propane canister (how to know how much is left inside)

[epowell]

Hi Folks
I have these old German/Austrian type of propane-butane cooking fuel canisters > I have 3 of them, and not much idea how much fuel is left inside each - they are heavy so I'd prefer not to drag them all around europe just for a few extra drops of fuel...
...does anyone know of a way to determine how much fuel is left inside each canister?
There is this pressure gauge but it seems just to stay on zero regardless of whether or not the canister is open or closed. Should this gauge help me to know how much fuel is inside?

...or is there another way? What about weight of the canister? Would weighing the canister help determine which canisters have more fuel inside?

Thanks
Ed

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[DuncanS]

If the gauge reads zero open or closed there is either no fuel left, or the pressure gauge is broken. Refill one of the canisters. Ask at the filling station how much an empty and full canister would weigh. Weigh it. This is the only reliable way to know. Then calibrate the others agains the full one. In the US, propane and butane are different fuels.

[epowell]

[epowell]

OK - I think it is solved.
My 3 canisters weight 6.9KG (the one that is in there now and reading zero pressure)
7.6KG
and last one 9.5KG

I swapped in there the 9.5KG one and now the pressure gauge is reading 6!

So this is good... it means I now have a way to determine how full/empty my canisters are. It was still giving fuel when reading zero - but it is seems the canister itself weights 6.1KG (that is what is written on the side), so when I have 6.9KG total weight, it means probably less than 1 KG of fuel. The canister feels pretty empty and when you shake it you can feel a little little bit left.

Still I would like to know how much a full one should weigh.

Does anyone know how much a full one weighs, or what the pressure gauge should read when full?

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[Abscate]

Propane density is 500 grams per liter around room temperature

Subtract the 6.1 kg tare weight from the measured, and double it Tom get liters in tank!

Tare is an interesting word we stole from the Arabs.
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[crazyvwvanman]

In the USA the empty weights of propane tanks are stamped on them by the manufacturer.

The pressure gauge is almost useless as a way of knowing how much is inside, other than empty or nearly empty.

6 bar indicates there is liquid propane inside, and winter has ended or the tank has been kept indoors.

Mark

[epowell]

OK, so the pressure gauge is not a fine indicator....
The tank I swapped in there has 9.6KG total weight so that means when I minus 6.1kg I have 3.5kg of propane which should be 7 liters. ???

I don't know how much was originally in that tank... probably almost full (5kg) because we already used that for a 3 week trip in 2016.
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[djkeev]

If younuse the tank, in most situations you will notice a freeze line on the exterior of the tank during use.
That is your liquid level.
I think you can splash some water on the tank if your humidity is too low to condense on the tank.

They make a stick on "gauge" that uses this temperature difference to indicate fill level.

Dave
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[epowell]

So I tried this method to determine the amount of propane still in the tank [pouring hot water down the side and feeling for where the cold propane starts]
https://www.youtube.com/watch?v=KBaHX_X-YcY

Doing it this way I could determine that my tank is half full. Funny thing is that after doing the hot water test and then reinstalling the tank, the pressure gauge now reads 11! ...so it seems that the gauge is also very sensitive to temperature > the hotter the higher the pressure.

I guess what I will now do it once a week I will do the hot water test, this way I can start to understand how much propane we are typically using per week, and how much I have left.
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[MarkWard]

I don’t have the same tank setup, but I always fill up before I head out on a road trip. We use the propane for cooking and the fridge. It will last a couple weeks. If we are headed into the boondocks and I see a place to fill and it’s been more than a week, I stop and top off. From memory, the westy tank holds 3 lbs of propane. You can do the conversion.

If I were in your situation, I’d fill a tank and get the full weight. Take your trip
and monitor your consumption. This will give you a baseline for future trips. We have rented campers in Germany and Switzerland. Both campers had “exchange” bottles. One connected and a spare. They were pretty compact and I recall they lasted about a week.
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[epowell]

We don't run a fridge at all so our consumption is much much less...
...but you are completely right that the best thing to do would be to fill it up 100% then weigh it, then keep track of the average usage.

Problem is that we would have to go thru Austria to fill this up.... a slight detour, but much better roads!
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[2dogs1van]

Finally, a topic on the Samba I know something about!
As a retired anesthesiolgist I can explain why a pressure gauge on a tank of propane will NOT tell you how much propane is in the tank. A tank of propane is analogous to a cylinder of nitrous oxide on an anesthesia machine. Like propane, nitrous oxide is stored in a cylinder as a liquid. When the cylinder is opened, the nitrous is vaporized and released as a gas. The pressure gauge on the cylinder will not start to drop until all liquid nitrous oxide is exhausted and the cylinder is nearly empty. Thus to measure how much nitrous oxide is in the cylinder anesthesiologists must disconnect the cylinder from the anesthesia machine and "weigh" it on our foot.
The same is true for propane in that it is stored in a tank in liquid form and vaporized when released. The tank's weight is the only way to easily assess how much propane is in the tank. By the time the pressure gauge drops, the tank is virtually empty.
In contrast, oxygen is stored in the tank as a compressed gas only (no liquid form) and thus the volume of oxygen in a tank can be calculated by simply reading the pressure on the gauge.

[Sodo]

[epowell]

At least the pressure gauge will tell you you are almost empty... right now, one tank still have usable gas - and you can even hear it when you shake the cylinder > but the gauge is on zero.

We are now 99% sure to go thru Austria. To minimize weight we will bring 1 almost empty cylinder and exchange it for a full one for 15eur in Austria... we will weight that full cylinder immediately, then at the end of the trip weight it again to know our average daily usage... as Mark suggested. My GF and I both agreed that the #1 priority is not to get into the mindset of being nervous and cheap with propane usage (she is constantly making tea )... because not staying in hotels it is right to afford at least unlimited propane use as a luxury. Cheap stuff anyway. And I hate being a watchdog for consumption control... so best to be 100% sure of having LOTS of propane
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[dobryan]

Always keep the GF happy.
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