Timmie, I believe those ANSI Z21.78 allowable valve leakages are at 3/4 psi aren't they?

You should always test a valve for proper closure of the main operator. You can do this two ways: starting with the unit totally off or burning, then open the TH circuit. You can measure for manifold pressure presence when there should be none. If you are anal like me, you can disconnect the burner supply tube and take your reading directly downstream from the valve. Then double check with a gas sniffer that can quantify as you will get some trace gas leakage. I've seen guys Poofed! from fugitive gas leaking into the combustion chamber before he calls for heat, then BANG!

BTW, when testing for leaks, don't forget the regulator vent. If it leaks steady you may have a ruptured diaphragm. It should burp upon initial flow of gas to equalize against the atmosphere.

Good stuff Timmie! Keep it coming!
Bob

Mark Hunt

Flash back


Thanks Timmie.

Two questions.

#1) How often does the lack of or an improperly sized sediment trap cause problems? Not just flash back, but other problems as well.

#2) I have been told by others in the industry that LP and Nat gas burners should have a slight amount of pitch to them. LP should pitch down since LP is dense and Nat should pitch up since it is less dense. Any comments on this?

Thanks again!

Mark H

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Mark Hunt

Good post Bob


Flammable gas will do some "interesting" things given the slightest chance.

I have on several occaissions had singed eye brows to prove it!

Mark H

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Steve Ebels_3

Timmie

The burners are new replacements from what the HO told my son. I don't know how long this has been occuring. The burners are a tubular slotted port design but not the laser cut newer style. They appear to be formed and then crimped over the material forming the slots.

Steve Ebels_3

My e-mail is

s_ebels@yahoo.com. Tell me what you know about this beastie Johnboy.

Unknown

The GAMA people

often talk about the need for a sediment trap as not all gas is as clean as we think it is. There can also be condensables in some gas which appears as moisture in the sediment trap. Without the trap all of this can get into the gas valve or controls and cause the valves to stick open. I have often taken gas valves apart and found all kind of strange stuff inside which is probably why the valve failed and was changed. Most of these on jobs that failed to install a sediment trap.

As for pitch on burners it depends on the type of burners. Most of the tube type burners which have a long way for gas to travel through the burner to reach the end should be pitched down slightly for LP and up for natural gas. I would not do that with cast iron port burners, gun burners or ribbon type burners. The boiler or furnace design should allow for proper setting and placement of the burners. I have over in my discussion area on Oiltechtalk a good description of all the different types of burners used on gas systems and how they should be set up. This is a vital part of proper burner setup before conducting combustion testing.

http://www.oiltechtalk.com/discuss/viewtopic.php?t=572

Bob Harper brought something up about blocking of part of the ports on the burners to test them. This is very important especially if the equipment has been converted from natural to LP. Many of the natural gas burners have to be replaced when converted to LP. The burners will flashback unless you get the burner designed for LP. The same style of burner on natural will have more slots than the LP burner. I ran into this recently on a Utica boiler I had converted and it would not stop flashing back. We taped of part of the slots and it fired fine. I then contacted Utica and requested a burner designed for LP. They responded with next day air and it has been fine ever since.

Something else that has come up recently is the Wobbe rating of natural gas as related to LNG and the possible increased BTU content of gas causing burners to be overgassed.I have written an article about this recently in HVAC Insider and I am working on an article contradicting the gas industry approach to this problem. It may be that gas which normally may have BTU content per cubic foot of 950 to 1050 may now be as high as 1300 BTU's per cubic foot. This will cause overheating and damage to heat exchangers and boiler sections along with increased carbon monoxide issues. It will definetly cause combustion problems and sooted up equipment. I am working on a possible procedure to follow to make adjustments to equipment that will prevent this.

Unknown

Steve I have a feeling

that these burners may not be designed properly for proper burning. I would ask for burners with reduced porting to replace them and see if this helps. If the problem did not exist before the burners were replaced and now it happens it defintely points to the new burners.

Many manufacturers are really laboring over poor burner design and application on a lot of there equipment.They send out new burners to replace fairly new burners that do not work. We never had these problems with all of the old cast iron burners. Where have all the old timers gone who understood burner design and proper burner adjustment. It is like many things a lost art to say the least.

Steve Ebels_3

Timmie

The burners are new stainless stell models supposedly designed for LP. I couldn't agree more on the design of slotted port burners. The only thing one can say about them is that as they are usually done by most US manufacturers, they are cheaper to build than the cast iron types.

It's interesting to note that I have never had any problem at all with that type of burner from Viessmann or Buderus on their atmospheric or draft induced equipment.

Bob Harper

club membership

Mark, I think we all have "Kissed the Dragon" at least once in our careers! Thanks for the kind remarks.

Timmie, we have seen a marked reduction in flashback with the advent of our firebrick proprietary burners. The thicker cross section combined with the ceramic material sure seems to keep the beast at bay. It also seems to make port loading less of a challenge.

I am very interested in the properties of the LNG and Wobbe numbers. Maybe this focus will also bring a little light on their practices of peak demand spiking with heavier hydrocarbons to meet the load. Of course, they never advertise when they are cheating us with propane, butane or what ever iso-N is on the shelf.

One other source of flashback that is difficult to diagnose so you must have a high index of suspicion is due to sudden significant drops in inlet pressure with high primary aeration. When you have a high BTU load house with small piping, there is always a chance you can get flashback when a Big Momma such as a pool heater kicks in and the inlet pressure to everybody else dips for a moment. I've seen it literally such the flame back in like a backwash effect. These monsters should be on a separate 2 psi system but the operative word there is "should". Others in the hard to prove category are LP regulator freeze-ups and firing of two major appliances simultaneously. You have to be there with a manometer connected to prove it. That's why we're getting our techs to check inlet pressures with just the pilot lit (we can still do this with an IPI system by simply disconnecting the green wire from the burner solenoid), burner 'on', and house full load test with our appliance included. We often find pressure drops like this: 6.35 static inlet pilot only; 5.52 burner on; 3.21 full load test. My appliances require a minimum of 5.0 inlet for NG. You wouldn't catch this unless you did the full test.

So Timmie, instead of clocking meters and calling PECO, who ain't known for sharing specs on their NG, is there any equipment/ technique for field use (that doesn't cost the price of a house) that could make a determination of sp. gr./ vapor density or Wobbe? I haven't been able to find a portable pocket sized gas chromatograph/ mass spectrometer for under a few hundred K$[grin]
hey, we can all dream. I'm still waiting for an oscilloscope and calibrator.... ain't holdin' my breath!

Instead of Wobbe, they should have called it "woe is me!"

Good thread!!
Bob

ricoallen77

burner flashback

I turn the furnace on and the pilot is lit, it takes a 8 second delay then lights up and flashback . When it do that , it blows out the pilot and nothing is lit.I cleaned the burner, could it be the gas valve ?

nicholas bonham-carter

New thread needed

Start a new thread for your question, so your post doesn't get lost in this one.--NBC

Tim McElwain

You are having a

delayed ignition not flashback. The burner should light in less than 4 seconds. Have a professional take a look at the equipment as a number of things can cause a delayed ignition.