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Minneapolis Moline Tractors Discussion Forum
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how lp fuel systems operate

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EIL

10-21-2003 07:59:51




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Hello. I am currently going to a vo-tech school to be a diesel mechanic and no matter how hard I look through all the tons and tons for books we have, I can't seem to find a book or something that will explain how an lp (propane? or butane?) fuel system operates. I totally understand how gasoline and diesel engines operate but have no clue on lp. Someone in the past had brought in a five star lp and it has interested me ever since. Then the same farmer brought in an allis chalmer lp and it made me even more curious. I did post this same question in the general tractor discussion board a few months back but nobody replied so for heavens sake, can someone please explain it to me. Come this May I will either be working at the local john deere dealership or the local case/kubota/mahindra dealership. I am dieing to know how these fuel systems work. Also, does a karosene fuel system opperate in the same way as lp? Oh, one last question, what is the difference between butane and propane. God bless anyone who will explain any of this to me. Thanks for any help anyone can give me!!!!! !

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EIL

10-22-2003 02:01:40




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 Re: how lp fuel systems operate in reply to EIL, 10-21-2003 07:59:51  
Thank you all very much. For some reason when I ask about lp nobody ever has a really good explanation, I'll know next time to just come and ask hear. Thanks for getting me to understand this stuff. I really appreciate it!!!!! !!



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Roger

10-21-2003 22:54:03




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 Re: how lp fuel systems operate in reply to EIL, 10-21-2003 07:59:51  
If you are really interested in working on LP eq.
find a good LP dealer that can get you into the
Impco Carberation school You will learn more in 3
days at this school than you can imagine. Some of
the basics are - Modern LP Eq. works off a demand
system. The motor tells the carberation how much
fuel to send it. Older systems used a balance
system. The Vaporizer & Carb decided how much fuel
the motor needed. Never mix pressures. The new eq.
works off 4 to 5 lbs. pressure. Some systems like
Zenith or All Gas work on 5 to 6 lbs. pressure.
Repair kits come with instructions and if followed
will usualy fix your problem. A lot of problems
are blamed on LP Gas. One of the most common is
4020 John Deere. They will start fine when cold,
but when shut off at noon they won't start. The
problem is the original ignition switch. It had a
voltage reducer built in. It would crack with age.
When the ignition switch was hot from hours of
working in the field, the porcilen would expand
and the switch would short out to the dash,
causing lower voltage. The tractor would run, but
when shut off it would not have the extra voltage
needed to start an engine. There are hundreds of
things like this that can only be learned with
years of experiance. A lot of people will tell you
that LP is too much trouble. These are the people
that don't want to learn. As for the comment on LP
being a dirty fuel. Get a different LP dealer. We
deliver fuel to a plant that has 80 fork lifts
that average 8,250 hours per year, almost 23 hours
a day running time. They get new forklifts every 2
years. A lot of times we never replace a fuel
filter on any of them.

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moline

10-21-2003 19:42:19




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 Re: how lp fuel systems operate in reply to EIL, 10-21-2003 07:59:51  
EIL,I will give this a try,guys correct me if Im wrong.There are 4 basic parts to a lp system.Tank,filter,regulator(sometimes called a vaporizer)and carb.When the vapor valve is open,vapor is picked up from the top of the tank and flows through the filter to the regulator.The regulator has a diaphram in it,usually controlled by engine vacuum.The diaphram is connected to a needle valve which only allows a small amount of fuel through it which lowers or regulates the amount and pressure of the fuel.This regulated amount goes to the carb for mixing with air for combustion.When the liquid valve is open,liquid propane flows through the filter to the regulator.The engine coolant flowing through the back of the regulator heats the liqid propane causing it to vaporize(hence the name vaporizer).The vaporized fuel is then regulated to the carb as I explained before.As the other gentlemen pointed out,LP is higher octane and runs better on a higher compression than normal gasoline.Kerosene likes lower compression than gas and requires good cylinder head and manifold heat to burn efficiently.Kerosene uses a carb like a gasoline engine.There are tuning and engine modifications(just like gas and diesel)that make a propane engine run better.I hope I helped a little as I am by no means an expert,I just like propane engine better than gas or diesel.

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Mark H.

10-21-2003 14:37:25




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 Re: how lp fuel systems operate in reply to EIL, 10-21-2003 07:59:51  
EIL, I'll give this a shot, LP gas is stored under pressure in the fuel tank .From the tank the gas goes though a filter to a convertor(when it turns from a liquid to a gas the convertor will freeze this is why cooling hoses from the cooling system go to the convertor to keep it warm) where it goes from a liquid to a gas then to the carb to the engine.This is a very clean burning gas and I believe it's a higher octane I've seen lp put into the air inlet on some forklifts and they run fine. Some engines can be a two gas set up with lp/gas as the fuels. Most tractors start on vabor the switch to liquid. I hope I helped you some. It's a very simple setup Mark H.

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dlp

10-22-2003 18:43:53




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 Re: Re: how lp fuel systems operate in reply to Mark H., 10-21-2003 14:37:25  
The filter is usually seperate from the converter & is called a lock-off. The lock-off houses the filter & a shut-off that is opened by (usually) vacuum. A lot of newer styles are going to a one piece unit.



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Dave B.

10-21-2003 18:57:47




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 Re: Re: how lp fuel systems operate in reply to Mark H., 10-21-2003 14:37:25  
EIL, I'm a lurker here, but I have 9 LP-powered forklifts in the plant where I work. Mark was essentially correct - LP (liquid petroleum) gas is stored under pressure and is converted to gas and burned in the engine like any other petroleum fuel. However, it needs a spark to ignite, unlike a diesel. Butane (C4H10)is a "heavier" gas than propane (C3H8), meaning that it has more of the carbon-hydrogen atoms and thus more energy per pound than propane. Propane does have a higher octane rating. The cool thing about propane-powered engines is that they run very clean; there is very little wear of the cylinder areas as there is no liquid fuel to "wash" the cylinder wall, and no liquid fuel getting into the crankcase via blowby the rings. Valves stay very clean as well. The only drawback we've seen is that propane can be a very "dirty" fuel - lots of particulates, so that a filter is necessary to keep the small orifices in the "carb" from being plugged.
Hope this hasn't bored you to death. Good luck in your endeavors - we need more guys like you.

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