Thursday, June 9, 2011

Cruising with LPG / Propane

Here is sv Valhalla's solution to the LPG problem that so many cruisers find around the world. LPG is dangerous and you shouldn't undertake this if you have any doubts as to safety. Please read carefully and consult with others who have done this before, before undertaking the LPG transfer.

One of the problems cruising in different parts of the world is the difference in fittings for liquid petroleum gas (LPG) in either propane or butane tanks.
In the USA the standard fitting is POL (reverse thread).
In Europe and Asia there are different connectors and fittings.
On VALHALLA we find it necessary to decant the compressed liquid (propane or butane) from a 'local' tank into our vessel tanks which will fit in the custom spaces for use and storage. 
In Micronesia we found compatible fittings but only large local tanks so decanting was necessary there as well.  Prior to leaving Hawaii I had a POL to POL transfer hose fabricated at a propane supply store.
In Asia we again find large tanks (50kg) with the POL fitting ... much too large for use on the boat.  The smaller (12-14kg) tanks use a snap-on fitting, either separate or combined with a tank regulator. For these tanks a transfer hose has been fabricated as shown.  The local tank fitting (without a regulator) and shut off valve are normally available at hardware or stove stores along with reinforced hose.  I originally used clear reinforced plastic hose, as shown in the photo, but found that the gas caused the hose to become brittle.  I now use rubber hose designed for auto air conditioning.  The shut off valve is handy since as soon as the local fitting is attached to the tank the gas begins to flow.  The male POL fitting was fabricated at a machine shop using my POL-POL transfer hose fitting as a sample.
The method of transfer is to invert and elevate the local tank and have it warmed by the sun.  The vessel tank is kept in the shade and covered with a wet towel (not shown for clarity).  The temperature differential creates a pressure differential which assists the liquid transfer.
The vessel tank is hung from a hand scale to measure the weight as it is being filled.  I weighed a tank that was filled at a commercial plant and use that as the target weight.  It is important to NOT OVERFILL the tank.  The correct amount is 80% of the volume of the tank to account for expansion from a cold to hot tank.
As the tank is being filled I open the relief valve to reduce the pressure in the vessel tank and further assist in filling.  A clear vapor will be exhausted.  I do this periodically during filling and, as the tank weight approaches the target weight I look for it to 'spit' a stream of white liquid.  At this point I consider the tank to be full and close all valves.
A safety consideration in this operation is the fact that butane and propane are heavier than air and will flow 'downhill'.  Close all openings into the interior of the boat (port lights, ventilators, hatches, companionway boards, etc.) and ensure your gas detector is functioning.

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