ELGAS Knowledge Hub

How do LPG Tanks and Cylinders work

23 Jun, 2023 | Business LPG, Residential LPG

In this article:

Detailed working of LPG storage - pressure, pigtails, piping and more.
How LPG Tanks and bottles work

An LPG gas cylinder works when the LPG, stored as a liquid under pressure, turns back into gas by releasing some of the pressure in the gas cylinder.  

LPG is generally stored, as a liquid, in steel vessels ranging from small BBQ gas bottles to larger gas cylinders and storage tanks.

LPG gas bottle sizes vary, based on application and demand.

What are LPG Cylinders made of

LPG tanks are typically made of welded steel, aluminium or composites. Steel is by far the most common material, as it is the easiest to fabricate and it is a low cost material. Some cylinders are made of aluminium or composites to save on weight. Aluminium is quite common for forklift cylinders, relating to safe lifting. The use of aluminium keeps the weight down to allow for more gas whilst still staying within the safety weight limits. The most recent innovation is the composite cylinder. These are typically fiberglass with a high impact plastic outer shell. Some have an inner lining of HDPE whilst other have a thin steel liner. 

LPG (Propane) Liquid Changes to Gas – Vaporisation

Did you know that every time you turn on one of your gas appliances, the LPG gas cylinder works (propane tank works) as your gas starts to boil? If you could see though the steel, you would also notice that it looks just like water boiling.

The big difference is that it happens up until -42°C or -44°F. This is vaporisation, which is how LPG – propane – goes from liquid to vapour (gas).

Water boils at 100°C or 212°F, becoming a gas (steam). In contrast, LPG boils at -42°C or -44°F, becoming gas vapour. LPG stays liquid because it is under pressure in an LPG cylinder (propane tank). As a liquid, it looks a lot like water. It is colourless and odourless in its natural state.

The LPG gas vapour is held in the top of the LPG bottle and the liquid LPG at the bottom.

Gas Line Connection

The gas line pigtail or regulator screws into the large female threaded opening on the side of the valve. It is unique in that it has a left-handed or reverse thread. So, to tighten it, you turn the connector anti-clockwise. Tightening is achieved either with a wrench or by turning a hand wheel.

You should always do a soapy water leak test after every reconnection. LPG Gas Cylinder Works (Propane Tank Works) by Turning the Gas Valve Hand Wheel.The LPG gas cylinder works (propane tank works) by turning the hand wheel anti-clockwise to start the flow of gas, but you should avoid turning it hard to the open stop.

Located on the top of the POL valve, the gas valve hand wheel controls the flow of gas, once the connection is secure. Opening the valve 2 or 3 turns is all you need. You shut the gas off by turning the hand wheel clockwise, tightening firmly by hand only.

CAUTION: Never open the valve when unattached

Pressure Relief Valve

The pressure relief valve is the single most critical safety feature in how an LPG cylinder-bottle works (propane tank works). It is incorporated within the POL valve and appears as the protrusion opposite the main connection. It usually incorporates some kind of plastic dust cover that should be left in place. Pressure relief valves are designed to relieve excess pressure that might result from overfilling or exposure to excessive heat or fire. The function of a pressure relief valve is to keep a cylinder from rupturing in the unlikely event of excessive pressure build-up.

The pressure relief valves are held in the closed position by the force of a powerful spring inside. As long as the pressure is less than that of the spring, the valve will remain closed.

If the pressure rises beyond safe levels, the LPG gas cylinder works (propane tank works) when the pressure relief valve opens to vent the excess pressure.

If this happens, you may hear a hissing sound and see cold gas vapour being released. Once sufficient pressure is released, the valve closes.

If this ever happens, just stay clear of the area and let the gas dissipate.Having the pressure relief valve releasing gas is a rare event. Most people will never experience venting.

You should also call your LPG supplier, from a safe location, and advise them that your gas cylinder is venting gas.

Do not use your mobile phone, any electrical devices or other ignition sources near a venting gas cylinder.

Final Thoughts

An LPG gas cylinder-bottle works (propane tank works) unnoticed after evolving over many decades into a very safe storage and gas delivery system.

They are also easy to operate, requiring little attention until they need refilling.​

New Residential LPG customer?

New Business LPG customer?

Existing ELGAS customer?