Propane fill question

[12th_Man_Fan]

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.

[RinconVTR]

SaltiDawg wrote:

RinconVTR wrote:

SaltiDawg wrote:


It is my experience that a full 20# propane bottle will produce the same amount of work as 4-5 gallons of gasoline.

And this is impossible FYI. You're talking 1:1 the same energy content LP to Gasoline? Not possible...

Actually you are demonstrating a lack of understanding of Thermal Efficiency considering different fuels and how it relates to fuel efficiency in a small four-cycle engine. You cited a home heating fuel comparison page and compared the available work or heat energy taken from that page for the two fuels on a per gallon basis.

In the case of home heating, the thermal efficiency of an older oil (diesel) is about 80%. On a new condensing furnace using Natural Gas or Liquid Propane thermal efficiencies approaching 95% can be attained.

In a small four-stoke engine you have assumed that the efficiency of that engine using gasoline is the same as using LP. Than telling me that my assertion about in my experience that a 20# bottle is about the same as 4-5 gallons of gasoline is impossible. Let me absolutely assure you that in my experience and that of many, many other posters over in the US Carb forums that approximation is right on.

So, while gasoline does have a higher amount of available energy when compared to LP, the increased engine efficiency tends to mitigate that difference.

.

Hey...you can try to talk smart all you want, but you're talking jiberish and strict theory with a whole lot of opinion. NOT REALITY.

One, you've taken a simple chart I posted beyond what it was ever intended to prove and I never once mentioned home heating oil. Stop taking my post so far out of context.

And an LP motor vs equivalent HP gas motor will NEVER run as long on an equal number of "liquid gallons" under the same load. Never. I can show you chart after chart after chart, and also compare my own experience with generators. I'm game to play any time bud. Any. Time.

And the very same situation is currently being play in CNG powered semi's on the road right now. They will never reach the the "MPG" for the sake of simplicity, to diesel. The ROI advantage is CNG right now but its 3-4 years based on the current price of each fuel. That can change over night, but the "MPG" values do not.

Both comparisons are pretty close but will never be equal.

Get. A. Clue.

[Dutch_12078]

The OPD is a failsafe device that is not intended for use as a fullness measuring device. Portable DOT cylinders should either be filled by weight or by using the liquid level indicator ("spitter valve") if equipped.

[Likes_to_tow]

When we brought our "new to us" two year old 5th wheel home from the dealer I noticed the smell propane very strong. Upon inspection of the two 30lb cylinders I noticed one was venting propane uncontrollably. I had the valve shut off. The dealer had topped both tanks before we left as part of the deal. Now what should I do? After a moment or two of panic, I disconnected the tank and carried it 100yds into an open hay field behind my house and just let it set there. Eventually it stopped venting and I brought it back near the house. I called the dealer on Monday morning and he said the OPD valve must have been defective allowing the tank to be overfilled !!!! He instructed me to return the tank in exchange for a new one. Now here is the problem I have with this. If the OPD valve can be "defective" who's to say this cannot happen to anyone anywhere? I don't trust the OPD to make the determination of how much it will hold. I fill my tanks to less than full always. Have the tanks weighed and determine how many gallons will take it to 3/4 full.

[Ron3rd]

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%.

X2. No worries. Let 'em filler 'er up till the gas shoots out.

[SaltiDawg]

RinconVTR wrote:

SaltiDawg wrote:


It is my experience that a full 20# propane bottle will produce the same amount of work as 4-5 gallons of gasoline.

And this is impossible FYI. You're talking 1:1 the same energy content LP to Gasoline? Not possible...

Actually you are demonstrating a lack of understanding of Thermal Efficiency considering different fuels and how it relates to fuel efficiency in a small four-cycle engine. You cited a home heating fuel comparison page and compared the available work or heat energy taken from that page for the two fuels on a per gallon basis.

In the case of home heating, the thermal efficiency of an older oil (diesel) is about 80%. On a new condensing furnace using Natural Gas or Liquid Propane thermal efficiencies approaching 95% can be attained.

In a small four-stoke engine you have assumed that the efficiency of that engine using gasoline is the same as using LP. Than telling me that my assertion about in my experience that a 20# bottle is about the same as 4-5 gallons of gasoline is impossible. Let me absolutely assure you that in my experience and that of many, many other posters over in the US Carb forums that approximation is right on.

Propane has an Octane of somewhere around 105 IIRC. Also, no energy is required to atomize propane as compared to gasoline's energy requirement. And, in the case of gasoline, the gasoline is really not fully atomized, but rather is transformed to an aerosol mist comprised of small droplets.

So, while gasoline does have a higher amount of available energy when compared to LP, the increased engine efficiency tends to mitigate that difference.

In reaction to your aggressive response to a post intended simply to help, I'll not be viewing your posts.

[red31]

smkettner wrote:

I am looking for an explanation on how all these posts think you can deliberately fill to 100% gross volume vs. 100% rated capacity.

Fill to 80% by volume when below zero and then wait till it warms up or travel to a warmer climate.

80% is a different mass at every temp, 40# is 40# @ -10F and 130F.

There is still the case when OPD is broke and one gets 5+ gallons of propane in a 20# cylinder.

[RinconVTR]

dougrainer wrote:

RinconVTR wrote:

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.

THERE IS NO AIR IN A LP TANK/CYLINDER. There is only LP vapor that is produced from the LP liquid in the tank. Soooooo, for a 100% full liquid tank, there is NO ROOM for the Liquid to vaporize. As I stated, 100% liquid will cause Liquid to flow OUT when the tank valve is opened and that will destroy the LP regulator. Doug

I put "air" in quotes...referring to the 20% area which is not liquid. We are saying the very same thing otherwise.

[time2roll]

red31 wrote:

smkettner wrote:
First of all anyone that talks about overfilling a propane bottle to 100% of gross volume needs to explain how they are getting past the OPD valve that limits the fill to 100% of rated volume.

The OPD is not functioning correctly. If the OPD does not shut off at below 80% (40# in OPs case), no one will know it is not working. It is not the primary device used to fill.

If the filler stops filling cuz the scale tips, the OPD did not engage.
If the filler stops filling cuz 'liquid' is coming out the fixed max liquid gauge, the OPD did not engage.

Since 80% of container volume is based on 40F, any temp above 40F, the OPD should stop filling since the volume of liquid is larger. The dip tube length (DT) is based on 40F/80%, specific gravity of .504-.510 .

4-4.3.3 Where used, the volumetric method shall be in accordance
with the following:
(a) If a fixed maximum liquid level gauge or a variable liquid level
gauge without liquid volume temperature correction
is used, the liquid level indicated by these gauges
shall be computed based on the maximum permitted
filling limit when the liquid is at 40°F (4°C) for aboveground
containers or at 50°F (10°C) for underground
containers.

The safety valve is there for malfunction.
I am looking for an explanation on how all these posts think you can deliberately fill to 100% gross volume vs. 100% rated capacity.

[red31]

wnjj wrote:

Also consider that I only jumped into this mess when it was claimed that a 100% full cylinder wouldn't allow anything to flow out of it.

There's 100% full and then there is 100%+ full, the pressure has risen due to compression of the liquid. If the regulator is near the container, like a gas grill, there is not much extra volume for the liquid to vaporize. Liquid could be present all the way up to the reg's orifice. The vaporization happens inside the reg making it very cold if there is much demand. The cold slows down the vaporization. ...

[red31]

smkettner wrote:
First of all anyone that talks about overfilling a propane bottle to 100% of gross volume needs to explain how they are getting past the OPD valve that limits the fill to 100% of rated volume.

The OPD is not functioning correctly. If the OPD does not shut off at below 80% (40# in OPs case), no one will know it is not working. It is not the primary device used to fill.

If the filler stops filling cuz the scale tips, the OPD did not engage.
If the filler stops filling cuz 'liquid' is coming out the fixed max liquid gauge, the OPD did not engage.

Since 80% of container volume is based on 40F, any temp above 40F, the OPD should stop filling since the volume of liquid is larger. The dip tube length (DT) is based on 40F/80%, specific gravity of .504-.510 .

4-4.3.3 Where used, the volumetric method shall be in accordance
with the following:
(a) If a fixed maximum liquid level gauge or a variable liquid level
gauge without liquid volume temperature correction
is used, the liquid level indicated by these gauges
shall be computed based on the maximum permitted
filling limit when the liquid is at 40°F (4°C) for aboveground
containers or at 50°F (10°C) for underground
containers.

[wnjj]

dougrainer wrote:

wnjj wrote:
If you have a full container of liquid under pressure, the second you open the valve there is an increase in volume (the hose) which will drop the pressure rapidly. The first liquid to enter the hose will immediately boil off to gas. Now if the cylinder was at such a high pressure that adding the hose volume doesn't drop it below vapor pressure then liquid could flow to the regulator.

NOT TRUE. PERIOD. Doug (35 years as an RV Tech and 35 years Licensed by the Texas Railroad Commission, which trains and license LP service and fillers). Liquid also will into the piping even at 80% fill by the sloshing while driving. NOT so much a problem on DOT tanks but a common problem on Motorhome ASME tanks. Since the standard of auto cut off valves years ago this type problem has been minimized.

I'm not trying to be argumentative or "right" but really want to understand how this works.

Do you still think what I wrote above is not true if you consider a cylinder that's just sitting full with the valve closed, not one in motion with it open?

I may be remembering my college thermodynamics wrong but why would opening a valve on a full tank cause liquid to expel when it would turn to gas as soon as it hits the low pressure area? Please help me to understand by explaining the physics behind it.

Also consider that I only jumped into this mess when it was claimed that a 100% full cylinder wouldn't allow anything to flow out of it.

I get that in the real world, there is sloshing and valves aren't left closed while travelling.

[beemerphile1]

red31 wrote:

beemerphile1 wrote:
I don't understand all the confusion on this subject which gets rehashed regularly.

An LPG cylinder is filled to 80% of WC (water capacity). That means a 40# rated cylinder holds, guess what, 40# of LPG when filled to 80% of WC.

cuz folks keep posting incorrect info.

42% of WC is not the same as 80% WC. WC is in lbs not vol.

80% WC does not account for the sg difference. 42% does.

http://www.mantank.com/products/dotproducts/5-420steel.htm

http://www.nfpa.org/Assets/files/AboutTheCodes/58/58-98-PDF.pdf

You're right, I corrected the error in my post. I was typing one thing and thinking another thing causing the error.

[2oldman]

RJsfishin wrote:
its not hard to tell those that don't have the foggiest idea, but insist on posting anyway,.

There's no such thing as a stupid answer. :W

[dougrainer]

wnjj wrote:

dougrainer wrote:

RinconVTR wrote:

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.

THERE IS NO AIR IN A LP TANK/CYLINDER. There is only LP vapor that is produced from the LP liquid in the tank. Soooooo, for a 100% full liquid tank, there is NO ROOM for the Liquid to vaporize. As I stated, 100% liquid will cause Liquid to flow OUT when the tank valve is opened and that will destroy the LP regulator. Doug

If you have a full container of liquid under pressure, the second you open the valve there is an increase in volume (the hose) which will drop the pressure rapidly. The first liquid to enter the hose will immediately boil off to gas. Now if the cylinder was at such a high pressure that adding the hose volume doesn't drop it below vapor pressure then liquid could flow to the regulator.

NOT TRUE. PERIOD. Doug (35 years as an RV Tech and 35 years Licensed by the Texas Railroad Commission, which trains and license LP service and fillers). Liquid also will into the piping even at 80% fill by the sloshing while driving. NOT so much a problem on DOT tanks but a common problem on Motorhome ASME tanks. Since the standard of auto cut off valves years ago this type problem has been minimized.