LPG Cylinder Types

In New Zealand there are two regulatory bodies who approve LPG Cylinders.

The most common body is the Department of Labour, Explosives and Dangerous Goods Division. This Department controls the approval and operation of all domestic and commercial gas cylinders within New Zealand. This includes all LPG cylinders other than those used as Automotive Fuel Cylinders, i.e. to store fuel to power a vehicle, which are approved by the Land Transport Safety Authority (LTSA).

The LPG cylinders approved by the LTSA are liquid withdrawal cylinders that feed Liquid LPG to the LPG regulator system where it is vapourised and then fed to the LPG mixer on the engine. These cylinders are only approved as cylinders to serve this function; they are NOT approved as Vapour withdrawal cylinders as well. I have seen several such modified cylinders through my Cylinder Test Station over the years and have been required to remove the vapour valves from these cylinders before completing the testing procedures for them. This has caused some consternation to the owners, but when the reasons are explained I hope they are able to see why. These cylinders are not designed to safely supply LPG Vapour to a LPG Vapour regulator. If you inadvertently do supply Liquid LPG to a domestic LPG regulator, there is no way of knowing what the pressure shall be on the low-pressure side of the regulator. It will try to regulate the liquid, which will promptly vapourise after passing through the regulator, which means it could be as high as 100psi or more. This is not a good situation to be in, as it can damage the LPG regulator and any equipment connected to the system, as well as cause a rather dangerous situation inside your motorhome.

All LPG cylinders used to supply LPG Vapour must be approved by the Department of Labour and if manufactured after 1980 must also have a LAB No stamped on the cylinder that shows this approval. If a filling station is unable to identify the approval for a cylinder, it is not permitted to fill the cylinder. Like wise if the cylinder has not been retested within the last 10 years it is not permitted to fill the cylinder. You will in either case be referred to a Gas Cylinder Test Station.

There has been a bit of inquiry lately regarding the use of fixed LPG cylinders, similar to automotive fuel cylinders, for use in motorhomes. Yes there are approved cylinders available, however I advise you to think about their pros and cons before leaping into the installation of one.

First of all remember that 1 litre of LPG weighs approx. 0.5kg. 
When you fill a fixed cylinder at the LPG vehicle pump you are paying by the litre.
When you are refilling a portable LPG cylinder you are paying by the kilogram.
So the pump price of say 60 cents per litre equates to approx. $1.20/kg. (9kg=$10.80)

I know of areas within New Zealand, where a refill of a 9kg cylinder does infact cost $10.00!
Also when you run out with a fixed system you have to take the whole motorhome to the fill station to have it refilled. Also the tank is really a hand made item and is thus not a cheap item to purchase and install. Don't forget that it must come out in 10 years time for a retest as well.

The choice of LPG Vapor regulator system should also be carefully considered at the planning stage as well. There are now some regulators that have inbuilt excess flow systems. DO NOT use them as they will cause all sorts of problems with appliances, that will be rather difficult to fault find, believe me.

I consider the 'clip on' regulator system to be the best, if the original Danish system is used. This system is very reliable and easy to use. But be warned there is a regulator of this type that has a built-in excess flow valve as well! There is no need to use a regulator able to supply greater than 2kg/hour either if you are using a standard 9kg sized cylinder, as you will not be able to even draw 1 kg/hour from a 9kg cylinder. However that is generally quite adequate for the standard motorhome installation.

I hope this article helps you with your LPG systems and thus increases the enjoyment of your motorhome.

Lex Ward.