gas supply line size

Old 02-24-03, 08:42 PM
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gas supply line size

I am installing a 12kw natural gas backup generator. I already have an unused 1/2" gas line outside the house where the generator will be installed. The gas inlet on the generator is 3/4". The fuel consumption of the generator is 114cu.ft./hr. at 1/2 load and 185 cu.ft./hr. at full load. Will my 1/2" line supply enough gas or do I have to replace it with a 3/4" line. Thanks for any input.
Old 02-25-03, 05:22 AM
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Hello: Cory

If the inlet gas line to the generator is 3/4 inch, that pipe diameter must be maintained all the way back to the gas supply source.

The 3/4 inch diameter is the minimum size if the generator isn't too far from the gas source. As the distance between the two increases, so must the pipe diameter to maintain the proper gas volume to supply the engine.

Failure to supply the required volume of gas will cause the engine to run too lean, create starting problems and acceleration problems if the engine does not run at a constant speed.

By constant engine speed I mean some generators reduce engine speed to an idle when no load is placed on them. Generator engine also have governors which maintain the set speed and need additional fuel when a load is place on them.

A resrticted gas supply caused by a pipe too small to carry the fuel volume will cause the engine to bog down, hesitate or stall under load demands, etc.

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Old 02-25-03, 05:27 AM
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I will tell you how to figure this yourself.

You need to know the line pressure and the total length of pipe run along with all other appliances attached to the line and their BTU input. Make a line diagram showing this info for your referrance.

Go to a local library and get any copy of the Uniform Plumbing Code. Look at the gas sizing charts.
You can also use the National Fuel Gas Code, same charts and info.

You will see why you need the above info when you locate the gas charts.

More questions, ask away and someone will help you.

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