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Hiccups in an LP forge


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So I built a forge a week or so ago, and the first day I really got it fired up, the burner started hiccuping. I was thinking it was due to too much air, but I didnt want to crank up my gas in the mix, so I came online and looked around some. I found a post on another forum that said it was an issue of too little air in the mix, and to turn the gas down once the forge heats up all the way. I just tried this theory and what happened was vastly more hiccuping with the gas mix down. I turned it back up and the hiccuping subsided mostly, but not entirely.

 

Any thoughts? At first I was afraid I have an unknown leak somewhere, but I don't think that's whats going on. Is this a common occurrence?

 

I just want to make sure my forge is safe to run for extended periods of time.

 

Thanks!

 

Justin

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"Hiccuping" as in instead of PHHHSSSSSSHSHSHSHHSHSHSHHSH it's PSHT PSHT PSHT PSHT? It happens to me whenever my gas tank gets too low on gas.

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Haha, yeah. But the tank is more than half full. I have a gauge on it to track my consumption. :/

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You can check for leaks with soapy water. Use a sprayer bottle, if you don't have a place to buy one throughly rinse out a windex bottle or such. Spray the mix on any connection where you think you may have a leak, if it bubbles you have a leak. You should periodically check all connections for leaks, as they do get bumped and sometimes it happens. Usually once they have been leak checked they are OK but like I said it doesn't hurt to recheck once in a while just to be on the safe side.

Hicupping can be an indication of a pressure problem.

Are you using a high pressure regulator?

 

Are you using the small 20lb tanks as a source for your propane?

 

Have you checked to see if your tank/s are low?

 

Freeze up can cause pressure problems!

Freeze up usually happens when using only one 20# propane tank at a time. The forge is drawing so much gas out of the tank at a rate that the tank will begin to freeze up, and that in itself will cause the pressure problems. That can be remedied by manifolding two tanks together so that the propane is being drawn from both. This will usually stop the tanks from freezing! Here is a pic of my tanks I use with my forge. I built this carrier so when not in use I can wheel them around with a dolly and store them away from my shop where there are sparks that might ignite an accidental leak!

 

Forgecarrier004.jpg

 

Usually anytime their is a problem with the burner it is either too much air or gas or not enough gas. The flame should burn blue, yellow indicates, more than likely too much air and not enough gas.

 

Hicupping in my experience is usually a pressure problem!

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Thanks a ton!! I'll work on getting a second tank set up and linked in to try and prevent this.

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You haven't said what kind of burner you're using, I'm assuming a venturi? On a blown system a "pop, pop, pop" is a symptom of a lean fuel/air mix, so it should be the same on a venturi. I'd guess that that the regulator isn't providing enough pressure. A BBQ regulator really isn't enough, you need a variable pressure regulator, like these.

 

Geoff

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I believe you posted earlier that you built the Venturi burner from my plans. http://www.bladesmithsforum.com/index.php?showtopic=26862

Assuming that is the case, you have one of two problems:

Both are possible, but based on your description of the "hiccup" and the fact that turning up the gas helped, I am betting your immediate issue is #2.

 

1. As already mentioned, your gas line may not be supplying enough gas.

This can be due to small tank freeze-up or due to an inadequate pressure regulator. I would recommend nothing smaller than a 100lb tank, but you can basically expect about 30 min per 20lbs before you start to get significant slow down in gas flow. Once you get above 100lbs the tank will be able to maintain a good enough heat exchange with the environment to keep up in all but the coldest weather.

For regulators, keep in mind that the typical BBQ grill regulator gives a fixed 11" water column (roughly 0.5 psi) which is pretty much the lower limit for a Venturi to maintain in a pre-heated forge. When first lighting up I would aim for ~3-4psi at the lowest. If you end up buying a new regulator, try to find one with an upper adjustment range at least double the highest pressure at which you plan to operate (I use a 1 - 60 psi regulator on a 120 gal tank). Most non-industrial LPG regulators expect the high pressure line to feed distant or multi-branched low pressure lines so the max flow rates tend to be relatively low the closer you get to the upper end of their pressure ranges, which makes the forge behave like the tank is freezing-up.

 

2. Other option is that you have a cross draft at the forge that is disrupting the back pressure in the forge chamber and making the burner act like it is running lean. Once the forge hits a good heat it tends to even that out, but while it is heating up you can give it extra gas like you mentioned in your post, or leave the gas alone and manage the cross draft until your forge heats up. This can be as simple as placing a fire brick over the opening on one side of the forge so the draft can't flow straight through.

Unless you have a fan pointed directly at the forge, the "hiccups" should settle down once the forge gets up to fairly even forging temperatures.

 

Hope one of these takes care of your hiccups!

James

Edited by James Spurgeon
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this is a common problem in tuning venturi burners, I have found it is in most cases a matter of to much or not enough back pressure.

I have solved it with a number of methods.

first a good flared burner tip this helps balance the flame in the right place. if the flare is meter they do wear out even stainless , I cast mine in refractory then build it into the forge body done this way I haven't burned one out yet. depending on the forge design, next would be the tip of the burner tube getting to hot , move the burner back 1/2 or so and see if that fixes it. to much back pressure this is mostly a factor of burner design but a choke can help in balancing the flame or reducing the back pressure by filing the tube smooth shortening it slightly or changing the angle of the burner in the forge, however oddly to little back pressure will act the same though generally isn't and issue when installed in a forge as the forge will provide enough back pressure . the last adjustment that can work is adjusting the angle and position of the gas jet in the air inlet moving slightly off straight can fix the issue sometimes as can moving the jet almost into the mixing tube this changes the mix some but also changes the velocity of the air being pulled into the mixing tube adjusting the needed amount of back pressure. a real good book on this any one I still reference is http://books.google.com/books/about/Gas_Burners_for_Forges_Furnaces_and_Kiln.html?id=nHkpb4cCKvQC

MP

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