Propane Cylinder worse when empty?

Our ancient camping fridge can be run off 240v, 12v dc and propane. Used it last weekend on propane and it barely cooled.

Back home it ran at 50F on propane but 30F on 240v. The bottle was nearly empty so I bought a new one, tried again and its on 28F (flat out).

I'd been told previously that the "quality" of the gas reduces as the bottle empties and the more volatile fractions go first but never really believed it.

Is this true or merely coincidence?

Peter

I have now heard about the quality of the gas reducing as the bottle empties. The gas regulator supplies the same pressure whether the bottle is full or low.

You have said that the bottle was nearly empty when to tried it back home and the fridge worked OK with a full bottle. I suspect that the bottle was almost empty when you used it on the previous weekend. These fridges do not use much gas.

We used an old, gas/electric refrigerato/freezer recently and used it continuaously for 2 weeks on the same caravan size gas bottle and did not run out of gas. Food was frozen all of the time.

Paul

If Propane is what you bought, then it is only Propane that should be in the 'can', whatever the cicumstances.

Mixtures are a different story.

Hi Peter, I think you will find that the problem is with the fridge not the gas, our first campervan was fitted with a 3 way fridge & as the years went by it got to the point where it was taking about 6 hours to get to operating temperature, a real PIA, I sought advice & was told that over time especially when standing for long periods in the off season they get for want of a better term "silted up", apparently & you can find this online or ask a friendly caravan engineer as I did, you can adopt a regime of turning it upside down & running it, from the mains I should add, then right way up & so on, it cured mine & looking on the bright side you wont have the rave getting it out that I had! If you succeed then embark on a regime of running it from time to time to keep it that way.

However as that experience marked me for life, when we aquired our latest van 18 months ago the man who had owned it ran it with an obscenely expensive Dometic fridge that had just about enough room for a bottle of milk & 2 pots of yoghourt inside, I went straight out & bought a 45 litre table top compressor fridge & stuffed it under the end of the bed, fastened down, it takes 8 minutes to get down to temperature!

cheers.

I think here it pays to get the LPG cylinder purged every now and then, they have a mixture of propane and butane depending on the time of year, and the gas mix tends to get a bit out of balance.

About 60 years ago we had a 2 way fridge, either 230v AC, or a kerosene(parafin) burner.

Ian S C

I can tell when my the bottle on webber bbq is getting close to empty as it takes longer to heat up and doesn't get as hot and i remember the gas hot water in a van i was living in was the same .

Possibly like a boiler , a full boiler has its water at boiling point ready to convert to steam but the less water in that boiler the less steam it could produce at any one time . Also tak e a look at your regulator they don't last forever and i have had a few fail or play up .

Door seals on those fridges are really critical also .

Ian SC,

I would rather a kero unit than lpg , i have heard of some three way fridges exploding usually when on gas .

Ian.

Sounds like the bottle was so close to empty the pressure in the bottle was insufficient to push enough gas through the regulator at the required pressure and flow rate. Ambient temp may have been a factor too, as warmer ambient temp will raise the pressure of the gas in the bottle, colder temps likewise reduce the gas pressure.

Thanks everyone, especially the hint about running the fridge upside down on the mains.

There was enough gas in the bottle to run a gas ring for a few minutes so dont think the bottle was completly empty when I exchanged it.

I suppose the real proof would be to have tried it back on the old bottle, if I'd thought seriously I would have taken another, didnt expect it to make any difference!

Peter

This will be an evporation type fridge. the gas flame is tiny, and can be deflected by dust or draught, it is a pain, but take the fridge out, clean all the dust and cobwebs from round the back, and light it, you could find that the jet is partially blocked, and the poor cooling is caused by the flame not getting to full size, or coming out of the jet at an angle which shoots the flame away from what it is supposed to be heating. If it works ok on the mains, it is not the fridge at fault.

Phil

It's very important to make sure the chimney is clear and line up properly, when working they work very well, but they do eat a lot of gas over a week!.

I think it's down to this: propane in a cylinder is in liquid form due to the pressure. As you use propane the liquid evaporates to yield the gas. The evaporation absorbs heat and lowers the temperature. At lower temperatures the liquid evaporates more slowly.

When the cylinder is full there is a lot of liquid and the temperature drop is small. When nearly empty the small amount of liquid remaining is chilled to a much lower temperature and can't evaporate fast enough to supply full pressure.

I think you will be able to feel the bottom of the cylinder getting cold when using it near empty. You could probably return to normal operation by warming it gently, a bowl of luke-warm water for example, but you do so at your own risk, obviously.

Just don't do as a university in Aus did about 50+ years ago, they were using 4 large cylinders on a project, it was stored in a wooden shed, and to keep it from getting too cool it had an electric blanket wrapped around it with a thermostat to control the temperature, you guessed it, the thermostat failed, and in the morning when everyone got to the site they found the shed with it's walls blown out, and the roof some distance away.

Ian S C

We have a propane cooker and know when a bottle is getting low because of the pungent smell, (not my cooking by the way) it gives off.

I relies on gravity to make the cycle work. I don't think you should actually run it upside down. The inversion just gives a chance to move the silt if it is blocking something.

The smell is more due to the 'smelly additive' (a safety measure as propane does not have a smell for us humans). It must clearly not all be evaporated before the gas bottle is empty, so has a slightly lower volatility and remains in solution until there is very little liquid propane in the bottle. The pungent smell is sulphur dioxide.