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Converting a torch from Natural Gas to LPG


#1

Hi there

I am lusting after a proper hearth and have found a nice second hand
Flamefast natural gas / air hearth with two torches. However my
workshop is kitted out with LPG, not natural gas.

I spoke with Flamefast and they will rework the torches to make them
function with LPG, but that will cost me UKP 45 a torch.

I don’t suppose anyone in the wide world of Orchid could tell me what
this process involves and whether there is a fix I could undertake
myself? If it is a matter of altering an aperture diameter then my
trusty Foredom and a pin vice are surely up to the job? Or, is
messing with kit that deals with compressed, flammable gasses best
left to (pricey) professionals?

As always, your help is much appreciated.
CP
Chris Penner
Collarsandcuffs.co.uk


#2

Hello Chris, There is no need to make this change complicated; it
isn’t. Set up your torch and switch tips until you are happy. I work
with natural gas at my store and propane at home. Torches have been
moved back and forth more than once.

Tom Arnold


#3

Hi Chris,

I had this happen to me about ten years ago. I bought a second mouth
blown Flamefast torch secondhand that was set up for natural gas and
had them convert it to LPG, it cost me about 35 then.

As I understand it the hole size that the gas comes out of needs to
be adjusted, mine was hard to get at and it was a very small hole,
with a hearth torch it should be easier, what you need to do is see
if it is easy to get at and if you can find out the comparative heat
output for the two gases, I suspect it will not have to be perfect,
it might just be a case of soldering in a bit of tube and then
gradually drilling it out until you get it right. You could always
have one done and then you will know the right size:), or ask if
anyone else has got one and get them to measure it.

I use a Sievert for bigger jobs and casting, as the nozzles go up in
size the orifice gets bigger, if you like I will measure a couple, it
just depends how big a thing you want to heat.

Regards Tim Blades.


#4

Have you tried them without modifying them yet? LP and natural gas
aren’t that dissimilar I don’t believe (I could be wrong), except
that natural gas from the gas company is generally delivered at a
lower pressure than what is used for LP, at least on this side of
the pond. I know when converting torches to or from acetylene / LP,
it requires different needle valves and seats in the knobs as well as
different orifices in the tips, something to do with the molecular
size of the gas. I used to have a couple of old acetylene torches
that I used with LP. I also use an old acetylene regulator on my
casting torch that runs on LP. It’s not supposed to work, but it
seems nobody bothered to tell the torches. I run flame arrestors on
each and every torch I use, and highly recommend their use. Safety
first!

Dave


#5
Have you tried them without modifying them yet? LP and natural gas
aren't that dissimilar I don't believe (I could be wrong), except
that natural gas from the gas company is generally delivered at a
lower pressure than what is used for LP, at least on this side of
the pond. 

Actually they are quite different. Natural gas is mostly methane CH4
while propane is C3H8 but what you get from a fuel supplier is a mix
of propane and butane.

Natural gas is about 1/2 the heat output per volume unit that
propane does and you need over twice the oxygen per propane molecule
to burn it as compared to natural gas.

CH4 + 2 O2 > CO2 + 2 H2O + heat
C3H8 + 5 O2 > 3 CO2 + 4 H2O + heat

What doe all that mean? If you have a naturally aspirated torch
where the combustion oxygen is drawn in though a venturi type mixer
like a prestolite or bernzomatic torch then it likely will not even
come close to working. If you have a torch with two hoses one for
fuel and one for the oxidizer source whether it is oxygen or
compressed air and it is controlled by opening and adjusting valves
on the torch handpiece then there are no orifices involved in fuel
metering and the torch will typically work but it may be less
efficient at producing heat. That will vary a lot depending on the
tip design. Anyway as a user unless you do direct comparison tests
you will may not notice a difference.

I know when converting torches to or from acetylene / LP, it
requires different needle valves and seats in the knobs as well as
different orifices in the tips, something to do with the molecular
size of the gas. I used to have a couple of old acetylene torches
that I used with LP. I also use an old acetylene regulator on my
casting torch that runs on LP. It's not supposed to work, but it
seems nobody bothered to tell the torches. I run flame arrestors
on each and every torch I use, and highly recommend their use.
Safety first! 

The difference between acetylene and propane is very different first
from a safety perspective the hoses used with acetylene are attacked
by propane and can cause a catastrophic failure or simply just crack
and leak. In either case not a good thing. So make sure you are
using propane rated hoses. Another big difference is acetylene needs
1/5 the oxygen per molecule that propane does to burn so you need
very different amounts of oxygen. Also a propane molecule is much
larger than an acetylene one so very small tips like the smallest
ones on the little torch just will not work with propane as you just
can’t get enough gas through it fast enough to create a stable flame.

James Binnion
James Binnion Metal Arts