OK I am officially confused.I took one of my 40lb. propane cylinders out of my new RV to have it filled. A note on the door of the propane compartment said do not fill over 80%, could cause fire,explosion etc.I told the guy that was filing the bottle to fill to 80%, he didn't know what I was talking about and since I didn't know what I was talking about we filled it to 65 total lbs where his info showed it full at 75 lbs.Anyhow since this is a safety issue can anyone help me out. since this is a 10 gallon tank am I only supposed to put 8 gallons in it?I have always taken them to the guy, he puts it non a scale and fills it to the total weight on his chart. Is this 80% or is it over filled?For those of you that want me to do a search, I did and got 503 pages and although I am retired I don't have enough time to read all of the info.

80% is the normal fill quota. Mine are by volume, and I know little about weight.As for searching, your comment reminds me of a gal who won't use google because she can't read 1,108,455 responses.

Modern propane tanks are considered full at 80%, to allow expansion room. They fill with liquid propane, which turns into a gas that will flow to your burners and such. Modern tanks have a internal shut-off to prevent over filling. On non-portable tanks, an overflow vent valve is opened, and then the tank is filled until liquid propane comes out or the valve shuts off, at 80% full.

I have been told, so I can not state with authority, that each gallon of liquid will result in about 65 gallons of gas. Anyone else know the exact value??

Tank has an OPD valve to prevent over fill. Tank is already designed to stop at 80%. No need to short fill to 80% of 80%.100% filled to capacity (40 lbs.) is 80%.

Depending on the age of the tank there are two over fill indicators that go off at 80%Modern tanks have a float type valve. at 80% it closes and filling ceases. HARD.Older and modern tanks have a "Visual Overfill indicator Valve" Yes that is the name of the valve.Many people, will tell you you need to open this valve to let the air out of the tank becaus you can not compress air... I have no idea where thy went to school but...Well.. I will forgoe some serious insults (1 Air is easily compressed.. I mean what is filling your tires and 2: No air IN the tank aftr the first (PROPER) filling,,,only propane liquid and gas and some contaminats).When that valve starts spitting liquid (Comes out as a white cloud,like 40 degrees below white cloud)the tank is 80% full.

Propane fill question | Good Sam Community

RinconVTR
Explorer
Mar 29, 2015
RJsfishin wrote:
red31 wrote:
RinconVTR wrote:

Go ahead and fill an LP tank 100%, it will not be functional for long due to lack of pressure.

Baloney.

-----------------------------------------------------------------
Bull is right !
If ya don't have the foggiest idea what yur talking about, its much better to just stay out of it all, and not look so stupid.

EDIT. Post modified. Nothing wrong with the original, but its not worth continuing here. People don't post anything to back their stance, they just attack.

LP does "boil" and expand in a sense when you open the valve, so my thinking may indeed be wrong. Not entirely, but its hard to prove over the internet otherwise.

But if you are going to call someone out this way, at least state some sort of reasoning and not just call names.
time2roll
Nomad
Mar 29, 2015
RJsfishin wrote:
red31 wrote:
RinconVTR wrote:
Go ahead and fill an LP tank 100%, it will not be functional for long due to lack of pressure.
Baloney.

-----------------------------------------------------------------
Bull is right !
If ya don't have the foggiest idea what yur talking about, its much better to just stay out of it all, and not look so stupid.
Easy there guys. Everyone knows that is why you need a dual tank system and crossover regulator. The second bottle is to keep the first bottle pressurized. ;)
RJsfishin
Explorer
Mar 29, 2015
red31 wrote:
RinconVTR wrote:

Go ahead and fill an LP tank 100%, it will not be functional for long due to lack of pressure.

Baloney.

-----------------------------------------------------------------
Bull is right !
If ya don't have the foggiest idea what yur talking about, its much better to just stay out of it all, and not look so stupid.
hotpepperkid
Explorer
Mar 28, 2015
If it as 40 lb tank put it on a scale and put 40 lbs of propane in it, wheather that is 80% 90% or 100% it doesn't matter
hotpepperkid
Explorer
Mar 28, 2015
If it as 40 lb tank put it on a scale and put 40 lbs of propane in it, wheather that is 80% 90% or 100% it doesn't matter
red31
Explorer
Mar 28, 2015
RinconVTR wrote:

Go ahead and fill an LP tank 100%, it will not be functional for long due to lack of pressure.

Baloney.
RinconVTR
Explorer
Mar 28, 2015
wnjj wrote:

The reason for not filling the garden sprayer to 100% is a functionality one. The reason for not filling the LP to 100% is a safety one. They operate on completely different principles.

No sir. They are the actually pretty similar in principle.

Go ahead and fill an LP tank 100%, it will not be functional for long due to lack of pressure. Liquid...it doesn't compress, remember? And LP will not remain a liquid, unless its under pressure. It requires a volume of "air"...under high pressure...for the tank to function.

SO that 20% is not just there for thermal expansion (safety), its there for pressurization as well. Just like the garden sprayer.

And that 20% is not a magic number, it can be much lower for these tanks to operate, don't get me wrong. The expansion rate of LP is very high. The US has very strict, protective rules, as we all know.
wnjj
Explorer II
Mar 27, 2015
RinconVTR wrote:
wnjj wrote:
RinconVTR wrote:
sato4000 wrote:
My RV dealer said he will fill up the propane 100 percent if you want.

Impossible.

For perspective...take a pressurized garden sprayer. Fill it to the brim, 100% filled. Then try to add air pressure and spray. You might get a drip of water, if your lucky.

Same principle here with LP tanks, but there are yet more reasons as to why 80% max fill is standard, and already mentioned.

The garden sprayer works nothing like your LP tank. With the garden sprayer, you need air that is compressible to store the pressure needed to push water out the hose.

LP boils at -44F so it wants to convert to gas and flow out of the hose, all by itself. There's no pressurized air helping to move the LP along.

The 80% is for thermal expansion.

I was hoping that when I started my post with "For perspective...", using the reference as only a crude example to help others understand 80% fill issue...would not be taken as a claim that pressurized water tanks are the very same as LP tank.

I didn't take it as a claim that the two are the same, only the claim that they worked the same. You used the words "same principle". That means the same theory of operation. I simply pointed out that a garden sprayer operates NOTHING LIKE an LP system. There's no more point is suggesting that overfilling a garden sprayer is "perspective" for an LP cylinder than overfilling a wheelbarrow is. The only thing they share is that both are some kind of liquid in some kind of container.

The reason for not filling the garden sprayer to 100% is a functionality one. The reason for not filling the LP to 100% is a safety one. They operate on completely different principles.
dougrainer
Nomad
Mar 27, 2015
red31 wrote:
An overfilling prevention device must not be the primary means to determine when a cylinder is filled to the
maximum allowable filling limit.
NFPA 58, §7.4.4.1

Overfilling Prevention Device [“OPD,” “stop valve”]. A safety device that is designed to automatically prevent a
container from being filled beyond its maximum permitted filling limit.
NFPA 58, §3.3.49

Fixed Maximum Liquid Level Gauge [“outage gauge,” “spitter valve,” “spew gauge”]. A fixed liquid level gauge that
indicates when the liquid level in a container has reached its maximum permitted filling limit.
NFPA 58, §3.3.29.2

The formula for filling LP-gas containers by weight is as follows:
(1) Determine the propane capacity in pounds by multiplying the total water capacity in pounds by 0.42.
(2) Add the tare weight of the cylinder to the liquid weight of the product plus the weight of the hose and
nozzle. The total weight of these three is the proper scale setting.
LP-Gas Safety Rules, §9.136(a) (TEXAS)

This is correct, but Texas is one of the few states that has a comprehensive system and laws/rules for LP. A LOT of states is fly by the seat of your pants. ANY IDIOT is allowed to fill and service LP systems and containers, which is too bad. Doug
NinerBikes
Explorer
Mar 27, 2015
AllegroD wrote:
smkettner wrote:
Tank has an OPD valve to prevent over fill. Tank is already designed to stop at 80%. No need to short fill to 80% of 80%.

100% filled to capacity (40 lbs.) is 80%.

Considering the age of your rig, the above should be the answer.

12th Man Fan wrote:
For those of you that want me to do a search, I did and got 503 pages and although I am retired I don't have enough time to read all of the info.

So your answer to the many hundreds of RV.NET forum is that they should repost their answers and their time is not as valuable as yours.

Ding, ding, ding, we have a winner.

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