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What is Liquefied Petroleum Gas?

What is Liquefied Petroleum Gas?

Shop for Gas regulators and hoses

Land-based gas drilling rig on a hilltop Liquefied Petroleum Gas, or LPG for short, is a mixture of two gases:

  • Butane
  • Propane

Around 60% of LPG is extracted from the ground or sea bed as natural gas, and the rest is made from the process of refining petrol.

Diagram with downward arrows showing gas being compressed into a liquid The gas is then compressed so much that it becomes a liquid which can be stored in small tanks and then released gradually to provide power.

Propane takes up about 270 times less space and butane about 230 times less space after compression, which means LPG is easily portable and lasts a long time.

Diagram showing liquid turning back into gas When you use LPG, the regulator ensures it is released at a safe and even rate from the cylinder through a valve. It turns from a liquid back into a vapour gas at this stage.
Picture of a woman holding her nose to avoid a bad smell Because LPG has almost no odour, manufacturers add chemicals to make a distinctive smell in case of a leak.
Propane, butane and patio gas cylinders In the UK, propane is normally stored in red tanks and butane in blue tanks. Green cylinders, often labelled as patio gas, usually contain a mixture of butane and propane. However, colours can vary in other countries.
Portable butane heater and small barbecue with food Butane gas is generally used for small appliances such as portable heaters, or outdoor appliances such as stoves and barbecues in the summer. It is less toxic than propane so you can legally store it indoors.

However, it doesn’t burn very well in cold conditions – less than 0°C – so it is often mixed with around 20% of propane, which will work at much lower temperatures.

Snow and sun depicting extremes of weather Propane has a boiling point (the temperature at which it turns from liquid gas to vapour form and can be used) of -42°C. This means that unless you live somewhere like the North Pole, you can use it all year round.

Propane remains in liquid form due to the pressure within the cylinder, and becomes a gas again as it’s released from the cylinder and returns to atmospheric pressure.

Patio heaters, gas torch, gas-powered car and gas barbecue with propane cylinder The convenience of being able to use propane in cold weather makes it popular with caravanners and an ideal fuel for household outdoor heating tanks, vehicles, gas torches, large barbecues and other appliances which need a powerful but portable heat source. However it is toxic, so must always be stored outside.
Picture of a bar of steel Many LPG cylinders are made of steel. This is because a strong metal is needed to cope with the varied pressures and temperatures that occur inside the cannister, but it does make them very heavy and difficult to move around.
Heavy caravan tilted downwards being towed by a car However, lighter containers are becoming more common, with many nowadays being produced in aluminium, fibreglass or plastic.

These lightweight cylinders are especially suitable for caravans, as they won’t significantly increase the vehicle’s noseweight and make it unbalanced at the front.

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Two translucent gas cylinders Translucent, or see-through, containers are becoming much more widespread. These are usually made of fibreglass or plastic compounds and show roughly how much gas is left inside.
Pressure gauge Some cylinders come with a pressure gauge which lets you monitor the gas level and acts as a leak detector. You can also buy them separately to add on.

Not all regulators include a pressure gauge port, but you can buy adaptors for them. For more information see: What gas regulator accessories are available?

Gas level indicator with cylinder Another useful accessory is a gas level indicator, which sticks magnetically to the side of the cylinder.

As the gas is used up, the temperature inside the cylinder begins to drop. Liquid crystals in the indicator react to this by changing colour, showing when you need to think about a refill.

Three different ultrasonic gas level indicators You can also get ultrasonic gas level indicators, which use the same technology as medical ultrasound scans.

There are various different designs on the market, but they all work by shooting an electronic beam into the cylinder. Some of the beam bounces back, and this shows whether or not there is liquid gas left in the tank at that point.

Diagram showing how ultrasonic gas level indicator pens work If there is no liquid gas present, the LED (Light Emitting Diode) display will turn red, and if the device detects liquid gas it will go green.

Take care to hold the indicator horizontally, otherwise the beam will point at an angle through the tank and you might get a false reading.

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