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Generac Air Cooled Generators Troubleshooting Questions, Answers, and Information About Air Cooled Guardian Generators

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Old March 28th, 2007   #1
Pakal
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Default Propane tank

Hi there, I do not have natural gas supply where I live , I could only connect a 100 lb Propane gas round tank to the generator. What gas regulator do I need to use between the tank and the generator ?
Pakal
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Old June 23rd, 2007   #2
Pakal
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Default Propane tank

Hi again Kelly, I never got an answer to my question. Would a simple regulator, like the one I use to supply my stove, be OK for the generator. Furthermore the GPL tank will only supply the generator . How long would it last (100 lb) if connected to a 7kw or a 10kw guardian ?
Thanks for your time,

Pasquale
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Old June 23rd, 2007   #3
Kelly Myers
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Hi Pakal, sorry for overlooking your question!

1st off, I'm NO fuel expert, I'm just an electrician. What we have experienced with 100 lb tanks, is they freeze up! I'm sitting on my deck, so I don't have my stat sheets, but the 7/10kw should be around a gallon/hour @ 50% load. I will correct this number on monday. I'm not sure how a pound resolves to gallons. I really wish someone who knows fuel could start posting here! I might have to find somebody to help out!

I'm not sure if the normal household regulator will work, because I believe you normally need two. One to drop pressure, and one to adjust W.C.
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Old June 23rd, 2007   #4
cosmicvoid
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I'm not a fuel expert, either, but recently I did a lot of research on regulators and gas flow. You do need two stages of regulation for LPG. The first stage (red housing) drops the tank pressure (25~200 psi) down to 10 psi, the second stage (green housing) drops the 10 psi down to 11"wc. It is common to see integral 2 stage regulators that combine both into one gray housing.

Here is a pdf catalog from a valve company, but in the middle section, about pages 71~87, there is a large amount of really useful info about how the valves/regulators work, and tables for gas flow, pipe sizing, etc. It will probably answer many of your questions. There is a 'rule of thumb' chart for gas flow vs temperature and tank shape (surface area of liquid propane), and a lot of discussion about 100 lb DOT cylinders, and freeze-up.

http://www.sherwoodvalve.com/pdf/lpg.pdf

Hope this helps.

Last edited by cosmicvoid; June 23rd, 2007 at 10:25 PM..
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Old June 26th, 2007   #5
irq3
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Take a look at this webpage:
http://www.propane-generators.com/lp_gas.htm

(Rules of thumb)
*It requires 2 horsepower to produce 1000 watts of energy per hour

*Under load, each horsepower consumes 10,000 BTU per hour

*LP Gas contains 92,000 BTU per gallon

The regulator size you need depends on the size of the generator (they are rated in BTU's/ HR).

For example: a 4,000 watt generator = 8 HP engine X 10,000 BTU/HR = 80,000 BTU/HR (full load). The example would need a regulator capable of handling 80,000 BTU/ HR capacity.

Pay special attention the "Vaporization Rates of Cylinders" (at 25% full) chart too. Depending on the size of the generator, if you live in a colder climate, the 100# cylinder may be too small (and freeze up).

As for needing a two stage regulator, it also depends on the BTU/HR load, distance to the propane tank, and the size of the gas line. You may be able to use a single stage regulator (11-14" WC).

This site also has a hook up hose sizing chart:
http://www.propane-generators.com/hook-up_hoses.htm

Remember, the NFPA gas code requires a propane tank to be at least 10 feet away from a combustible source (generator, etc.). Also, use a rubber flexible hose to connect the generator (vibration)!

Your best bet may be to lease a 420# tank and regulator from a gas company, have them install and fill it as needed. Usually, you get a better price on propane when buying in bulk or pre-buy.
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