Propane orifice size

This forum is dedicated to the Live Steam Hobbyist Community.

Moderators: cbrew, Harold_V

Post Reply
cp4449
Posts: 569
Joined: Tue Jun 06, 2006 10:54 am
Location: Granada Hills

Propane orifice size

Post by cp4449 »

What is the oriface size for propane burner that most of you using? My oriface on my burner got damaged, I got a new one, but they sent one with a guide hole. I normally run at 5-8 psi, slot burner
Christopher P. Mahony
Los Angeles Live Steamers
1 inch scale member
User avatar
ChipsAhoy
Posts: 319
Joined: Wed Feb 18, 2015 12:23 pm
Location: Arizona

Re: Propane oriface size

Post by ChipsAhoy »

The Marty burners that I'm playing with use a #71 which is what the instructions call for. He goes on to say .....as close to .026 as possible. Now, he is working with 1 psi and up to 5 psi. One nozzle. The two that I have made so far appear way too rich, but I suspect that is poor machining and the design is fine.

The Wendy has a slot burner, I have not built one yet.
It has one #40 orifice feeding 4 ea. 10 inch tubes with 21 slots per tube.
I intend to build one and see what it does.
Scotty
rkcarguy
Posts: 1730
Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: Propane oriface size

Post by rkcarguy »

I always recommend trying some carburetor jets from something, so you have some adjustment. For example, the jets for the 6.5HP clone engines are around $1 each. If you drill and tap a brass pipe cap so the jet can be threaded in from the inside, you'll get a really nice dispersion of "gas" that will burn very well. # drill bits have some gaps in that size range, so I had the same problem racing go karts and trying to drill the jets....one size is too lean, next size is pig rich.
User avatar
ChuckHackett-844
Posts: 232
Joined: Wed May 03, 2017 3:54 pm
Location: Tampa, Florida

Re: Propane oriface size

Post by ChuckHackett-844 »

(I assume we are talking about a 'furnace' type burner, i.e.: one orifice, one mixing tube feeding a single manifold)

To calculate the orifice size you need to know how many BTU your burner can produce. From that, and knowing the pressure you want to feed it, you can calculate the orifice size that will deliver the given BTU at that pressure. .. or ...

Start with a small orifice and work your way up (adjusting the primary air inlet as needed) until, at full fire, the flame starts lifting from the burner - that's your limit.

That limit can be reached with many pressure/orifice size combinations. A large orifice at a low pressure will deliver the same BTUs as a small orifice at high pressure. This is why, asking someone "what burner pressure do you use" is meaningless unless you are using the same size orifice.

It is more desirable to use a smaller orifice at higher pressure because it does a better job of drawing in primary air and promoting mixing. There is a limit however because once the gas velocity through the orifice reaches the speed of sound a pressure wave is formed and the flow will not increase with a further increase in gas pressure.

For each burner configuration there is a maximum gas flow volume it can handle and thus a maximum BTU. The propane/air "flame velocity" (how fast the flame front propagates) is fixed for any given propane/air mixture ratio. When the gas velocity coming out of the holes/slots exceeds the "flame velocity" the fire will lift from the burner and, if you keep going, go out.

Hope that helps ...
Regards,

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
Owner, MiniRail Solutions, LLC, RR Signal Systems (http://www.MiniRailSolutions.com)
"By the work, One knows the workman"
cp4449
Posts: 569
Joined: Tue Jun 06, 2006 10:54 am
Location: Granada Hills

Re: Propane oriface size

Post by cp4449 »

OMG, the best explanation of this subject I have read. I never thought of carb jets. Good idea. Chuck, your write up was great, and I have two orifices I can drill. They are currently .71, I will start with that and work my way up until at a set pressure, lift the flame.
Christopher P. Mahony
Los Angeles Live Steamers
1 inch scale member
Berkman
Posts: 679
Joined: Wed Aug 16, 2017 7:55 pm

Re: Propane oriface size

Post by Berkman »

Have a photo of the burner you use in your northern Chuck ? Thank you in advance.
SteveM
Posts: 7763
Joined: Mon Jun 27, 2005 6:18 pm
Location: Wisconsin

Re: Propane oriface size

Post by SteveM »

cp4449 wrote: Wed May 23, 2018 9:10 pm OMG, the best explanation of this subject I have read.
I was thinking the exact same thing as I read Chuck's post.
ChuckHackett-844 wrote: Wed May 23, 2018 7:48 pmTo calculate the orifice size you need to know how many BTU your burner can produce. From that, and knowing the pressure you want to feed it, you can calculate the orifice size that will deliver the given BTU at that pressure
What is the calculation, or are there some tables or an online calculator we can use to get a starting point?

Steve
RickBarb
Posts: 63
Joined: Sun Jan 05, 2003 2:12 pm
Location: Cape Cod, MA

Re: Propane oriface size

Post by RickBarb »

Hi, I hesitate to join in on this thread as my attempt to gas fire my 3-1/2 scale Rob Roy have for the most part been unsuccessful. My problem is that I think I am trying to put 10# of stuff in a 5# sack. The firebox is 2"x3-9/32". I am guessing I need approximately 16,000 btu. I am close, but not yet successful. Now as for orifices, I have used "misting nozzles". They have a .012" hole that can be enlarged to whatever diameter you want. They are brass construction and are dirt cheap. You can buy on eBay 20 pieces for $6 to $8 from china, free shipping. How do they do it? For calculating heat output for pressure and orifice size I use an interactive calculator by: Thomas Vincent @ http://ronreil.abana.org/BTU_Calculator.xls. You just enter orifice diameter and coefficient and pressure and it calculates the output in btu's. Hope this helps. Any suggestions for me to try.

Rick
User avatar
ChuckHackett-844
Posts: 232
Joined: Wed May 03, 2017 3:54 pm
Location: Tampa, Florida

Re: Propane orifice size

Post by ChuckHackett-844 »

I have drawings, photos, etc. for the burner in my Northern but I don't know how to post such here. If you send an email to misccdh@whitetrout.net I can email you a copy.
Regards,

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
Owner, MiniRail Solutions, LLC, RR Signal Systems (http://www.MiniRailSolutions.com)
"By the work, One knows the workman"
Post Reply