How Much Gas is Left in the Gas Bottle?
Checking the level of remaining gas, in a gas bottle, is an easy process.
To make sense, it helps to first explain how LPG works. LPG is stored under pressure, as a liquid, in a gas bottle. It turns back into a gas by ‘boiling’ into gas vapour. This happens at the very low temperature of -42°C. To boil, the liquid LPG draws heat from the steel walls of the gas bottle. This, in turn, makes the gas bottle feel colder than the ambient temperature. The gas bottle gets even colder when you are actually using the gas. Under the right conditions, when you are using gas very rapidly, ice can even form on the gas bottle!
So, we use this to tell how much gas is left in a gas bottle. How? Well, we pour hot water down the side of the gas bottle to heat the steel. The steel above the level of the gas will retain the heat longer than the steel below the level of the gas. This makes it feel warmer above and cooler below the gas level. The point at which you feel the temperature change is the level of the gas inside the bottle.
How to check how much gas is left in your gas bottle
This test works with either 45kg home gas bottles or Braai gas bottles
How full is the gas bottle? Do NOT use boiling water, as you would risk scalding yourself.
1. Water from the hot water tap of your home should work fine.
2. Using care, SLOWLY pour the hot water down one side of the gas bottle. More water is better, as it will make it easier to feel the difference in temperature.
3. A line of condensation may appear, indicating the gas level. If not: Wait a few seconds and then run your hand down the same side of the gas bottle, where you poured the water.
4. You should feel a change of temperature at the level of the gas. If you feel no difference, the gas bottle may well be empty.
The test works even better during or after you use one of your LPG appliances.
For example, if you have LPG hot water, do the test right after somone takes a shower.
Also, please remember that gas bottles are designed to be full at 80% or just over 3/4. This allows for the natural expansion of the gas during warmer temperatures.
For safety reasons, NEVER open the valve on an unattached gas bottle to check for remaining gas, even if you think it is empty.
Alternative Way to Check
An alternative way to check a Braai size gas bottle is by using a scale. Disconnect the bottle and place it on a scale, making sure the valve is firmly closed.
The tare (empty) weight of the bottle is stamped on the neck ring. The difference between the scale reading and the tare weight should indicate approximately how much gas remains in the bottle.
The ALVA Magnetic Gas Level Indicator can also be attached to your cylinder. Crystals in the indicator react to the temperature in the bottle to indicate the level.