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Propane vapor or Liquid draw??


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  #1  
Old 12-12-2007, 09:12 PM
Bob E Bob E is offline
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Default Propane vapor or Liquid draw??

I'm learning about vapor engines, especially Onan LPG, since I have 3 gensets that run on Propane. I understand that the usual forklift application draws the liquid from the tank and a vaporizer somewhere in the system before it gets to the carburetor. Is this correct? What is the advantage of the liquid draw? Is it the bottle position that most forklifts use or what? I know I've had trouble with freeze ups on forklifts. Looks like vapor draw would be better. I've decided I need a larger "tank regulator" and larger tank than the 20# I've been using, without load.

Bob E
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Old 12-12-2007, 10:02 PM
Jim Rankin Jim Rankin is offline
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Default Re: Propane vapor or Liquid draw??

Bob,
A tank should not freeze up if it is feeding liquid. Feeding vapor is what refrigerates the tank. LPG liquid is just like freon in an AC or heatpump, when it changes from a liquid to a vapor, it absorbs heat, a lot of heat. This has to be supplied by something, outside air on the surface of a large storage tank, engine coolant in a "vaporizer" type regulator, or hot air off an air cooled engine over a special vaporizer designed for that application.

Which is best depends on what the rate of draw is, the size of the storage tank desired, the lowest outdoor temperature the tank will be operated in.

Cheapest way may be to use an existing large storage tank and feed vapor, if you already have the storage tank or want to have a lot of reserve for prolonged emergency use.

If you want a smaller tank, perhaps with some portability, even though your generator draws quite a bit of gas, you might rather have a forklift size tank setup with liquid draw.

If the demand is very low and you can keep the tanks in a fairly warm outdoor environment, you can perhaps use grill bottles and feed vapor.

There is sometimes a small problem upon startup in very cold conditions feeding liquid. The LPG is refrigerating coolant that is already almost cold enough to freeze. Some vehicle systems have a valve you can open to allow vapor draw until the engine has warmed up and then it is supposed to be closed again. If this valve is inadvertantly left open and the engine is worked hard, the tank will frost up and starve the engine.
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Old 12-13-2007, 09:59 AM
K D Redd K D Redd is offline
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Default Re: Propane vapor or Liquid draw??

Jim cover most of you question well. I have had two experiances of the vaporizer/demand regulator on an LPG fuel vehical "Freeze Up" . In both cases the vaporizers were heated by the liquid coolant of the engine and the coolant level was low. With the coolant level low the coolant was not circulating through the vaporizer. One happened to Dad on the CO1800 International we use during Fescue season. The other happened two weeks ago on a former LP transport truck that has been converted to a turkey litter spreader.

Kent
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Old 12-13-2007, 10:05 AM
Jim Rankin Jim Rankin is offline
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Default Re: Propane vapor or Liquid draw??

The old "Low coolant safety system"
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Old 12-13-2007, 01:04 PM
Bob E Bob E is offline
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Red face Re: Propane vapor or Liquid draw??

Thanks guys, I have the demand regulator and solenoid valve. I am going to up grade the high and low pressure regulators to get a better volume flow under load. In my haste to get some power, I didn't have the demand reg. in the required vertical position. I should have been ready before the lights went out.

Bob
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Old 12-13-2007, 06:51 PM
Ed Radtke Ed Radtke is offline
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Default Re: Propane vapor or Liquid draw??

My 4 cyl. Kohler flathead does just fine on vapor in warm and cold weather.Demand reg. is from a small briggs and feeds about a 3/4-7/8 clinton carb.It starts instantly using the primer button on the reg.
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