Extra propane tank

Ultimately over the years I have use nearly all the suggestions for carrying a spare propane container. I finally said "enough" and got one of the multi-application Extend a Stay Brass valves and 20 foot of hose. Got lazy and paid to have it installed, but when I traded the unit, I removed it myself and will install it on the unit as soon as I can. A little pricey up front, but pays for itself in that it ends the hassle and worry.

hipower wrote:

Clay L wrote:

hipower wrote:

Clay L wrote:


Does anyone know what pressure is required to cause venting? With that info one could use the Ideal Gas Law to calculate the temperature at which venting would occur.
SNIP

The vent pressure of most LP tanks is 250 psi. Some are built to a comparable standard and have a rating of something around 300+/- psi, but were intended for propylene service, not propane. I mention this only because I have seen those tanks repurposed by unknowing individuals and it causes an undue risk in propane service due to the higher relief valve setting.

I found a chart that shows that propane at 80 F will have a pressure of 140 psi. Using the ideal gas law I found that the temp would have to go to 500 F before the tank pressure reached 250 psi. That seemed high and even though the calculation is simple I used a couple of on-line calculators and got the same answer.

The chart is HERE and one of the calculators I used is HERE

So unless I did something dumb (that's always a possibility) it doesn't appear that an enclosed compartment, truck or car interior is going to get hot enough to cause venting.

The variable that you must consider is when someone overfills the cylinder. A little rarer today with the OPD valves required, but they are mechanical float devices that can fail. They can also be overridden by a high pressure/volume filling pump like those used on propane delivery trucks. One of the reasons suppliers don't want to fill smaller containers from their bobtail trucks.

If you want to check that your tank is properly filled simply look at the data on the collar of the cylinder. The tare weight of the cylinder will be there along with the WC (water capacity) number. Tare is obviously the empty weight of the cylinder while the WC times .42 provides the capacity of the cylinder in pounds of propane. Add the two numbers together and you will have a total weight for a full cylinder. Eg: a 20# cylinder with a 18# tare weight and 47.6 WC will weigh 38# full. Anything over that is overfilled anything less obviously is underfull.

Many of the exchange companies have established policies of underfilling to avoid liability issues with overfilling by minimally competent fillers. We frequently see these cylinders at 15-18# of propane when filled. This is only an issue when it comes to filling your cylinders more often or if you are paying a price equal to an actual 20# fill. Then it is a rip-off.

Shouldn't be a big problem because usually the supply tanks are above ground and would be very close to the ambient temperature. Although you will find some supply tanks underground, most are above.

Clay L wrote:

hipower wrote:

Clay L wrote:


Does anyone know what pressure is required to cause venting? With that info one could use the Ideal Gas Law to calculate the temperature at which venting would occur.
SNIP

The vent pressure of most LP tanks is 250 psi. Some are built to a comparable standard and have a rating of something around 300+/- psi, but were intended for propylene service, not propane. I mention this only because I have seen those tanks repurposed by unknowing individuals and it causes an undue risk in propane service due to the higher relief valve setting.

I found a chart that shows that propane at 80 F will have a pressure of 140 psi. Using the ideal gas law I found that the temp would have to go to 500 F before the tank pressure reached 250 psi. That seemed high and even though the calculation is simple I used a couple of on-line calculators and got the same answer.

The chart is HERE and one of the calculators I used is HERE

So unless I did something dumb (that's always a possibility) it doesn't appear that an enclosed compartment, truck or car interior is going to get hot enough to cause venting.

The variable that you must consider is when someone overfills the cylinder. A little rarer today with the OPD valves required, but they are mechanical float devices that can fail. They can also be overridden by a high pressure/volume filling pump like those used on propane delivery trucks. One of the reasons suppliers don't want to fill smaller containers from their bobtail trucks.

If you want to check that your tank is properly filled simply look at the data on the collar of the cylinder. The tare weight of the cylinder will be there along with the WC (water capacity) number. Tare is obviously the empty weight of the cylinder while the WC times .42 provides the capacity of the cylinder in pounds of propane. Add the two numbers together and you will have a total weight for a full cylinder. Eg: a 20# cylinder with a 18# tare weight and 47.6 WC will weigh 38# full. Anything over that is overfilled anything less obviously is underfull.

Many of the exchange companies have established policies of underfilling to avoid liability issues with overfilling by minimally competent fillers. We frequently see these cylinders at 15-18# of propane when filled. This is only an issue when it comes to filling your cylinders more often or if you are paying a price equal to an actual 20# fill. Then it is a rip-off.

hipower wrote:

Clay L wrote:


Does anyone know what pressure is required to cause venting? With that info one could use the Ideal Gas Law to calculate the temperature at which venting would occur.
SNIP

The vent pressure of most LP tanks is 250 psi. Some are built to a comparable standard and have a rating of something around 300+/- psi, but were intended for propylene service, not propane. I mention this only because I have seen those tanks repurposed by unknowing individuals and it causes an undue risk in propane service due to the higher relief valve setting.

I found a chart that shows that propane at 80 F will have a pressure of 140 psi. Using the ideal gas law I found that the temp would have to go to 500 F before the tank pressure reached 250 psi. That seemed high and even though the calculation is simple I used a couple of on-line calculators and got the same answer.

The chart is HERE and one of the calculators I used is HERE

So unless I did something dumb (that's always a possibility) it doesn't appear that an enclosed compartment, truck or car interior is going to get hot enough to cause venting.

Clay L wrote:
I have never seen a propane tank that was filled properly (to 80%) vent due to a normal temperature increase.

Does anyone know what pressure is required to cause venting? With that info one could use the Ideal Gas Law to calculate the temperature at which venting would occur.

From my design engineering days for the automotive environment I know that under dash temps can reach over 200F in direct sun in the AZ desert. (black dash, black car)

CO law allows propane tanks under 40 pound capacity to be transported in a car or car trunk when secured in an upright position. I would expect a closed bay compartment would be the same.

That being said, a defective valve that leaks would not be a good thing in an enclosed area.

We had an unusual leak in the first tank in our 2001 Adventurer. There's a releif plug welded in the bottom of the permanent tanks that's supposed to blow out and let gas escape in case of a fire. It's lighter gauge metal than the rest of the tank so it blows out first and the entire tank doesn't turn into flying shrapnel.

The plug is supposed to be continuously welded around the entire perimeter. Ours wasn't. There was a section about 1/2" long that didn't get welded. On really hot days the pressure in the tank would increase just enough for the gas to leak through the unwelded area.

Unfortunately we found the problem on the 4th of July when all the kids were running around the campground with fireworks. We had to call a local gas company to drain the tank. We spent the holiday without gas and had the tank replced the next week. Fortunately the tank had a 10 year warranty so we only had to pay for another tank of gas.

Clay L wrote:
I have never seen a propane tank that was filled properly (to 80%) vent due to a normal temperature increase.

Does anyone know what pressure is required to cause venting? With that info one could use the Ideal Gas Law to calculate the temperature at which venting would occur.

From my design engineering days for the automotive environment I know that under dash temps can reach over 200F in direct sun in the AZ desert. (black dash, black car)

CO law allows propane tanks under 40 pound capacity to be transported in a car or car trunk when secured in an upright position. I would expect a closed bay compartment would be the same.

That being said, a defective valve that leaks would not be a good thing in an enclosed area.

The vent pressure of most LP tanks is 250 psi. Some are built to a comparable standard and have a rating of something around 300+/- psi, but were intended for propylene service, not propane. I mention this only because I have seen those tanks repurposed by unknowing individuals and it causes an undue risk in propane service due to the higher relief valve setting.


I find the general paranoia about propane stored in unvented compartments interesting when we consider that nearly every coach or trailer has pressurized LP lines running throughout them and we rarely have anyone discussing the leak potential of those lines. Most of us operate our refers while traveling and would not consider shutting off the LP supply to avoid those potential leaks.

I would worry more about vibration causing a line leak than a venting tank in storage, particularly one that is out of the direct sunlight.

I have thought about a spare tank for my 5th wheel but one thing concerns me. There are some bridges and tunnels that will not allow you to carry a spare tank. The Chesapeake bay bridge tunnel is one route you will not be allowed access to

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COMPRESSED GAS REGULATIONS
For Non-Commercial Vehicles


Maximum capacity: (a) Not more than two non-permanently mounted containers having maximum individual capacity of 105 pounds water capacity or 45 pounds LP-Gas each, or one container having maximum capacity of 60 pounds LP-Gas, or (b) not more than two permanently mounted containers having maximum total capacity of 200 gallons water capacity LP-Gas when used as a motor fuel. Tanks must meet the approved standards of the Department of Transportation and are subject to inspection at toll plaza. They must be properly secured and valves closed while crossing the facility.


For a printable version of the Chesapeake Bay Bridge-Tunnel's current Toll Schedule, click here. (Adobe Reader Required)

I have the small one 5 lb +/- gallon

Five pounds or five gallons? Not that it matters, but I have one of those five pounders, which isn't much bigger than a gallon milk jug and it's REAL handy! Also easy to stow.

If yours is in fact the more standard twenty-pounder ("five gallon"), you'll need a bit more space...

I agree with the previous poster re. little danger from overpressure leaks, especially since your cylinder is new and literally can't be filled beyond 80% of capacity. As noted above, transportation inside vehicles is allowed so long as the cylinder's kept upright. Most folks use milk crates for that.

If you're nervous about the milk-crate-in-closed-bay idea, you might drill some ventholes in the floor of whatever bay you put the bottle in.

I have never seen a propane tank that was filled properly (to 80%) vent due to a normal temperature increase.

Does anyone know what pressure is required to cause venting? With that info one could use the Ideal Gas Law to calculate the temperature at which venting would occur.

From my design engineering days for the automotive environment I know that under dash temps can reach over 200F in direct sun in the AZ desert. (black dash, black car)

CO law allows propane tanks under 40 pound capacity to be transported in a car or car trunk when secured in an upright position. I would expect a closed bay compartment would be the same.

That being said, a defective valve that leaks would not be a good thing in an enclosed area.