Gas cylinder level indicators

MikeBz

MikeBz

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How do they work then? I mean the magnetic strip things which purport to tell you how much is left in the cylinder.

I'm guessing that since they only 'work' when you're using gas it must be something to do with the cylinder cooling and the bit below the 'waterline' (liquid level) cooling more quickly than the bit above the level (higher heat capacity of the liquid). Maybe.

Presumably it should be placed at the bottom of the cylinder?

Mike
 
They exploit a principle known as "phase change". Specifically, crystals are sensitive to temperature, and can be designed to be, say, yellow, at +5c, orange at +10c, and red at +15c. (Example only)

The heat sensitive crystals are incorporated in a magnetic carrier which should be placed on the bottle so that the long side goes vertically, and crosses the level of liquid inside the bottle. As LPG is used up, a temperature differential between the liquid and the gas in the bottle is created by evaporation. This cold "band" passes through the wall of the cylinder and affects the crystals in the magnetic strip.

Errors are likely to be caused by the movement of the vessel making the liquid in the bottle move to and fro, thus increasing the width of the cold band. As one is really only interested in knowing when the level is towards the bottom of the bottle, this is not a critical signal problem.
 
I bought one a few years ago, and to be quite honest, I hardly ever used it. The boat it was intended for had the gas cylinder on deck and the guage used to be bady effected by the sun.

Current boat the cylinder is a very snug fit in the locker, so you can't read it anyway /forums/images/graemlins/grin.gif it only cost a couple of quid from a caravan shop.

Now I guesstimate capacity on usage and weight. I'd have thought the only really accurate way of measuring the gas level is by weight.
 
Alternatively get a see through bottle

Like this one available in 5kg and 10kg sizes from BP.
They are fibreglass and don't corrode either.
bp_gas_light_180x144.jpg


Or you can feel the bottle and detect the level by finding where the temperature changes.
 
[ QUOTE ]
The heat sensitive crystals are incorporated in a magnetic carrier which should be placed on the bottle so that the long side goes vertically, and crosses the level of liquid inside the bottle. As LPG is used up, a temperature differential between the liquid and the gas in the bottle is created by evaporation. This cold "band" passes through the wall of the cylinder and affects the crystals in the magnetic strip.

[/ QUOTE ]

Ah, so my guess was correct! Must be my lucky day.

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As one is really only interested in knowing when the level is towards the bottom of the bottle, this is not a critical signal problem.

[/ QUOTE ]

I wonder what proportion of the cylinder height is taken up by liquid when 'full'?

Tricky to guess when to get refilled even with the indicator, I suppose experience will help but as we don't have anywhere to carry a spare we don't want to risk running out.

Mike
 
I have a gaslow gauge and it gives a reasonable indication of amount of gas left. I don't understand it though, as it seems to be just a pressure gauge directly on the bottle. If there's any liquid in the bottle, then the pressure should be the saturation pressure at the ambient temperature; the pressure should start to fall only when the liquid has all gone and just the very last bit of gas remains. Can anyone explain how it works? Or have I only noticed it working as the pressure fell at the end of the bottle's capacity?

Derek.
 
On board ship - any liquified gas ballon was checked with a dial temp gauge ... in fact if you got one of those cheapo stick it dash temp / clock jobs from car mart ... that would do the job by moving the probe up / down vertically the wall of the cylinder.
 
I keep meaning to buy a cheap spring balance. The small Calor bottle has 4.5 kg of actaul gas in it.

I guess fisherpersons use them.
 
[ QUOTE ]
I wonder what proportion of the cylinder height is taken up by liquid when 'full'?

[/ QUOTE ] Looking at a 907 Gaz cylinder I estimate its capacity to be 6 litres and if I interpret the makings correctly it is actually 6.02.

They contain 2.72kg when full and an internet search has given me 0.57 to 0.58 as the density of commercial liquid butane at 15C.

2.72 kg is therefore 4.73 litres so in the case of 907 cylinders, they are about about 78% full but I'll leave you to work what that means in terms of the height of the cylinder taking the dished ends into account.
 
Now I have never tried this but apparently the best way is to trickle boiling water from a kettle down the side of the bottle. The difference in temperature becomes immediately apparent indicating the correct level.

I would rush outside and check this myself but its a chilly 15 degrees C outside this winters day.
 
The only real way is by weight.

I use a cheep bathroom scales. I know the weight of gas in the cylinder but not the total weight of gas and cylinder.

I have modified my scales to put a full mark at approx total weight of full cylinder and then and empty mark the weight of gas below that.

When I conect a new full cylinder I adjust the scale to show the full mark and as the the gas is used the mark will move towards the empty mark.

In my case the LPG I use is in 9Kg cylinders with an empty weight of between 10 - 12 kgs but the UK cylinders may be differnt capacities.
 
[ QUOTE ]
Looking at a 907 Gaz cylinder I estimate its capacity to be 6 litres and if I interpret the makings correctly it is actually 6.02.

They contain 2.72kg when full and an internet search has given me 0.57 to 0.58 as the density of commercial liquid butane at 15C.

2.72 kg is therefore 4.73 litres so in the case of 907 cylinders, they are about about 78% full but I'll leave you to work what that means in terms of the height of the cylinder taking the dished ends into account.

[/ QUOTE ]

Very useful, thanks!

Mike
 
True ... in fact in camping shops you can buy a plate that gas ballon sits on and the weight operates a pointer to show full or empty !

Yes the spring balance is a good way of doing it ... tare weight is stamped into the cylinder at top - so that and gas weight combined is what balance should indicate. OR best way to make sure you have it right ... get a new filled cylinder ... weigh it ... mark balance with perm. marker for full. Get empty cylinder and o similar ... no need to know kgs - just look at marks !
 
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its a chilly 15 degrees C outside this winters day.

[/ QUOTE ] Its no warmer in most coastal areas of the Uk on this summers day in flaming June
 
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n fact in camping shops you can buy a plate that gas ballon sits on and the weight operates a pointer to show full or empty !

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Do you know of any online suppliers ?
 
Sorry no ...

I can only suggest a trawl of Google etc.

Hants & Dorset Caravan Centre was where I got mine from ... they have a web-site - but UK to SA ? It was only about a pound as it's a plastic job ...

The guy who mentioned Bathroom scales ... that actually better ... bigger but probably more accurate ! Wouldn't take much to rip a B/ Scale apart and modify ? It's only a lever mechanism ...
 
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The guy who mentioned Bathroom scales

[/ QUOTE ] that me, but the big problem is the mechanical ones rust very quickly and the electronic ones turn off after a short time and requires to be reactivated by jumping on them,
 
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