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Old 06-03-2012, 09:19   #1
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Converting CNG to LPG

My next project was to remove the Shipmate 2 burner stove and clean it. I noticed on the back of it, someone had written in red marker NAT. GAS. I'm assuming it is jetted for natural gas. So I have a couple of questions...
1) If I hook it up to LPG (outside of course) what should I see when I light it?
2) Is it just a matter of drilling out some jets? Or do the holes need to be smaller?
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Old 06-03-2012, 09:36   #2
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Re: Converting CNG to LPG

Natural gas has much less energy per unit volume than propane (as propane molecules are heavier because they are longer chains, thus more fuel). If it were burners, you *might* be able to get away with keeping the burners turned down real low. In an oven, the thermostat isn't going to account for the hotter burn of the fuel.

I can tell you I've been to numerous fires where someone has rented out a space to a family that has brought in an old natural gas clothes dryer and hooked a propane tank up to it. I have a CNG stove/oven in the current boat, and it has a thermometer set up to read through the glass because the thermostat is all over the map. The cooktop works great, but we pretty much use the oven to store pans (which we can do now that we converted to electric, before with the diesel the rattle would remove fillings).

That being said, the orifices for propane are much smaller than those for natural gas, so you would have to replace them, not drill them out. It's much easier to go from propane to CNG than the opposite. My first BBQ conversion I was silly enough to buy the conversion kit thinking I'd get the proper orifice in there. Turns out it was just a hose, and the conversion was to just remove the orifice and run wide open. Ten minutes of Internet research would have saved me $50. Lesson learned.

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Old 06-03-2012, 09:39   #3
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Re: Converting CNG to LPG

Quote:
Originally Posted by Celestialsailor View Post
My next project was to remove the Shipmate 2 burner stove and clean it. I noticed on the back of it, someone had written in red marker NAT. GAS. I'm assuming it is jetted for natural gas. So I have a couple of questions...
1) If I hook it up to LPG (outside of course) what should I see when I light it?
2) Is it just a matter of drilling out some jets? Or do the holes need to be smaller?
If you contact the manufacture of your stove, they may have new jets to convert over to LPG.>> ShipMate Stove Company Inc. - your source for classic solid fuel boat stoves, heaters and sinks.
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Old 06-03-2012, 10:19   #4
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Re: Converting CNG to LPG

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If you contact the manufacture of your stove, they may have new jets to convert over to LPG.>> ShipMate Stove Company Inc. - your source for classic solid fuel boat stoves, heaters and sinks.
Ya...tried that number but just got a message. The site seems to indicate a new owner. Not sure. If it meant going to a smaller orifice, being a Machinist, I could solder them up and re-drill if I knew what the percentage factor was on hole size. If all else fails, I could buy and adapt new burners.
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Old 06-03-2012, 10:28   #5
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Re: Converting CNG to LPG

I do know the orifice needs to be smaller for LPG, maybe by 1/2. If you could make new ones and start out extra small and try them out, then increase the drill size .005" (or number drills) at a time until ur happy. On some stoves too there is a air baffle that regulates the air intake into the feed tubes, that may need to be adjusted.
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Old 06-03-2012, 12:09   #6
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Re: Converting CNG to LPG

Sounds like a good starting point...thanx
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Old 06-03-2012, 13:19   #7
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Re: Converting CNG to LPG

"In an oven, the thermostat isn't going to account for the hotter burn of the fuel."
Actually, a thermostat shouldn't care about the fuel, it should be simply closing the fuel supply off to cool things down, and opening it up to heat things up. Responding to the heat without regard to the type of fuel.

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I wouldn't SOLDER in stove parts. Not even in the 'cold' parts. Tack weld maybe, or peen it out to close it up, but soldering in a "machine" that is designed to get real hot, and sometimes accidentally gets hotter? You know, that can absolutely ruin your dinner plans.

CNG: An answer in search of a problem, all too often. At least, here in the States. Then again, when I asked the man from thegads company why I couldn't ever get a nice blue flame on my home stove burners, he kinda scratched his head and said it just MIGHT be so old it was jetted for "coal gas" and not what is in the city gas lines these days at all.

Coal gas?? Sometimes, you don't want to ask.
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Old 06-03-2012, 13:50   #8
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Re: Converting CNG to LPG

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Originally Posted by hellosailor View Post
"In an oven, the thermostat isn't going to account for the hotter burn of the fuel."
Actually, a thermostat shouldn't care about the fuel, it should be simply closing the fuel supply off to cool things down, and opening it up to heat things up. Responding to the heat without regard to the type of fuel.

Celestial-
I wouldn't SOLDER in stove parts. Not even in the 'cold' parts. Tack weld maybe, or peen it out to close it up, but soldering in a "machine" that is designed to get real hot, and sometimes accidentally gets hotter? You know, that can absolutely ruin your dinner plans.

CNG: An answer in search of a problem, all too often. At least, here in the States. Then again, when I asked the man from thegads company why I couldn't ever get a nice blue flame on my home stove burners, he kinda scratched his head and said it just MIGHT be so old it was jetted for "coal gas" and not what is in the city gas lines these days at all.

Coal gas?? Sometimes, you don't want to ask.

Then being brass (I assume) I could plug them with a press fit plug and redrill...That was a good point
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Old 06-03-2012, 14:21   #9
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Re: Converting CNG to LPG

Brass...plug fit...I trust threads more, or a real firm press fit that you were sure couldn't eventually work its way out after thermal cycling a couple hundred times.

But that's just me, I don't trust anything mechanically more complicated than a whiskey cork, and I have a firm fear of fire.<G>
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Old 06-03-2012, 14:57   #10
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Re: Converting CNG to LPG

If the plug was .100", I would use a .0015" press. Keep in mind that the thermal expansion for both body and plug is the same. Although I have not accessed the orifice's yet. It may be as easy to machine an orifice blank and start from scratch. We're probably talking 2 hours for 3 orifice's. I know that would take away from my 3 hour nap here at work but we do have to make sacrifices once in awhile...
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Old 06-03-2012, 16:27   #11
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Quote:
Originally Posted by hellosailor
"In an oven, the thermostat isn't going to account for the hotter burn of the fuel."
Actually, a thermostat shouldn't care about the fuel, it should be simply closing the fuel supply off to cool things down, and opening it up to heat things up. Responding to the heat without regard to the type of fuel.

Celestial-
I wouldn't SOLDER in stove parts. Not even in the 'cold' parts. Tack weld maybe, or peen it out to close it up, but soldering in a "machine" that is designed to get real hot, and sometimes accidentally gets hotter? You know, that can absolutely ruin your dinner plans.

CNG: An answer in search of a problem, all too often. At least, here in the States. Then again, when I asked the man from thegads company why I couldn't ever get a nice blue flame on my home stove burners, he kinda scratched his head and said it just MIGHT be so old it was jetted for "coal gas" and not what is in the city gas lines these days at all.
I understand that in theory it shouldn't matter what the energy density of a fuel is for the thermostat. But I'd be willing to bet that while it might work, it won't function properly. I know mine doesn't light immediately, and tends to go "whoosh" (that's a fire service technical term) even with the proper fuel. And assuming it lit properly, I don't think you'd get a usable temperature maintained, because it would be heating up much faster, and probably blowing right by the target temperature. Heck, mine cooks way over temperature (sometimes) and its using the right fuel.

CNG is a bummer for me because of the higher storage pressure requires a tank hydro, and the nearest source is 30 miles away. Oh, and while not boat related, it's hard to get a really good sear on my natural gas BBQ because it just doesn't burn hot enough. Although that can be a good thing:


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Remember kids, don't try this at home, and really don't try it with propane!
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Old 06-03-2012, 16:46   #12
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Re: Converting CNG to LPG

On a related note - my boat has a pristine stove with a tank - pressurized alcohol or diesel? How can I convert that to propane? Hate to throw away a stove in good condition and spend $1000+ to replace it.
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Old 06-03-2012, 17:10   #13
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Re: Converting CNG to LPG

Been there done that. Here's a post I made showing at least the photos of my conversion.

CNG to Propane Converstion for Seaward Regal (GSI) Stove | Matt & Jessica's Sailing Page
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Old 06-03-2012, 17:34   #14
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Re: Converting CNG to LPG

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Been there done that. Here's a post I made showing at least the photos of my conversion.

CNG to Propane Converstion for Seaward Regal (GSI) Stove | Matt & Jessica's Sailing Page
EXCELLENT!!!...This is what I was looking for! I do not have a broiler, just a lower burner and 2 stove-top burners. I will try to contact the source you used for the Jets...Thanx.
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Old 06-03-2012, 19:14   #15
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Re: Converting CNG to LPG

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EXCELLENT!!!...This is what I was looking for! I do not have a broiler, just a lower burner and 2 stove-top burners. I will try to contact the source you used for the Jets...Thanx.
Happy to hear it helped. Let me know how it turns out
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