woodspliter
Just taking over my first liquid cool gen maintenance and the customer says it has always shown low fuel pressure when running and sometimes does not start.  On site inspections indicates the fuel line is to small and the regulator may be also.  It is a V8 Ford engine, Generac model QT04854ANAX serial 7257697.  The fuel line is 3/8 inch copper and runs about 70 feet underground from tank.  I do not install the gas hook up on the units I install but the charts I find online seem to indicate that it my need a line 1 1/4 inch black pipe.  Do you guys know it that is correct?  What other piping is available to use?  I would like to have my ducks in a row when I contact a gas supplier or gas installer to fix the problem.  The house also has a gas hot water on demand heater on the same line.
Does 163,200 BTU per hour sound right at full load.  Gas line of 1 1/4 inch black. Just getting started at gathering information.  Sloppiest gas install I have ever seen.
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DougO
Since you indicate " underground tank " sounds like LPV fueled. More information is needed on the fuel suppy such as static pressure, running pressure ect i have two of these that i work on and maintain. But they are both NG.
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78buckshot
The normal set-up for the house would be a primary regulator at the tank to reduce tank pressure down to 10 psi, then 3/8" copper to the secondary regulator to reduce down to 12.5" w.c., then into black pipe into the house. The black pipe would be sized according to the maximum load by adding all of the BTU's of the gas appliances. When a generator is added to the gas system it should have a dedicated primary line tee'd off of the 3/8" near the tank, then run close to the generator and set a secondary regulator for the size of the load needed for the maximum BTU of the generator, then the correct black pipe into the generator. In your case 1/2" copper for the primary wouldn't be a bad idea but the 3/8 can handle a lot because of the 10 psi primary pressure. You can adjust both regulators to meet pressures needed but I bet the single secondary regulator can't supply the volume needed for the house and generator combined.
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Birken Vogt
Secondary regulator needs to be 5 feet from source of ignition (generator set) so we typically pipe them with fat pipe all the way back.  That or set a pair of risers at the proper setback from the generator, or build a tripping hazard of aboveground pipe to a regulator properly set back.
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woodspliter
Buckshot, I guess I was not very clear on the gasinstallation of the  Generac 48kw QT04854ANAX serial 7257697., it is LPV fuel,3/8 inch copper line runs to the primary fuel regulator near the generator only . The house is on a different line . The  line comes out of the ground right at the  generator base, sets the regulator, unions ,couplings , trap etc. and then it has a curled up grey pipe of about 4 feet in length into the demand regulator of the generator.  Another company has been serving it and never solved problem of low fuel pressure when running.  I doubt it will handle much load but have not tried it yet.  I was just concerned that the small copper line can feed the engine at all.  I am looking into the fuel regulator today to see what size it is for gas flow.  Does the piping from the primary regulator to the demand regulator form sort of a reservoir of fuel when running. Starting to suspect the primary regulator will flow enough inches when running. Does 163,000 BTU sound about right for a 48kw. full load supply.  Oh the regulator looks like the same size I see on most of the 22kw air cooled units.
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Birken Vogt
3/8 copper 70 feet at high pressure 180 kBTU.  Quick check says generator about 756 kBTU at full load.  No way 3/8 tube can support this unit, needs to be 1/2 pipe minimum at high pressure, or we would probably have done it at 1.25" pipe at low pressure to keep the regulator away.
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78buckshot
According to the LP Servicemans Handbook you should use 5/8" soft copper if the run is 70 ft between the primary and secondary regs. I have not seen any LP installations where there is not a primary regulator on the tank so I am assuming that is the set-up on your unit. Now with an underground tank I am not sure where the primary would be, maybe they are running full tank pressure in the 3/8" line to a 2-stage regulator(primary and secondary combined in one regulator). In any case you need to supply that generator with 660,000 - 760,000 BTU/hour at 11.5" - 13.0"w.c. full load. The piping from the secondary reg. to the generator should be 1.25" black or equivalent. I have had good success setting the secondary at 13.5" static pressure and if all of the other piping and regulators are sized correctly and responding correctly you should see no more than 1" pressure drop from static to running mode.
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Birken Vogt
You can't run tank pressure anywhere because liquid will recondense in the line.  Usually 10 psi, some places where it gets extremely cold use 5 psi to avoid recondensation at 10 psi if it is that cold.
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78buckshot
Right you are Birken Vogt!, if woodsplitter can describe the set-up we can help diag the low fuel pressure issue.
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