Running a forge on house pressure

[Judehey]

I just got a propane furnace for the house. The tank is not installed yet,  but it will be right by the shack where I have my forge, and they said it's easy to run another line. They say they are required to put a regulator on it, dropping the pressure to 5 or 10 psi, they weren't sure which. That should be enough for my forge,  but should i continue to use my normal regulator in tandem? Or should I rig up a needle valve?  I'll be in the same quandary with my oxy-propane torch. 

Thanks

[ThomasPowers]

First check what pressure they will be providing.  Appliances are often rated in "Water Column inches" where 32 *feet* = 1 atmosphere or  26 inches equals about 1 psi

[Mikey98118]

Even if you are limited to such low gas pressures, you can still run a forge with the help of a fan; just as you would with natural gas. Nevertheless, that propane will produce about one-third more usable heat. Since natural gas forges have been getting more than hot enough to run commercial forges forever, how much more with propane?

There are real problems that require careful answers, and then there are apparent problems that amount to nothing; this is what you face.

[JHCC]

There are a couple of threads about this already. See if you can find one with comments from IFI member Latticino; he’s the recognized expert. 

[Judehey]

 

The pressure will be 5 PSI maximum, so it looks like I will be building a blown burner.  I've read as much as I can find here and on other sites, but still have some questions.

Do I still need a regulator, or is a needle valve with the 5 PSI sufficient?

Is there are rule of thumb for burner area per forge volume?  My forge is a Devils Forge, ~15 square inch by 16 long, ~230 cu in.  I have 2 ~3/4 venturi burners, which is a bit overkill, I usually only use one of them. I will still want to have 2 burners for heat distribution (plus I already have the two ports), but I don't know what size pipe to use.

Some of my proposed design is based on a video from ChristCenteredIronWorks, including the mitered 90 degree bends and the end plate.  The design in the sketch doesn't allow for using only a single burner.  If I run two fuel lines to be able to use a single burner, Do I need to be able to shut off the air to the unused burner, or just the fuel?

I have a variable speed bilge blower left over from another project.  Is there any reason that would not be adequate?  Max flow, is 240 CFM, but I would reduce that with the variable speed and dump port.

I probably have many more questions, but this will get me started. 

Thanks, Jude

 

[Mikey98118]

You seem to be missing the point. A five PSI gas input is barely enough to run a naturally aspirated burner. Thus, the talk of fan-blown forges.

A fan blown forge with 5 PSI does need a valve on its gas line, to vary pressure; otherwise your forge would only have one heat range; full blast. Forges running natural gas on house pressure (about 1/2 PSI) can use the fan alone to vary temperature range. Even then, I would install a gate valve on the gas line, to vary input, instead of a ball valve (open/closed).

[Frosty]

I don't even want to start pointing out the mistakes. This is too dangerous to try figuring our yourself starting with as little knowledge and understanding as your drawing shows. There are components in the wrong order, one dangerously wrong.

If an inspector gets ONE LOOK he'll put a lock on your tank and you're whole house will be shut down until it's removed and cleaned up by a certified service company.  Just because someone, even a licensed service tech says a thing CAN be done doesn't mean much if you make a hash of it.

I'm not trying to discourage you, I just don't want to hear about you burning your place down and your insurance denying the claim for cause. NO insurance company will pay a claim that involves a home made gas burning appliance, even if it had zero to do with the claim. Just having one in the same building is a deal killer.

Frosty The Lucky.

[Judehey]

I'm glad I asked. This was based on what I was able to find. Could you please point me in the right direction?

[Frosty]

Just so you know up front I'm not a gun burner guy, the T burner is mine and if I were I you I'd put two 1/2" T burners on your forge and use a propane tank and 0-30 psi regulator. That would let you get completely away from the house and it's tank so all the insurance company would do is tell you to get rid of it. 

But if you wish to use a gun burner (blown) then I suggest using ungalvanized plumbing pipe. Welding the joints is just adding more failure points, over complicating things is never a good thing. Keep it simple. 

Connect the blower to a pipe roughly the same diameter as it's outlet and then connect it to one that will go to the pipe that mounts your burners. A pair of 1/2" pipe burner nozzles is too much gun for a 230 cu/in forge but you can turn them down. 3/8" nozzles might be better but I don't know, 1/2" is more than enough I like conservative designs. 

Are the burner ports actually mounted center top aimed straight down as drawn? If so that's a bummer, I don't suppose you want to drill a couple more holes in the forge do you?

Anyway. If you mount the nozzles in the indicated positions and put a 90* elbow on each aimed at each other then connect a T and two short nipples that reach the elbows. I'd run 1 1/2" minimum from the blower to the T fitting and again to the elbows. I don't know if a 1 1/2" x 1/2" elbow is available but that'd be perfect.

Screw all this together and you have a simple U shape large pipe with two small ones poking down into the forge, maybe visualize a log bridging two round fence posts. The pipe between the nozzles will be a plenum which will allow the pressure to equalize so both nozzles have matched flames. Make sense?

The fuel air mix will enter through a "Supply pipe" running between the blower and the T fitting. Your gas will be introduced to the flow immediately AFTER the blower pipe necks down to the supply pipe diameter through a small diameter pipe, say a 1/4 nipple. You don't need to drill a particular jet size just the open end though you CAN cap it and drill a 1/8" hole but you only have 5psi. so leaving a large opening will ensure it will supply enough propane. A needle valve on the propane supply line will control the fuel flow. You can forget about a gauge or another regulator. Gun burners do not depend of fuel pressure, they require controlled volume. I can explain that if you like but later, okay?

What will happen is the air from the blower will build to it's rated static pressure in the large pipe the blower is connected to. I'm assuming it is a "transparent" blower so it just stops moving air once it reaches max static pressure. (If it is an Opaque blower it WILL NOT WORK!) I'll explain later. As the flow enters the smaller supply pipe it will accelerate and the propane will be introduced a couple inches down stream. The air & fuel will mix as it travels up the supply pipe and when it reaches the plenum it will slam into the far wall and become VERY turbulent. This turbulence will finish mixing the air and propane nicely, the pressure in the plenum will equalize and discharge through the 1/2" nozzles equally and burn in your forge. 

I'm not familiar with bilge blowers so I'll explain the difference between transparent and opaque blowers. A "transparent" blower is basically a type of fan in a housing, air will move freely through it if it isn't running and if it is running you can block intake out outlet and stop the flow completely without damaging anything. This is what's needed here.

An opaque blower is a positive flow device if it's not running air will NOT flow through it. If it is running blocking the outlet will either stall the motor or explode something in the circuit. Block the intake and it will draw a vacuum. 

If you've ever watched a dragster blow the bug catcher a couple hundred feet in the air you've seen a Roots Blower get blocked. Roots Type blowers are the definitive example of an Opaque Blower. 

The ONLY way to control the output of an Opaque blower is either by the speed of the motor driving it or through a waste gate. 

This is why I ASSUME bilge blowers are transparent blowers. 

I hope that's less confusing than trying to draw pictures with text usually is. My comp isn't accepting scans from our printer scanner and a cell phone pic emailed to it is bouncing. I can't make sketches and none of my cad software is worth spit. I hate rendering when a simple line drawing explains things. 

My computer had a major software crash about a month ago and spent 4 days in the shop and another week getting everything working again. Now it's starting to act twitchy again.

If I don't answer your questions I am NOT ignoring you my comp may be dead lined again. I WILL get back to you if this thing dies again, maybe on a new computer but I'll get back. 

Frosty The Lucky.

[Latticino]

Frosty,

Well I've been in the business for a little while and have heard of a lot of different kinds of blower: centrifugal, forward inclined, backward inclined, radial, vane axial, mixed flow, plenum, squirrel cage, sidewall, high pressure/low flow, low flow/high pressure, high plume lab exhaust... but I've never heard of transparent and opaque blowers.  Did you coin those terms?  Do they have a reference for a particular application (like bilge blowers being used to exhaust out boat enclosures)?

As I've mentioned before blowers or fans need both a airflow and external static pressure rating at a number of conditions to establish a fan curve.  In my experience, for "gun" burners, the better choice is one that is relatively high pressure and low flow (typically, in the hobbist world, a centrifugal fan with an radial impeller)

Some examples from the fabulous interweb...

 

[Mikey98118]

This is a serious question; not an attempted  wise-crack. How would you classify today's computer fans?

All I can come up with so far is that they seem to have impeller style blades.

[Latticino]

Mikey,

More often than not these will be axial fans (at least if you mean the ones shown in the first picture below).  Whether they are called tube axial or box axial appears to be a matter of length of the casing.  Some manufacturers will call these mixed flow fans due to the geometry of the impeller, but essentially they will fall under the general umbrella of axial fans IMHO.  By the way, as I understand it the word "impeller" refers to the function of a fan or blower blade, not it's configuration (used to move, or "impel" the fluid from one location to another.  Note this same designation is used for the "business" part of most pumps)... 

While families of fans do tend to have common defining characteristics, the real key to proper fan selection is to review a fan curve and chose one that properly matches your distribution system (system operating point intersecting with a stable, efficient and quiet (if possible) point on the fan curve.

 

Also note that some computer elements are cooled with centrifugal fans, which can be subcategorized as forward curved, backward curved, airfoil...

 

[Mikey98118]

Latticino,

Yes; the one shown in the first picture above is the type I have been using on what I describe as vortex burners. One of the problems that come along with repurposing equipment for novel uses is a lack of technical information to "cut and paste" into my descriptions of them

However,

4 hours ago, Latticino said:

By the way, as I understand it the word "impeller" refers to the function of a fan or blower blade, not it's configuration (used to move, or "impel" the fluid from one location to another.  Note this same designation is used for the "business" part of most pumps)... 

All that directly relates to their particular purposes on this series of burners. Thanks for your input.

[Frosty]

I don't have a cite for the descriptions opaque or transparent blowers. I read it many years ago when I asked one of the mechanics too many questions about different types of super chargers he gave me one of his books to read. One of our trucks had taken a dunk in a small boat harbor while running and the Roots blower had suffered a hydraulic lock and blew a hole in the inner fender of the truck. The turbo charger was unharmed by sucking water even when the roots locked and blew. 

A turbo charger is "transparent" to flow. If one locks up the exhaust can flow uninhibited as can the intake air so the engine can still run. 

A roots blower is a Positive displacement pump using intermeshing lobes. Visualize elongated gears meshing as they rotate air or liquid is caught between meshing lobes and as they rotate it MUST go along until the lobes open and the liquid is released. If the intake is blocked a roots type pump WILL draw a vacuum. Block the output and it will stall the drive motor or explode. Nothing can pass through an "Opaque" pump if it is not turning. A piston pump is opaque.

I didn't coin the phrase it came right out of a basic mechanical type book about super chargers. I started seeing it more often or maybe realized what they were talking about. A lot of the other mechanics in the heavy duty shop called them positive vs. free flow super chargers.

They're the terms I learned when I first learned the difference so maybe so far out of date as to be archaic. They don't really lend themselves to an intuitive connection of pumps. I'll try to remember to use positive vs free flow. 

Do you know of a proper term other than positive vs. free?

Frosty The Lucky.

[Latticino]

Frosty,

I'm afraid that you have come to my limit in fan/blower design terminology.  I've heard of overloading and non-overloading fans (which basically has to do with fan system effects on the driving motor), but I've never heard or seen the terms positive vs free flow, or transparent vs. opaque used in the HVAC field as a description for fans or blowers, and I've been in this on and off since the early 80's.  Doesn't mean it isn't common for specific trade applications (automotive for example), or something that a blower designer might be aware of.

Some good bullet points regarding fan design in this ASHRAE PowerPoint presentation: https://rockymtnashrae.com/downloads/2012_Tech_Conference/introduction_to_fans___ashrae_4_20_12.pdf

 

[Frosty]

We dealt with way different types of pumps, most of what I worked with on the job were positive flow like progressive cavitation, "Moyno" was the maker we used, also known as "peanut butter pumps." We used moynos to put water or drill mud down the hole. We used an impeller "trash" pump to transfer water to the mud tub from the source if it wasn't close enough to drop the moyno's suck hose in the creek, etc. 

The other pump's innards I became TOO familiar with were hydraulic pumps and motors which are roots type pumps. Each drill had one primary hyd. pump and up to 6 motors. The new (in the 80s) CME drill rigs had more than 1/2 mile of hydraulic lines, WAY too many hoses to be efficient entropy wise. Valves, fittings, restrictor valves, hyd. cylinders, etc. etc.

And THAT triggers my memory of where I saw transparent vs. opaque pumps, the maintenance and repair books for the old Mobile, B-26, Pacemaker, drill rig! Old as in 1967. We worked in remote locations so we had to do a lot of the mechanical work on our rigs ourselves and we had all the books in a weather tight case in the cab or a tool box. 

There were no hydrostatic pumps on our rigs so I only know how to recognize one and have no interest. Other than they ARE opaque in 1960s hydraulics terms.

This stuff is starting to come back, now I gotta go do something to help forget. 

Frosty The Lucky.

[Mikey98118]

I have been retired for twenty-six years, and still play audio books all night, just to keep from trying to resolve all the catch 22 situations. during sleep, that made work so nasty during the last two decades of it. Given the choice, I'd rather have nightmares.

[Frosty]

I made a good move transferring out of the geology section to road maintenance for my last 10 years. You can't live with the same two guys 24/7 sometimes 3 weeks straight and not hate everything about them. They were good guys, we always had each other's back but it really wears on you. Sometimes we'd hardly talk more than necessary while working and not at all after work. Changing to road maint. let me start wearing out different parts of my body and there were about 32 guys +/- on the crew. Even when we were working small crews say repairing guardrail, ditching, patching potholes, etc. we could change crew by asking. You're going to have friction of course but you weren't stuck sucking it up.  

I do kind of miss getting to play with the hydraulics like I got to on the drill crew but I don't miss the drill crew at all.

Frosty The Lucky.

[JHCC]

7 hours ago, Frosty said:

You can't live with the same two guys 24/7 sometimes 3 weeks straight and not hate everything about them.

The Soviet-era Russian dissident Vladimir Bukovsky noted in his memoirs that "You can safely divide all of humanity into those you could share a cell with and those you can't. Unfortunately, in prison, you're not given the choice."

[Andrew LB]

On 6/21/2022 at 6:17 AM, Latticino said:

Mikey,

More often than not these will be axial fans (at least if you mean the ones shown in the first picture below).  Whether they are called tube axial or box axial appears to be a matter of length of the casing.  Some manufacturers will call these mixed flow fans due to the geometry of the impeller, but essentially they will fall under the general umbrella of axial fans IMHO.  By the way, as I understand it the word "impeller" refers to the function of a fan or blower blade, not it's configuration (used to move, or "impel" the fluid from one location to another.  Note this same designation is used for the "business" part of most pumps)... 

While families of fans do tend to have common defining characteristics, the real key to proper fan selection is to review a fan curve and chose one that properly matches your distribution system (system operating point intersecting with a stable, efficient and quiet (if possible) point on the fan curve.

 

wow. An Ys Tech TMD (tip-magnetic-drive) fan. Never thought i'd see one of those again. That little fan is the result of a great idea that just didn't pan out for an assortment of reasons, but mostly due to axial fans just being such a good design. These kinds of fans, as well as axial fans are not what should be used in a forge.

I'm in the process of building a new forge and was considering a blown ribbon burner and saw how expensive most blowers people tend to use are, but for how big and expensive many of those blowers are, the specs aren't really all that great. A popular forge blower fan i looked at had the following specs.

• 125 CFM when damper is full open
• 2.7" H20 (mmAq) - 69mm
• 2" opening
• $125
• 110v ac

Considering how it seems static pressure is more important than CFM for a forge, here is one Sunon fan i thought would work for a smaller ribbon burner.

• 44.2cfm
• 3.39" H2O (86mm) static pressure.
• 12vdc
• 1.25" opening
• fan type: blower
• $22 @ digikey.

I use a slower version of that Sunon blower connected to a PID controller and thermocouple to control my 55 gallon drum smoker for making sweet sweet bbq.

 

 

Also, Frosty... you've got some interesting fan terminology there. Most of which i've never heard before.

[Frosty]

In what way? Unless you use the broadest sense of the term an opaque hydraulic or hydrostatic pump isn't a fan of any description. Technically anything that moves something is an impeller, say a, Colt revolver, Falcon Heavy rocket or a Honda Civic.

I admit I got sidetracked talking about the difference between "transparent" vs. "opaque" pumps. It was a good term, made perfect sense if you were routinely up to your elbows in hydraulic parts and fluid but I haven't seen it used in I don't know how long even in hydraulics manuals.

"Transparent" meaning the fluid being impelled can move through the pump even if it's not being powered. It is "transparent" to flow. 

"Opaque" meaning nothing can flow through it unless it is under power, eg piston pump. It is "opaque" to flow.

Fans are by their nature "transparent" impellers.

And thank YOU very MUCH for dredging those memories up this morning. Just what I need, a brain worm, I don't have anything useful to think about. <sigh>

Frosty The Lucky.

[Mikey98118]

Andrew,

I only use axial computer fans with impeller blades to induce air into the vortex burner design. Fans used to blow air into a forge, or into a ribbon burner's plenum chamber need to create positive air pressure; and adding to a linear burner's air pressure is the last thing I desire.

On the other hand, your objection to most of the fans used in forges makes complete sense to me. I see no reason to pay out big bucks to install a high output fan on a burner system that can't use all that air; it is very poor engineering to my way of thinking.