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 > Mh propane capacity discrepency

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down home

south

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Posted: 02/07/20 09:18pm Link  |  Quote  |  Print  |  Notify Moderator

Our 05 Revolution has a 38.4 gallon propane tank. The factory replaced the original tank circa 2008.
We let the tank run down to an indicated empty lat night.
Filled it this am but it would only take 24 gallons.
Last time a month ago or so the tank indicated it had 1/4 tank and it too 24 gallons.
Time before that it indicted 1/4tan or bit lower and it took 28. something gallons.
Clerk who filled it this am suggested letting it run out and opening petcock somewhere on the tank to let moisture out. I think he must have meant lube.
Neither seems reasonable, and...where is a petcock on a mh tank?

SDcampowneroperator

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Posted: 02/07/20 09:46pm Link  |  Quote  |  Print  |  Notify Moderator

Tank capacities are shown in gallons of water, theres a plate on the tank that shows that. Propane capacity is 80% of the water capacity (WC) #. A 38 gallon tank would hold 30.4 gal of propane. Never seen one that big.
Since you post you are taking on about 24 ga. , that is in the range of a 100# tank with a WC of 28. Check your numbers. That is a common size.
There is no air or water in a propane tank. The bleeder screw is a mechanical full level dip tube that will bleed liquid propane at the 80% level, vapor at lower levels. The guage on the tank is a mechanical float guage, that sends a signal to the in coach guage. Trust the on tank guage.
Also consider that if 80% is full, the 1/4, 1/2, 3/4 (full) should more properly read 1/3, 2/3 3/3 Full.

DFord

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Posted: 02/07/20 10:22pm Link  |  Quote  |  Print  |  Notify Moderator

There is no mechanical linkage between the float and the gauge. It's done with magnets. There's a lot of slop there. Don't expect to achieve a lot of repeatability. It's only designed to give you a rough estimate of the level of liquid propane left in your tank. When filled to 80%, your tank is full and you shouldn't put any more than that in it. If the gauge was completely mechanical, it would be venerable to leaking and that can't be tolerated because of the nature of propane.


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wildtoad

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Posted: 02/08/20 05:54am Link  |  Quote  |  Print  |  Notify Moderator

I doubt the gauges on the tank are precise. E may not be Empty. If you really want to know how much it actually holds, run it empty.


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wa8yxm

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Posted: 02/08/20 06:05am Link  |  Quote  |  Print  |  Notify Moderator

down home wrote:

Our 05 Revolution has a 38.4 gallon propane tank. The factory replaced the original tank circa 2008.
We let the tank run down to an indicated empty lat night.
Filled it this am but it would only take 24 gallons.


A full fill for a 38.4 gallon tank is about 27 gallons (34.8*80%) I'd say your 24 is very very close just a bit off on the float valve .


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winniman

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Posted: 02/08/20 06:35am Link  |  Quote  |  Print  |  Notify Moderator

My propane tank has a bleeder screw that the propane attendant opens when they fill the tank. It is located about 3/4 of the way up the tank on the front. It is at the 80 percent mark. When the propane reaches the bleeder valve, the propane will start to come out. At this point, the attendant closes the valve, and stops pumping propane. Since they are pumping liquid propane in, the valve allows air to be displaced by the liquid coming in. Im no expert, but I don't think ever tank has this same valve. I don't think my friends rv has one, but mine does. The reason you only fill the tank to 80 percent is that in hot conditions, the propane will expand. The 20 percent is a safety margin to allow for safe expansion.

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Posted: 02/08/20 06:44am Link  |  Quote  |  Print  |  Notify Moderator

The OP is using 1/4 etc, suggesting he is using the LP monitor on his range hood and not the actual gauge on the tank. As noted above, "full" and "half" are not the same on the two.

The lowest light on the monitor indicates from when it first turns to only that light and stays that way until all the LP is gone, so how much it takes to refill varies. Also ISTR that amount varies "as corrected" for temperature.


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dougrainer

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Posted: 02/08/20 06:50am Link  |  Quote  |  Print  |  Notify Moderator

DFord wrote:

There is no mechanical linkage between the float and the gauge. It's done with magnets. There's a lot of slop there. Don't expect to achieve a lot of repeatability. It's only designed to give you a rough estimate of the level of liquid propane left in your tank. When filled to 80%, your tank is full and you shouldn't put any more than that in it. If the gauge was completely mechanical, it would be venerable to leaking and that can't be tolerated because of the nature of propane.


Explain this. It is the standard Float Level unit for ASME tanks. It is what I have seen and repaired for 40 years. While it does use Magnets, it IS Mechanical. Doug

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dougrainer

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Posted: 02/08/20 06:57am Link  |  Quote  |  Print  |  Notify Moderator

On a correctly purged LP tank WHEN NEW, there should be NO AIR in any LP tank DOT or ASME after that. But, air can be introduced when the tank has been serviced or repaired. IF that happens you tell the LP station and they will PURGE the tank to get rid of any possible air. BUT, if a tank has never been "messed" with there is no real way to introduce AIR into the tank. The filling nozzles are connected and only then is LP liquid installed. The gauges are NOT that accurate. You can still have a few gallons even when the tank is showing empty. Doug

DFord

Near St Louis, MO

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Posted: 02/08/20 08:40am Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

Explain this. It is the standard Float Level unit for ASME tanks. It is what I have seen and repaired for 40 years. While it does use Magnets, it IS Mechanical. Doug

What I'm saying is there is no "direct mechanical linkage" between the float and the gauge needle itself. They are both attached to magnets separated by a layer of brass. Just as if you were to place magnet under a piece of glass and lay another on top, moving the bottom one will cause the top one to move. The movement will not be completely smooth all the time. It moves in spurts only when the pull of the lower magnet overcomes the drag is overcome of the one on top of the glass. It's not as if the float was directly directly turning the same shaft the gauge needle is connected to - they are separated by a layer of brass machined under the gauge dial in threaded plug housing which makes the gauge leak proof.



When the tank is being filled and the purge valve is open - that's not "air" that's being purged, it's propane in its gaseous form. All the appliances use propane in this form. The liquid propane is boiled off before it leaves the tank.

You can use this pressure - temperature chart to see the pressure in the tank at various pressures in the tank and viceversa: HC-290 (PROPANE) PRESSURE - TEMPERATURE CHART

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