Gas cylinder empty or full?

[hillwalker]

I know this might be the silliest question of this year, but, how can I tell if a cylinder is full or not?

I can't remember whether or not the spare cylinder is a full one I brought from my old boat a year ago, or if it is one the previous owner left behind.

Is there an easy way to tell if its full or not.  (I realise I could just connect it and see if there is gas in it, but that doesn't tell me if its full or virtually empty). It's the little blue one.

David

[Don Reaves]

If you have two that are the same model, weigh them to see which is heavier. I have a fisherman's scale that I use for this purpose. If you only have one of each size, next time you fill them, weigh them before and after filling. Once you've done that, it will be clear when they need to be filled.

[Zanshin]

The weight difference is quite noticeable - but you'd need to get a feel of the empty weight at least once before doing that. A full container will not be 100% liquid, so you might be able to shake the canister and feel/hear the "sloshing" sounds.

[zaphod]

There will be a tare weight marked on the cylinder. Anything above that weight is propane, so with a scale and simple math you will know exactly how much is in it.

My fiberglass tanks are translucent so you can actually see the liquid level inside.

[pdodds]

Pour some boiling water over the tank and a condensation line will form on the outside of the the tank at the height the propane is at.

[hillwalker]

OK thanks, I don't have any scales I can use.  Tried the boiling water trick, no condensation formed anywhere, felt to be the same temperature all the way down so assume its empty, feels a bit light to be full to be honest.

Looks like I left a full one on my old boat!

David

[zaphod]

Oct 9, 2019 12:33:54 GMT hillwalker said:

OK thanks, I don't have any scales I can use.  Tried the boiling water trick, no condensation formed anywhere, felt to be the same temperature all the way down so assume its empty, feels a bit light to be full to be honest.

Looks like I left a full one on my old boat!

David

There will only be a frost or condensation line when propane is a actively being drawn out of the tank. The band of cold is caused by liquid propane changing state to gas, and that will only happen when propane gas is being drawn off the top. There are actually level indicator stickers you can get for your tanks that use that process to indicate liquid level.

If you check your bottle right after you cook a meal you may see a frost line.

[Mistroma]

I have never tried the following as I usually just weigh the cylinder and subtract the tare to get the weight of gas.

1) Turn the cylinder on its side and shake gently back and forth. It is "liquid petroleum gas" and you should hear it sloshing around. Of course completely full and totally empty might sound similar (Just spotted Zanshin's earlier comment).

2) Float the cylinders in a water bath and compare how high they float. I seem to remember that LPG is around 0.55 kg/l. A camping gas cylinder usually has a tare of around 3.65kg and a full fill weighs about 2.74kg, making 6.39kg. It should be pretty obvious which cylinder is full of LPG and which is empty. A full cylinder would be around 80% immersed and an empty one approx. 45%.

Never tried this but the theory is sound (though I've just returned from the taverna and had a rather nice meal with lots to drink and may not be thinking clearly).

[rene460]

Hi Hillwalker, have we enough gas to cook dinner is a question we all have to wrestle with.  And you don’t want to go to bed with not enough gas in the bottle to make the first coffee in the morning.

Unfortunately it is not easy to answer so precisely.  I keep meaning to take the luggage scale (which weighs to the nearest 10 gm) when I go to the boat, but when I remember to take it, the bottles are never empty.  Perhaps I should buy a second for the boat.  I have bought a little device which you hold against the bottle and it beeps if there is liquid inside at that point.  By moving it up and down, you can determine the level, so keep an eye out in camping or barbecue stores.  I assume it is ultrasonic but I don’t know.  It does seem to work.

As Zaphod says, methods which rely on the temperature difference only work when gas is being consumed as the temperature soon equalises once the usage stops.  And even then, the condensate does not form in warm dry atmospheric conditions, and on warm nights, the temperature difference can be difficult to detect.  I would not recommend submerging the bottle, although the principle is sound, as the bottles corrode readily enough in our marine atmosphere, and you don’t want to encourage more corrosion, especially in salt water.  In any case the density of the liquid varies slightly depending on the exact propane/butane mix unless it is essentially all propane, so the floatation method is unlikely to be more accurate than weighing.

It goes against the grain to refill a bottle before it is empty as most refillers do not weigh the bottle, though I have come across some that do.  To me the only way is to run it until the flame goes out, then replace the bottle.  This is easier if your gas locker is large enough for two bottles to be connected with a changeover valve, but my gas locker only holds one 2 kg bottle, so involves hanging over the stern with the spanner to change it.  I keep a spare in the life raft locker which is also adequately vented overboard, and fill the spare as soon as possible after changing over the bottles.  One bottle lasts us several months, but we only use it for the stern rail bar-b-que, and use liquid fuel for the stove in the cabin.

If you just want to know if there is some gas in the bottle or totally empty, I find that a full bottle is definitely heavy while an empty one is distinctly light.  For a part full bottle, I shake it a bit, and while I can’t hear sloshing, I can feel the momentum effect of the sloshing liquid inside.  It’s not a big force, but you can feel it.  But a full bottle does not slosh enough to feel either, it’s just heavy.

As already mentioned by others, weighing and using the tare weight stamped on the bottle should be a more precise method, though I am not sure how accurate the stamped figure is.  I suspect the manufacturers weigh one or a few samples of a batch and use the same number for all.  But it should be close enough for the purpose.

We are never far from a place where a bottle can be refilled, so, as long as I don’t leave one empty for too long, this system works for me.  If I was departing on a long trip with no opportunity to refill on the way, I would just refill at least one or possible both before departure to avoid running out.  So far, I have found both on the boat and even on long outback road trips with the caravan, as long as I start with at least one full bottle, I have enough.  But I always have that second bottle, as there is no warning when the bottle is about to become empty.  And it never runs out when you are not using it.

rene460

[zaphod]

The tare weight is accurate. There would be very little variation in weight for a mass produced cylinder.

Maybe it is different in other parts of the world, but around here propane is always either metered or weighed, so if your bottle isnt empty you only pay for the propane required to top it up.

You don't need any fancy gadgets to detect liquid level. Just buy a cheap fish scale. You don't need accuracy to the gram!

[ForGrinsToo]

My experience is that in the U.S., most refillers will typically glance at the weight, then fill with either one gallon (3.7 L) or two gallons (7.5 L) of LPG. Maybe 1 out of 3 will actually fill the bottle. Maybe they don't like to do the calculation? Anyway, I have an electronic luggage scale on board ($15) to check the weight at the beginning and end of each voyage. From memory, the tare is around 14 lb (6 kg) for an 11 lb tank (5 kg LPG: about 2.5 gal or 9.5 L). The 11 lb size seems to be a standard size on more recently designed boats.

Geoff

[johannes]

In my experience you always get a standardised fully filled cylinder in Europe, at least in Northern Europe.

[hillwalker]

Thanks Rene,

I bit the bullet and just took the cylinder to a dealer and swapped it for a new one, cost £30.

When I get back I noticed it has a plastic red seal on it to indicate it is a new unopened bottle.

It was then that I realised the one I took to the dealer (thinking it might be empty spare) also had a red plastic seal on it.

So now I am assuming a swapped a new bottle for another new bottle and paid £30 for the privilege!   I will never get rich!

David

[rene460]

Hi David, that sounds unfortunate, though I always keep the seal and place it back on the empty bottle when storing it, to keep dirt and water out.  But when I use Swap and Go, I keep the seal to avoid confusion.  

But the weight is very very different for a full bottle compared with an empty one.  So long as you are not interested in the last gramme or two, a fish scale or a luggage scale used with the stamped tare weight as Zaphod suggests, is quite adequate for the purpose.  It would cost less than you paid for the bottle to save the doubts worrying you again.

At least you now have the peace of mind of knowing that you are setting out with a full bottle.

Most refillers in this country just fill until liquid sprays out the vent and charge the listed price, so it clearly varies from between countries.  We have travelled the country on road trips and only found three that weigh the bottle and give any credit for what is in the bottle before they start.  I am sure the day is coming when the open vent method of filling will not be allowed.  However that will mean most gas retailers will just provide Swap and Go rather than put in the necessary facilities.

Rene460

[hillwalker]

Thanks Rene

David