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Harry Marinakis

Blown air forge propane plumbing question

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I'm building a blown-air ribbon burner forge with a needle valve for fine flow control of the propane.

 

1. If I am using a needle valve, do I need a pin-hole orifice downstream from the needle valve to help regulate propane flow?

I'm guessing the needle valve alone is sufficient.

 

2. Where should I put the 0-20 psi pressure gauge? Before the needle valve, or downstream from the needle valve?

I'm guessing between the high-pressure propane valve (that's attached to the tank) and the needle valve. 

Edited by Harry Marinakis

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Check out the Build a Gas Forge and the Ribbon Burner attachments on the Forge Supplies page at www.WayneCoeArtistBlacksmith.com.

Let me know if I can help you.

 One of the attachments shows how I plumbed my Ribbon Burner forge.  I have the regulator/pressure gage at the tank.  I have no orifice and the needle valve is at the air supply pipe.

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Good info on Wayne’s site. Make sure to have a read. I have a lower reading pressure gauge right at the burner (which would be after the needle valve) so I can see what my output pressure is. This is to allow me to have some guide to setting the forge for certain temperatures. At the moment it goes up to 10 bar but I’m going to replace it with a lower rated one as it doesn’t allow for fine tuning.

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I have made a lot of progress on making my blown ribbon-burner forge, but I have another question.

 

I made the stand and the body of the forge (see 1st photo). There will be 3-inches of ceramic blanket insulation all the way around. The forge is open on both ends (small opening on the far end). There is a stock support bar that telescopes in and out to suit the length of my stock.

 

I have a rough propane plumbing plan (see 2nd photo).

 

The blower is on a rheostat, and can provide up to 135 cfm. The blower will be attached to the open end of the 2-inch pipe. There is a static mixer in the cross piece.

 

The propane screws into the end of the brass pipe. Continuing downstream, there is a pressure gauge  and a needle valve. Downstream from the needle valve, the propane flows through a 1/4-inch pipe directly into the 2-inch steel pipe.

 

Both the rheostat and the needle valve will be mounted on a control panel on the right front leg of the stand, so that both are within easy reach when I'm at the front of the forge (see 3rd photo).

 

PROBLEM & QUESTION:

 

I reviewed this forge with an engineer who also built a ribbon burner forge. He says that they are many flaws my design, including:

 

1. There is too much 2-inch steel pipe between the propane input and the ribbon burner head . If the blower went out, the flame could track back into the pipe and cause an explosion. He said that the propane should insert into the 2-inch steel pipe just a couple of inches away from the ribbon  burner head.

 

2.  There should be a welding tip nipple downstream of the needle valve, where the propane inserts into the 2-inch steel pipe, to provide a restricted jet of propane into the steel pipe.

 

Comments, please?

 

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Edited by Harry Marinakis

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There is absolutely no need for the welding mig tip. And propane will not burn without oxygen so there is no risk of explosion or the flame back tracking into the pipe. 

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I use a oil forge and gasoline for preheat and thinning. It doesn't pose an explosion hazard with any size chamber (3" pipe to 16"tank) at most a moderate to annoying blowback that'll ruin your fan and give you a 2month surprised look before exploding. It takes quite a bit to burst a pipe like that. It'll never happen with standard fuel. 

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Propane is heavier than air so you want the blower above the burner head otherwise propane can settle into the fan and cause a small ignition when the fan is powered on. I personally start the fan before feeding propane to prevent this from happening.

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Better to use Kerosene rather than Gasoline.

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Absolutely no MIG tip needed on a blown burner.  Geoff Keyes once blew up a fan, though. There is merit to having the fan high rather than low, but I know lots of guys with the fan low who have never blown one up.  Your call.

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My blower, before it was stolen, sat lower than my forge and the gas injector and I never had an ignition in the blower the next time I used it.  I think the reason is that I always turned off the gas before turning off the blower so that the air line was purged of any gas before I turned the blower off.

 

Doug

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@Wayne Coe I just came into 5gal of methanol to see if itll give me a more "gently" startup but honestly gasoline gives me that much needed oomph and instant heat. The worse ive experienced, my fault, was using a large volume burn chamber that loved getting the right mix to often and blowback destroyed 3 fans before i realized a 3" pipe works just fine and has no blowblack. Less volume is much safer with probably any fuel in a premix environment. From my experience with far more volatile and inherently dangerous forge setups i see no reason his would be a hazard. even in the event of blowback, a fan that strong would certainly create a vapor wall the fire couldnt push aside. Worse case youll mess up your cast ribbon burner

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My blower is lower than the gas inlet.  I always turn the fan on first then fuel for start up.  I always turn the gas off first then the fan. 

 

4 hours ago, Doug Lester said:

I never had an ignition in the blower the next time I used it.

Any vapor would have dissipated before the next use.

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I've run blown forges, glass furnaces and glory holes for many years.  In all cases the blower was below the gas inlet and I've never had a problem in the blower either.  The key, as others have stated is the sequence for lighting and turning off your forge.  That being said there are a few other things I agree with:

  1. No small orifice is required for your burner construction.  However I would substitute a proper propane regulator with gauge and a 1/4 turn gas rated ball valve for the proposed needle valve.  In my experience needle valves are not reliable long term and it is nice to have a quick shut off in case of any issues (like power going off to your blower for whatever reason).  That being said, a 1/8" -1/4" pipe connection to the burner mixer is a bit more common for propane.  Your's looks like at least 3/8"?
  2. You need bubble tight joints on your fittings.  This is easier to accomplish with the correct gas rated pipe thread compound.
  3. The allowable length of pipe between the blower and burner outlet is more a function of the blower capacity than any worries about burn-back.  The only times I've seen people having trouble with preignition is when they let the mixer assembly get too hot.  This is more often a problem when you are trying to run your forge at  a lower temperature after it has been very hot, or light it when a chimney effect has come into play.  In my experience this is less of a problem with multi-outlet burners (like your ribbon burner)
  4. That looks like a rather large forge for a first forge.  What is your planned interior volume?  Beware of gas hogs and try to plan for doors early...

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I also have my blowers below the gas inlet. I used to have it above but got annoyed with the heat chimney-ing up into the fan after it was shut down so I moved it below. That said, I turn on the fan before I even hook up the gas line. I have a quick disconnect on the tank side of the line (which hooks up to a 500 gallon outside the shop). So it’s easy for me to turn on the fan then run go hook up to the gas.

 

I will also add that I agree with Dan on pretty much everything he said. But, I wouldn’t want to get rid of my needle valve. It gives you a lot of adjustability for your gas when fine tuning atmosphere or heat. However, I also have a 90 degree ball valve directly behind it for a quick gas shutoff if needed.

 

Dan hit the nail on the head though. My first forge I built was an enormous gas hog and, while it was the right size for my Damascus, it was really too big for just forging a hunting knife. I have since swapped my main blade forge to a much smaller forge and only heat up the big one if I’m doing Damascus or something big. I wouldn’t make it any bigger than you think you need for what you plan to forge. But, you can always make more forges :)

Edited by Cody Killgore

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Thanks for all the input. 

 

This is not my first forge. I have a 2-burner NC Tool forge that I bought second-hand. It has been very unsatisfactory and too small. It won't get to welding temp and is a gas hog.

 

The interior dimensions of my new forge:

Length 14"

diameter 5" 

That's 275 cubic inches. 

 

I am planning to leave the plumbing alone, except I will run 1/8" tubing from the needle valve to the 2-inch pipe.

 

I am also making a tiny table-top forge for making tools like punches. 

Edited by Harry Marinakis

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Depending on the length of tubing t may be worth upping the size of your propane supply to 1/4".  You need to be prepared for friction loss at a certain point.  It is kind of a mixed bag.  On one side you have a restriction that could limit your overall propane (and thus heat) supply, on the other a smaller orifice at the mixing point will speed the entry of propane into the mixing tube, aiding in mixing.  The compromise I've made in the past is to run a larger tube to the mixing chamber, then cap same inside the chamber with a drilled orifice.  See this site for a typical example:  https://www.joppaglass.com/burner/rt_alf.html .  For a forge a multiport outlet isn't required (though they are nice, and a good choice for a long thin forge), and you can vary which arm of the TEE the air and gas enter on depending on your blower characteristics and fuel source pressure.  I reiterate that I prefer variable pressure regulators over needle valves, but if you are set on the latter, be sure your's is rated for gas service.

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Dan,

I'm not following your last post. 

1/4" propane supply tubing -- you mean where the propane connects (3/8" right now), or the tubing from the needle valve to the 2-inch pipe (1/4" right now, but am considering 1/8").

 

Variable pressure regulator versus needle valve. I have such a reg on the propane tank, that's all you use to regulate flow? I have a quality precision needle valve. 

Edited by Harry Marinakis

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A regulator controls pressure, a needle valve controls volume, two different things. With a Ribbon Burner you want to be able to adjust the air/fuel mixture just like with an oxy/fuel torch.  With an oxy/fuel torch you have regulators at the tanks and valves at the torch.  You want the same thing with a Ribbon Burner.

Edited by Wayne Coe

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Thanks Wayne. Wouldn't a regulator on the propane tank and needle valve downstream from the regulator do just that?

 

Or are you saying that I need a regulator on the propane tank, and another regulator downstream from that?

 

Edited by Harry Marinakis

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A regulator on the tank to regulate the pressure and a needle valve on the line to regulate the volume.  I would also put a 90° ball valve on the line for an emergency shut off.  Just a quarter of a  turn and you've shut everything down without having to adjust the other two.

 

Doug

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8 hours ago, Doug Lester said:

A regulator on the tank to regulate the pressure and a needle valve on the line to regulate the volume.  I would also put a 90° ball valve on the line for an emergency shut off.  Just a quarter of a  turn and you've shut everything down without having to adjust the other two.

 

Doug

Harry, look at the picture of my forge and read the attachments on the Forge Supplies page of www.WayneCoeArtistBlacksmith.com. follow Doug's comment.

 

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I've never needed a needle valve to regulate the flow in my builds.  A good regulator can very precisely adjust the pressure within 1/2 psi.  For a given fixed geometry gas train piping system the pressure of the gas at the source directly dictates the flowrate (unless some kind of compressor is added, reference the extended Bernoulli's equation).  A good needle valve changes the piping system dynamics by adding a local restriction to the flow and allowing you to reduce the flowrate without adjusting the main system pressure at the regulator (if you initially set the regulator to run very rich at full air flowrate you can use the needle valve for more modulation, both up and down, but you need to plan that in advance).  The same thing can be accomplished by adjusting the regulator, but you can also increase the flowrate using the regulator.  It is my opinion that one point of control for the gas is better than two, but each to his own.  A needle valve would certainly make it easier if your propane tank and regulator were located outside your shop.  It will allow gas flow adjustment while viewing the results in the forge.

 

I believe that the use of needle valves in DIY burners dates back to the time when folks on shoestring budgets did not wish to purchase quality propane regulators.  Needle valves used to be cheaper and more common.  The popular RISD glass furnace/ceramic kiln burners from the late 60's (I think) are a good example of this.  The valves on torches are extremely useful because they are localized to where you are working, and the typical regulators are less precise.

 

These days I use a commercial burner/mixer system for forced air/natural gas on my personal forge.  It has a sophisticated zero pressure regulator which allows you to set the desired gas/air proportion (within a general range), then adjust the volume flowrate of the gas air mixture with a single control (similar to the upgraded shower controls where you set the temperature on one dial and the flowrate on another).  It works very well, but I probably wouldn't use it if I hadn't gotten it for free while dumpster diving after a local university completely relocated their glass studio and threw away all the original piping.

 

15 hours ago, Harry Marinakis said:

1/4" propane supply tubing -- you mean where the propane connects (3/8" right now), or the tubing from the needle valve to the 2-inch pipe (1/4" right now, but am considering 1/8").

 

 I would leave it at 1/4" and only change it if you have trouble with either mixing or controlling flowrate down to the minimum desired (watch out for preignition at low flow...)

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Lots of great info here, that will be useful to others as well. Thank you again. 

 

I keep my propane tank and regulator away from the forge, so my plan was to mount a needle valve next to the blower rheostat at the control panel at the front of the forge, where I can fine tune gas and air flow while standing in front of the forge. Having never made anything like this before, I wasn't sure that it would work. I will add a 1/4-turn shutoff to the control panel. 

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