LPG Refillable Gas Bottles and Gas Tanks Solutions

Gas system in caravans (cars and caravans), just like at home, is using propane-butane gas or LPG (a liquefied mixture of propane and butane). LPG at room temperature and at normal pressure is in gas phase and liquefies when its pressure is above 2.2 atmospheres. The gas is pumped into the cylinder at a pressure of 6 atmospheres. Gas in the cylinder being at a pressure higher than 2.2 atmospheres is a liquid gas that accumulates at the bottom of the cylinder. Gas in gas phase accumulates in upper part of the cylinder. Cylinders in which LPG is stored and transported are usually filled to 80% or 85% volume in order to avoid bursting of the cylinder by the liquid which develops when the liquid gets too hot.

For cookers, burners, refrigerators, water heater etc. gas is used in the gas phase. Gas is taken from the top of the cylinder. In autogas liquid gas is taken from the bottom of the cylinder to supply the engine, which is then evaporated in converter (this is usually achieved by having engine coolant circulated through a heat exchanger that transfers heat from that coolant to the LPG).

Common caravans gas cylinders are:

1. Traditional exchangeable cylinders (filled by the weight to not exceed 80% of the filling), these cylinders are usually equipped with a simple outlet valve with a mandatory safety valve set at 27bar pressure. Due to the risk of overfilling these cylinders require special filling equipment.
   • Steel gas cylinders – available in any size, for example 11KG – around 20 liters of gas (1KG = around 2 Liters of LPG)
   • Composite gas cylinders for example NANO, GreenGas, Hexagon Ragasco
   • Aluminum gas cylinders. For example Campingaz catridge (often without valve)

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2. Filling bottles with built-in OPD valve (Overfill protection device) – preventing volumetric overfilling of the cylinder. This valve is equipped with a floater that cuts off the gas supply when liquid gas reach 80% of the cylinder. Due to the convenience of use, cylinders with an OPD valve can be equipped with a single inlet and outlet like in standard exchangeable cylinders or with a separate inlet and outlet, which makes it easy to connect the cylinders into sets and does not require disconnecting the cylinder from the installation during filling. Separate inputs and outputs can be realized by separate valves or integrated called Multivalve. 

The biggest advantage of self-filling cylinders and tanks is independence from the specific cylinder supplier, especially when traveling.

• Steel gas cylinder – e.g. Gaslow, GZWM
• Aluminum gas cylinder – Alugas
• Composite gas cylinder – Safefill, GasBank

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3. External filling tanks with liquid gas output – these tanks are equipped with exactly the same valves as some steel cylinders with separate inlets and outlets. They are often called 4-hole Dutch type tanks or with 4 holes plate tanks in which the valves are mounted separately: inlet (with 80% cut-off), outlet (with solenoid valve or manual valve), safety relief valve (set to 27 bar), level indicator (float arm inside the tank rotating a magnet, which rotates an external gauge). The main difference between the autogas tank (which can also be 4 hole) and gas phase tank is the factory installed tube gas consumption.  In gas phase tanks this pipe reaches the top of the tank, while in autogas tanks it takes liquid gas from the bottom of the tank. It is very important to position the tank during assembly.

4-hole tanks types are:

• Cylindrical gas tank with mounting legs (STAKO)
• Cylindrical gas tank without legs (manufactured by GZWM – Grodkowskie Zakłady Wyrobów Metalowych)
• Toroidal gas tank (STAKO)

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