gas igniting prematurely(burning in venturi)

[Jim S]

I have a forgemaster two burner gas forge.  Usually when it initially starts, it gurgles for a few seconds due to, I guess, premature ignition.  Several days ago the gurgling didn't go away and since I only wanted to heat a small piece of steel to anneal it, I left the steel in place for a few minutes.  However when the powder coat began crinkling (burning/melting(, I shut everything down.

 

Factory literature says one of the burners is igniting prematurely.  However,  there is no mention of what to do.  An email to Forgemaster has produced no response to date.  Does anyone have any suggestions for correcting the problem?

Thanks.

Jim

[Dave Hammer]

I don't know about that particular forge, but it's likely that there is an obstruction in the burner (probably the orifice).  I'm assuming that one of the burners is working properly.   You should be able to recognize that by looking into the forge.  If there is a shutoff valve near the burner(s), crank up the pressure as high as you can, then turn the shutoff valve off, then on right away.  If that doesn't work, disassemble the burner(s) and use a welding tip cleaner to clear the orifices. 

 

If that doesn't work,  you probably need to disassemble the manifold to see if there is junk in there anywhere.  Blow it all out with high air pressure (careful not to damage your lining).   I have had "what looks like wax" build up in plumbing.  One more thing, mud daubers love to crawl into small places and do their magic.  When they do, it usually just takes a thorough cleaning and things start working again.

[Jack Evers]

I don't have a Forgemaster. but this time of year is when I have trouble with plugging orifices Don't know why, but  follow Dave's advice.

[ciladog]

Forgmaster forges do not have a venturi;  they are aspirated forges.  Now that may be splitting hairs but understanding how the forge works will help you fix the problem.

 

A venturi (the venturi effect) is a restriction  placed in a tube that speeds up the flow of fluid (air) in the resturced area creating a low pressure area (creates suction) simply put.  Aspiration is to draw something in by suction.  Like I said, splitting hairs. 

 

The gas flow in an aspirated forge is forced through a small orifice to create a thin, high pressure stream of gas.  As that stream of gas flows into the manifold it creates a low pressure area around it and  pulls air in behind it.  The gas and air mix as they move through the manifold.  So with all that being said, if you have ignition in the manifold you do not have enough high pressure gas flow in the manifold.  You can hear a drastic change in sound when the gas burns in the manifold.  It sounds like a ramjet engine.  Always shut it down when that happens and restart the forge.

 

Take Dave's advice and break down the burner and make sure you have no obstructions.  Then increase your gas pressure.  On a two or more burner forge it is a good idea to place needle valves on the supply lines of each burner so you can balance out the gas flow.

 

For those of you that want to take this further check out Bernoulli's principle.  It is how carboration in cars has worked for most of their history, that is until fuel injection.

 

And did you know that it is also how airplains fly?  Really cool stuf if you are into physics.  The wing of an airplain called an air foil is longer on the top than on the bottom.  And yet two molicules of air hit the leading edge at the same time will  hit the trailing edge at the same time.  So the air flowing over the top of the wing has to move faster than the air flowing over the bottom of the wing.  This creates a low pressure area on the top of the wing and creates lift. 

Edited January 11, 2013 by ciladog

[Jim S]

Thank you all. I will implement your suggestions.
Jim

[pkrankow]

If you don't have torch tip files (tiny wire files, usually in a set) get a set before opening this up. You may have trash or damage to the tip of the orifice. A little tip file can clean any trash inside the orifice out and make life nice.

I had an interesting curl of flame inside the burner when I built my forge burners. A sharp edge is needed so the fuel gasses part from the nozzle and continue in the desired direction.

Phil