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Size NG/Propane line to 7.5JB: temporary


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  #1  
Old 10-28-2008, 08:16:23 PM
w peterson 54 w peterson 54 is offline
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Default Size NG/Propane line to 7.5JB: temporary

The line going into the gen. regulator is 3/4". Would I need to go that diameter from gen. to the fuel source or can I go down to 1/2 or even 3/8"?
I'm wanting to connect to run 'temporarily' for 15 mins or so as opposed to waiting until January for a permanent install at the cabin. I'm a little excited about getting this thing fired up.

Thanks in advance.
wep
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Old 10-28-2008, 09:06:30 PM
Gunny Gunny is offline
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Default Re: Size NG/Propane line to 7.5JB: temporary

How long is this line? Any bends? What pressure in this line? What size tank? What is the lowest temperature you can expect? All this figures in how this fuel system should be set up to work properly.

If I were setting up a LP vapor system, I'd use a 10 psi regulator at the tank, 1/2" copper to the genset, no tight or sharp bends if possible. Protect the line if there is any chance of it being physically damaged. At the genset, use another regulator to drop the 10 psi down to 2, then to 11" of WC, a solenoid valve a demand regulator and then to the mixer. Only unknown left would be the tank size. In this area a 90 gallon tank will work OK unless the temp drops below 20F, a rare event.

A lot of other ways to do it too.
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Old 10-28-2008, 09:12:53 PM
VaughnSimon VaughnSimon is offline
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Default Re: Size NG/Propane line to 7.5JB: temporary

Even 1/2" sounds a bit small for that size generator, but you failed to mention the length you need to go, which makes all the difference. Anyhow, if you can accept a big e-mail, I will send you the Onan LP gas bulletin that has a gas line sizing chart

Now here is what I did (dare I admit this?) :
For a one-time test, and to validate my choice of pipe sizes I went to the hardware store and bought some pipe-to-hose adapters, and connected my generator up through a dry length of garden hose. It worked great! Remember, you are only dealing with a few oz of pressure, and that garden hose is good for at least 100# of pressure.

Vaughn
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Old 10-28-2008, 09:17:55 PM
w peterson 54 w peterson 54 is offline
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Default Re: Size NG/Propane line to 7.5JB: temporary

Didn't make my plan as clear as I could have. I'd like to come off my home's natural gas line (presently 1/2") at the water heater and into the JB's solenoid valve & regulator.

wep
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Old 10-28-2008, 09:20:03 PM
w peterson 54 w peterson 54 is offline
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Default Re: Size NG/Propane line to 7.5JB: temporary

Guess I needed to add: my 'run' would be about 3-4 feet from 1/2" line to gen.

wep
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Old 10-28-2008, 11:35:28 PM
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EricWood EricWood is offline
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Default Re: Size NG/Propane line to 7.5JB: temporary

You should have a reducing regulator installed on your existing piping, after the meter somewhere, that feeds the gas into your house appliances.

Generators need to be plumbed in up-line of that. Your gas meter is likely being fed 2 psi, and that is what goes to your house's reducing regulator. You would want to have a tap in the line feeding towards the house, take that line towards your genset, then use a dedicated reducing regulator, that will take the 2 psi down to 11" WC. This is what would feed into the solenoid/KN demand regulator on your JB. As for pipe size, I'd go with the same size of pipe that comes from the meter, and stay with that size all the way to that 11" reducing reg.

For planning purposes, I use 120,000 btu for my JC (i'm sure its not near that in application, given my small house loads). I don't know if the JB would be half exactly; ie, 60,000, or just a little more. What else do you have running on gas? Furnace? Water heater?

All these appliances, and your generator, cannot exceed the capacity of your meter. Many meters usually have the max. btu's they will pass in the model number on the front--like A250, or A450 (number being the kbtu rating). If your numbers would add up close to max, have the gas company switch it out for you.

eric
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Old 10-29-2008, 09:41:33 AM
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Billy J Shafer Billy J Shafer is online now
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Default Re: Size NG/Propane line to 7.5JB: temporary

I would not tap in at the water heater or in the house. I have had more problems with this set up. The house can suck the fuel away from the genset. Have it tap in as Eric said and you will stop alot of problems. I had a back up unit at a hotel at DFW Airport. Would not run in the morning at lunch or at dinner. Strange problem and I thought the man was crazy when he told me this. Ran fine during the day. Used to run fine all the time . Testing found out they had installed larger stoves in the kitchen. During meal times gas would drop at the genset being sucked out by the stoves.
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Old 10-29-2008, 11:26:02 AM
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Dave Edmonds Dave Edmonds is offline
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Default Re: Size NG/Propane line to 7.5JB: temporary

If this is strictly a temporary setup, I would think that connecting the genny to the 1/2" gas line, and running it when the water heater is not heating, would give you some positive results. If the genny requires higher pressure than standard household gas pressure, the genny might not run very well under load, but it should run. For your permanent installation, follow the instructions above. There are some posts elsewhere on this forum that reference generators being on the same lines with other gas-burning devices (heaters, etc.), with bad operating results. You don't want your generator to stall when the water heater comes on!
Dave Edmonds
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Old 10-29-2008, 01:48:59 PM
w peterson 54 w peterson 54 is offline
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Default Re: Size NG/Propane line to 7.5JB: temporary

That was what I was wondering about - only for a temp 'run' for 10-15 mins or so to warm it up and possibly change oil.

wep
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