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Propane question - Generator Fuel

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Forum topic by Marleywoodie posted 06-04-2020 08:06 PM 355 views 0 times favorited 8 replies Add to Favorites Watch
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Marleywoodie

45 posts in 1231 days


06-04-2020 08:06 PM

It’s germane to the forum, because I use the generator when we lose power in the shop. LOL.

I’ve got three 120g propane tanks to run my generator. They are “ganged” together, but it only seems to draw from the first tank in the line. It would seem to me that they would equalize, but the other two are full up when the first is down @ 30%. Is this correct/normal?

Thanks

-- - Not all who wander are lost -


8 replies so far

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CaptainKlutz

3327 posts in 2296 days


#1 posted 06-04-2020 09:10 PM

Generally small propane tanks release propane as saturated gas via vaporization of liquid, not by dispensing the liquid directly. Since the equalization is done with saturated vapor, the other tanks will never transfer liquid between each other. They only supply propane vapor generated by the exposed liquid surface, with pressure determined by gas law physics.
If you wanted to move liquid between tanks, would have to invert the tank, so that liquid was forced out the gas vent. But this only works when one tank has lower pressure than other. As soon as the pressure is same the transfer stops.

Hope this makes sense.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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Marleywoodie

45 posts in 1231 days


#2 posted 06-04-2020 09:14 PM



Generally small propane tanks release propane as saturated gas via vaporization of liquid, not by dispensing the liquid directly. Since the equalization is done with saturated vapor, the other tanks will never transfer liquid between each other. They only supply propane vapor generated by the exposed liquid surface, with pressure determined by gas law physics.
If you wanted to move liquid between tanks, would have to invert the tank, so that liquid was forced out the gas vent. But this only works when one tank has lower pressure than other. As soon as the pressure is same the transfer stops.

Hope this makes sense.

- CaptainKlutz

It makes sense, but what are the practical consequences of this in my system? Does Tank A go to near empty and Tank B provides vapor into Tank A to run the generator? This is the part I don’t understand.

-- - Not all who wander are lost -

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Sparks500

277 posts in 1132 days


#3 posted 06-04-2020 09:16 PM

Well, I sell propane and propane accessories…..

-- A good day is any day that you're alive....

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Lazyman

5634 posts in 2189 days


#4 posted 06-04-2020 09:33 PM

Are you sure that the other tanks aren’t shut off?

Perhaps it has some sort auto changeover valve? I seem to recall that some RVs that have two tanks have a valve that will automatically switch over to the second tank when the first one gets low. This allows you to be able to take the empty to get it refilled and always have a full tank instead of 2 empties. Probably not really the same thing as a 160g tanks but maybe they have a similar regulator?

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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CaptainKlutz

3327 posts in 2296 days


#5 posted 06-04-2020 09:48 PM

It makes sense, but what are the practical consequences of this in my system? Does Tank A go to near empty and Tank B provides vapor into Tank A to run the generator? This is the part I don t understand.
- Marleywoodie
The pressure is defined by surface area of liquid and temperature. When the 1st tank has reduced surface area, the pressure drops and the full tank with larger surface area and higher pressure delivers the gas.

Perhaps it has some sort auto changeover valve?
- Lazyman

That would my guess too.
Typically when ganging tanks you are supposed to use regulator that includes auto change over.
They don’t open the valve to tank until the pressure from first tank drops to low.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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Marleywoodie

45 posts in 1231 days


#6 posted 06-05-2020 12:35 AM



Well, I sell propane and propane accessories…..

- Sparks500

Aren’t you special? How about helping?

-- - Not all who wander are lost -

View Kazooman's profile

Kazooman

1514 posts in 2754 days


#7 posted 06-05-2020 12:23 PM

The pressure is defined by surface area of liquid and temperature. When the 1st tank has reduced surface area, the pressure drops and the full tank with larger surface area and higher pressure delivers the gas.

- CaptainKlutz

The pressure is determined by the temperature of the system. The surface area determines the rate that the vaporization of the liquid can keep up with demand. The volume of liquid in the tank determines how much the heat of vaporization affects the temperature. If the surface area determined pressure then the pressure in a tank at equilibrium would depend on orientation.

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Foghorn

526 posts in 188 days


#8 posted 06-05-2020 04:04 PM

Are the tanks manifolded together and using a single first stage regulator or is there a regulator on each tank? If a single regulator, they should all go down at roughly the same rate depending on the sun/shade etc. If there is a separate regulator on each tank, they would have to be balanced very close to get a similar draw down rate for all tanks.

-- Darrel

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