Blown burners, the care and feeding

[Geoff Keyes]

I seem to answer this question once or twice a month, so I asked the powers that be to pin this for us. If I'm not clear, ask the question.

 

I like blown burners, they are brute force and dirt simple (just like me), so if you are looking for venturi advice, you must needs go elsewhere.

 

SAFETY WARNING

Building and operating a burner like the one described below is dangerous. It can burn you (since hot is what it does). It can create explosions of various sizes. You are responsible for your safety, the safety of your shop, and the safety of everyone around you. Properly built, properly used and properly maintained, they are safe to use. Use appropriate caution.

 

SAFETY WARNING

Further Safety Warnings

I don't put any teflon on the threads of the burner parts. The burner is not pressurized so it has never been a problem for me. If you find that you've got a leak, then I would seal that up. The gas connections should all be sealed and checked frequently. If you smell gas, shut down and find it. Propane is heavier than air and it can fill up a building, which can ignite and do a lot of damage. I have a big tank of propane (150 gallons) outside the shop. I always turn the gas off and let the gas in the manifold burn out when I am done forging. That way nothing is pressurized when I'm not around.

CO. These forges produce a lot of CO (Carbon Monoxide). Don't use them in an enclosed space without providing for an exhaust fan. If your work space is small and/or enclosed a CO monitor is prudent. I work in a big space, the hot shop is 2 stories and not particularly air tight, so I've forgotten about these kind of precautions. Thanks for reminding me.

This burner has been around in one form or another as long as I have been doing this (mid '80's). The only innovation on my part is the use of reducer bushings. The bushings mean that there is no fabrication to do, all of the parts are available off the shelf.

 

The burner is pretty basic. It's got two legs, one for the fan, one for the gas. As far as I can tell, the only critical part is the reducer at the injector end. Without a little bit of back pressure the flame is weak and hard to control.

 

I like to build the burner in either 1.250 or 1.50 pipe. 1" is too small, it's hard to get enough air through the system to get a good burn. I've never had a forge that seemed to need a 2" burner.

 

 

HEALTH WARNING

You can build the burner in galvanized pipe SO LONG AS the injector nipple and the reducer are black iron. If the galvanized pipe gets hot it lets off zinc smoke, which will make you sick. Zinc smoke has long term effects (see welders disease on the internet) and has been known to kill.

 

A basic parts list

 

1 Elbow

1 T

1 Reducer

2 4 inch nipples

1 8 inch nipple

1 nipple (1 pipe size smaller)

bushings (as needed)

1 Needle valve

1 Floor flange

 

The bushings help you size down from the 1.250/1.50 pipe to the .250 size of the needle valve. If you are lucky, you might be able to find a .250 to 1.250 in a single piece. Most often you need 2 bushings. I get my needle valves at a BBQ supplier online, though sometimes I can find them at hardware stores.

 

If you can find a blower like this one

those are the ones I like. The round flange is simple to mate to the floor flange, some nuts and bolts and a couple of holes drilled and you are done. If you have some other kind of blower, you'll have to kludge the connection yourself. 60-100 Cfm is the range you're looking for. I use a 100cfm fan for my forges (I bought 5 of them the last time Surplus Center had them) and it's really too much air. I have to choke my vertical forge down about 70-80%, even my welding forge only runs at about 50% air flow.

 

The burner parts

 

 

 

The burner in two different configurations

 

 

 

I have used both of these, and I can't say that I ever noticed a difference. When I was starting out I was told that the elbow promoted swirl and fuel/air mixing. I think having the fuel being injected into the air stream at 90 degrees to the flow creates plenty of mixing.

 

Some folks put a gate valve between the fan and the gas inlet to adjust the airflow in the burner. I use a bit of magnetic sign material over the intake on the fan. It does the same thing.

 

To operate this burner is pretty simple (see above). I have my forges (3 of them) connected to a black iron manifold, each forge has a 1/4 turn shutoff valve (in case you need to kill the forge fast) between the manifold and the needle valve.

 

Step 1: Pressurize the manifold (turn the gas tank on)

Step 2: Turn on the blower.

Step 3: Open the 1/4 turn valve

Step 4: Light the plumbers torch

Step 5: Open the needle valve

Step 6: Light the forge

 

When I first started, we used to ball up a piece of newspaper and stuff that in the forge and then turn on the gas and air. This resulted in a WHOMP and a ball of flaming paper shooting out of the forge, which always scares the new guys. Cool! Now I use a plumbers torch. By lighting it first you avoid any gas build up and the big WHOMP as the forge lights.

 

Troubleshooting

 

If the forge pops and goes out, add a bit more gas or shut some of the air down.

 

If the forge has big billowy flames coming out of it, turn the gas down.

 

Once you found the operating mix for your forge you can adjust the fire by opening and closing the air control, and by adjusting the gas flow with the needle valve. Most of the time you want just a bit of blue/green flame out the door of the forge. That means that all of the air is being burned in the forge (a reducing atmosphere) and the excess fuel is lighting as it hits the outside air.

 

This bit came up later in the thread, I've moved it here for simplicity.

I have found 2 ways to control the temperature with this burner. For my vertical forge I set the air (allowing about 20% flow) and vary the needle valve up and down. With my HT forge I want to be able to run at very low (for the burner) temps, in the 1450-1550 range. To get that I run the line pressure up to 8-10 psi, just crack open the needle valve and then fine tune with the air flow. I have gotten stable temps as low as 1380 F, which is pretty low.

 

One more thing that just occurred to me. I have had people build this burner and come back and say "I tried a test run and it doesn't work". The burner will not hold a flame in open air, it needs the case around it to work. Most of the venturi burners will burn on a test bench, and I think that people expect the same behavior in the blown burner. If you want to test your setup, build a brick box around the end of the burner, or use a roll of Kaowool. That should do the trick.

 

 

 

This topic is going to be pinned, so if you have questions, now is the time.

Edited February 7, 2013 by Geoff Keyes

[Brandon Buford]

No Questions, just a Great Big Thank You!

[Clifford Brewer]

Thanks for showin this Geoff, This answers a lot of issues I've had with my forge after going from a venturi side burner type

to a blown burner, the side burner never got to weld temp, and the blower type I put together don't quite get there either my blower looks similar to your suggested type but it is a squirrel cage type Fine for GP work but no welding ....

I'll try your set up as soon as money permits any input you can give would be greatly appreciated....

 

P.S. Ya gotta click on the pic to see all of it ...

Edited February 6, 2013 by Clifford Brewer

[Geoff Keyes]

Clifford,

 

I get welding temps in mine. I'd bet that the fan is the issue. As a test, put a shop vac blowing into the intake of the fan. If this supercharge gets you to a welding heat, that pretty much proves it. I don't think Klamath Falls is high enough for altitude to be a problem.

 

Two other thoughts.

 

You might shorten up the burner, it may be that all of the length of pipe is a problem (though I think a bit more fan would solve it).

 

I like to have the fan above the forge inlet. Propane is heavier than air. I blew up a fan by accidentally turning on the gas before the fan and getting a pool of propane in the fan housing. When the fan came on, it sparked and WHOMP, blew the case apart. Kind of a BTM (Brown Trousers Moment).

 

Geoff

[stealfdawg]

on the second set up have you tried swapping the blower and gas valve position so the blower is straight shot to the venturi created at the reducer? will this make any difference? the gas comming in from the center post of the T...other than having everything hanging waaay out the side of the forge do you think there would be any diffrence?

Edited February 7, 2013 by stealfdawg

[Clifford Brewer]

Clifford,

 

I get welding temps in mine. I'd bet that the fan is the issue. As a test, put a shop vac blowing into the intake of the fan. If this supercharge gets you to a welding heat, that pretty much proves it. I don't think Klamath Falls is high enough for altitude to be a problem.

 

Two other thoughts.

 

You might shorten up the burner, it may be that all of the length of pipe is a problem (though I think a bit more fan would solve it).

 

I like to have the fan above the forge inlet. Propane is heavier than air. I blew up a fan by accidentally turning on the gas before the fan and getting a pool of propane in the fan housing. When the fan came on, it sparked and WHOMP, blew the case apart. Kind of a BTM (Brown Trousers Moment).

 

Geoff

 

Thanks Geoff, The lack of air flow is what I was thinking also, as well as the final pipe diameter is too small, you recomend

1.25-1.250 if I got it right, and my final size is 1.125 from a 2.00 beginning I also have been very carefull about starting the fan first knowing the gas weight issue. As for the plumbing length I was looking to save space and this setup did save some but does cause a safety and BTM concern I will be doing a re-do on this soon as I can get a proper blower from surplus center

[Geoff Keyes]

The reducer is not creating a venturi. The whole system is under pressure from the blower. The reducer creates a restriction in the flow, increasing the density of the fuel/air mix. I have tried building these without the restrictor and the burn is soft and wants to crawl back up the tube. With the restrictor you can control the burn from a nice soft reducing fire to a hard crispy flame, which also changes the heat.

 

BTW, I forgot to mention in my first post, I have found 2 ways to control the temperature with this burner. For my vertical forge I set the air (allowing about 20% flow) and vary the needle valve up and down. With my HT forge I want to be able to run at very low (for the burner) temps, in the 1450-1550 range. To get that I run the line pressure up to 8-10 psi, just crack open the needle valve and then fine tune with the air flow. I have gotten stable temps as low as 1380 F, which is pretty low. I'm going to move this paragraph into the main body of the post for future ease.

 

Geoff

Edited February 7, 2013 by Geoff Keyes

[Clifford Brewer]

on the second set up have you tried swapping the blower and gas valve position so the blower is straight shot to the venturi created at the reducer? will this make any difference? the gas comming in from the center post of the T...other than having everything hanging waaay out the side of the forge do you think there would be any diffrence?

 

Dawg; The plumbing setup was a space saving attempt as the shop is small, swapping the blower and valve positions wouldnt work as the gas is heavier than air and will cause issues

[Jim Kehler]

On a side note I'd like to add that having the forge too reducing increases the carbon monoxide a lot according to my CO monitor.

If I set the flame just a wee bit reducing the monitor shows no CO. With a venturi burner I couldn't find any way to not have a lot of CO.

[Geoff Keyes]

Jim,

 

Thanks for reminding me about CO. I used to have a much smaller shop and I always had an exhaust fan running. My current shop is big, the hot shop is two stories and not very air tight, so I've forgotten about CO issues. If your shop is small and/or, fairly air tight, set up an exhaust fan and invest in a CO monitor. We don't want folks killed doing this stuff.

 

Geoff

[Don Abbott]

Geoff,

 

Man, thanks for the information. This is now toward the top of the project list. I love my coal, but it is very time consuming on those short evening forge sessions. I believe a gasser will eliminate some of my excuses.

While we’re here, and since this is a sticky, would you care to address the differences between the horizontal and vertical forges using this burner type?

 

Thanks again,

Don

 

 

[Geoff Keyes]

I've moved some information from the thread into the body of the first post, just to keep everything in one place.

 

G

[Geoff Keyes]

Don,

 

I'm happy to share this stuff, but it will be nice not to have to re-type it every month .

 

I use the same burner (well two burners, same design) on my vertical forge and on my welding forge (horizontal). The only difference is the tuning. On the vertical forge I set the line pressure at about 1 psi, close the air flap about 80%, and the regulate the gas with the needle valve. The forge comes up to heat in about 90 seconds, since it has no hard materials in it (it's just Kaowool in a case, with a thin layer of Satanite and ITC100).

 

For the welding forge I set the line pressure to 8-10 psi, open the air flap about 1/2 way and regulate the burn with the needle valve. Because the forge has a brick floor (to resist the flux) it takes 30 minutes or so to come up to heat. I usually try to have some other small projects to work on while it comes to a welding heat, just so I can feel like I'm not wasting gas for nothing.

 

You'd like to have the burner come in at an angle so that the flame swirls around the burn chamber. In the vertical forge it's easy, the inlet is at floor level, well below where your work is, so you get less scale no matter how the flame behaves. With the horizontal you have to aim the flame at a tangent to the wall of the case, I've never had all that much luck doing it. You can try stuff like building a baffle (an angled piece of fire brick right in front of the inlet), but for the most part, I just put up with a hot spot.

 

Geoff

[Clifford Brewer]

Geoff; Thank you again for this post I have re-configured my burner and was impressed with the difference

I get a good working temp at 2 psi and about 30% air and wicked heat at 8/10 psi and 75/80% air with this set up.

I'm gonna make a choke plate for the blower tomorrow as duct tape wont cut it fer long, got so happy I made a new pair of tongs

with my improved system... (see pics)... ( OH Yeah ! it's the same blower too, go figure,,, )

 

Edited February 9, 2013 by Clifford Brewer

[Geoff Keyes]

Cool! Glad to help. So what was the fix, do you think?

 

Geoff

[Clifford Brewer]

Cool! Glad to help. So what was the fix, do you think?

 

Geoff

 

I'm thinkin elimination of all that extra plumbin was the major help, ( too much volume I suspect ) that and puttin the gas below the blower did'nt hurt either.... Now to see if I can finally forge weld....

Thanks much Geoff ..Hammer Happy !!!

Edited February 9, 2013 by Clifford Brewer

[Don Abbott]

OK, one more...

 

Where the burner pipe goes through the shell of the forge, does it fit tight, is it sealed, or is there an air gap?

[Geoff Keyes]

You can cast a nozzle in mizzou, I just stuff some kaowool scrap around the injector end. If you have a gap, you tend to get flame blowing back around the nozzle. It probably doesn't hurt anything, but I don't like seeing it.

 

Geoff

[Brian Madigan]

Dang! Surplus Center just ran out of those nice blowers. I had one in the shopping cart (there were 9 left) to replace the loud-ass shop-vac blower.

One thing I do instead of blocking the blower intake is to have an inline T-joint bypass with a gate valve after it. To increase air flow, open the gate valve, to decrease, close it and the air bleeds off to the open side of the T.

That way the fan runs at constant load regardless of how much air you need. The air bypass/gate valve is always situated Before and Above the gas inlet!!

It's a good idea to design any blower such that if the blower goes off before the gas does, the gas doesn't fall into the blower, but rather into the forge to be burned. The blowers aren't explosion proof, so if they get gas in them they're likely to grenade.

just another note: CO fills your space from the top down. Even if you have a door open, the gas fills up the space like an upside down swimming pool. I noticed this once, almost too late. I had a forge running inside a large garage, with the 12x8' overhead garage door and a rear door open for a cross-breeze. This was not sufficient. I basically had my head in an upside down pool of CO. If CO could be visualized, imagine it was pouring out of the doors and rising into the atmosphere. However my head was above the door, under water so to speak. This could have killed me, even though the CO meter wasn't going off.

[Geoff Keyes]

Further Safety Note

As I said above, I use 1/4 turn shutoff valves on my burners. I put them between the needle valve and the gas supply ( in my case I have a manifold that feeds 2 walls of the shop).

 

My Lady Wife and I were talking about this post and she said that everyone in the household should know where the shutoff to each piece of equipment are and how to use them. Further, they should all actually shut the gas/machine/power off, not just know that you can. Have them actually do it. That way, if something should happen to you (the normal operator), they can kill the system. I think this is really good advice. We work with dangerous stuff. Gas, forges, high temperatures, flammable stuff, dangerous machinery. The people who might need to save you need to be able to make the environment safe before starting rescue operations. This also goes for visitors, students and anyone else who is in the shop. At the very least, they need to know where the exits are.

 

Stay save and be aware.

 

Geoff

[Alan Longmire]

This is actually where it can kill you twice. CO at room temperature is heavier than air. You can actually carry it around in an open pitcher and use it to snuff a candle in a bowl just by pouring it in to displace the oxygen. CO from a forge is hot, so it rises and fills the room as you said. Then guess what? It cools off, and sinks as it does. The CO meter needs to be where your head is, as close as possible to where you stand while working.

 

just another note: CO fills your space from the top down.

[timgunn]

I think you've missed the all-important 2 Alan.

 

It's CO2 (Carbon Dioxide) that's heavier than air and will extiguish a candle. Its Relative Molecular Mass is 40. The RMM of air is about 29.

 

CO (Carbon Monoxide) is a little lighter than air and is a flammable gas. Its RMM is 16.

 

The differences between the RMMs of CO2, Air and CO are not all that great. As a result, little or no separation will normally occur over the sort of timescales that we are usually concerned with. This is partly due to the fact that, in our application, both CO and CO2 are produced along with lots of heat and even hot CO2 is lighter than cool air, so will tend to rise.

 

Neither CO2 nor CO is healthy to have around: CO2 is usually present because the Oxygen in the air has been burned with a Carbon-containing fuel (or respired by a life-form; it is present in a concentration of 3-5% in the air you normally breathe out). The main risk from CO2 is usually considered to be the lack of remaining Oxygen in the air, causing asphyxiation.

 

CO kills at much lower concentrations. It binds tightly to the Oxygen-carrying locations in the red blood cells, preventing them doing their normal job of carrying Oxygen to where it is needed. It's worth bearing this in mind; CO attaches to the Oxygen-carrying sites much more readily than it leaves them; going outside for a short breather during a forging session will not actually do much to reduce the blood CO level once it has been raised.

[Alan Longmire]

I sit corrected! Tim is correct. Ventilation is still your friend.

[Richard Furrer]

I prefer blower systems...I use one now with a router control rheostat from harbor freight for $20. Make sure you have a brushed motor.

The blower runs quite at lower speeds and you can leave the gate open.

 

I caution about having the blower above the forge or too close. I have killed motors due to radiant heat.

When I run for long periods or the crucible furnaces I place insulating blanket between the forge and the blower.

On rare occasions I move the large shop fan close to the blower to cool it. This also dilutes and moves the exhaust air and if I get the angle right can save the hair on my arms.

 

Many forges run well for an hour of so...when you have it on for ten hours you find many things are not right with the world. My forges are not near the walls or under anything that can get hot. My ceilings are 20 foot up and the thermometer I have at the peak reads 80F in the coldest winter when the forge is on for an hour. At four hours it is 120F and I open the door wider and try to dump heat....or at least move it to the far corner of the shop which never seems to get warm.

 

 

As an aside...I have thought about running a passive glycol heat exchanger from the shop ceiling over to the house to heat whatever when I am forging. If anyone is up to speed on such things I'd like to talk to them.

 

Ric

[Andrew Ashley]

I am relatively new to the trade, and have only used coal so far. Looks like thats about to change! Thanks Geoff for the info. I am so excited to get a propane forge together.

 

~Ashley