He! He! Liquid propane tanks are boring! Well … they can be BUT since you will find them on all types of RVs including motorhomes, folding motorhomes, truck trailers, travel trailers, and fifth wheels, it stands to reason that since the we are using, we should also understand them. Remember, liquid propane is a gas, it is stored under pressure, it is flammable, and it can be dangerous. Not only are there rules that must be followed in its use, but laws have also been enacted to help ensure the safe use of liquid propane. This is all especially relevant for older units and many buyers of these units who thought they “got a robbery” on that old trailer are surprised to learn that LP cylinders are “out of date” and subsequently “illegal”. .
Okay, let’s go over some basics.
First, there are two types of tanks or cylinders.
DOT (Department of Transportation)
Dept. The shipping container is the one most of us are familiar with. They are
Vertical in style and are known as DOT cylinders.
– mainly used in folding motorhomes, truck motorhomes, travel trailers,
and fifth wheels.
– can be removed from the RV
– Usually used in an upright position, BUT not always. Some can be used
horizontally, but each cylinder MUST be used in the manner to
that was designed. (they are usually marked for the position in which they should be used)
Cylinders prior to 1998 without OPD devices could be used both ways, but this does not apply
Today as OPD, devices are required on ALL ASME (American Society of Mechanical Engineers) cylinders
-manufactured to the code of the American Society of Mechanical Engineers
-more commonly known as “tanks”
-commonly found in motorhomes
-they are permanently mounted
ASME SERVICE VALVE
-marked “steam withdrawal”
-used only for steam extraction
(ASME tanks have a separate fill valve, one with the yellow cap)
TYPES OF SERVICE VALVES
Three types have been available for RVs in recent history
1) The most common was the POL CG 510 (Presto Lite)
-identified by its 5- or 6-point rotating handle and its
left handed metal hose connection
2) OPD service valve with “quick disconnect” which is mainly used
by the barbecue industry and is NOT allowed for use in RVs
Quick disconnect fittings can be used downline on RVs in such
things like gas grills but are not allowed in the liquid propane cylinder
3) Type I OPD Service Valve Now Mandatory (May 1, 2002) and
has a 1 5/16 “ACME thread and is easily distinguished by its black color
or green connector for connecting the high pressure hose.
The rotary open / close handle will also only have three prongs that
distinguishes it as the new style.
“NOTE”
However, there is an exception. You can meet the “POL style” with
left-handed brass hose connectors with OPD devices. It is easy
distinguishable as the open / close rotary handle will NOT have the old
style 5 or 6 point, but will have the new style 3 point handle that
it will be clearly labeled OPD. You can be sure that it is not only
updated but also legal.
OPD DEVICE (Overfill Prevention Device)
Okay so what is the problem with the OPD device that we have been referring to? OPD devices
Cylinders and tanks are now required on all RVs are a safety device for
make sure cylinders and tanks are not filled above the 80% level.
(OPD devices are required on ASME tanks since 1984 and DOT cylinders since 1998)
The device uses an internal float connected to the fill valve that is coupled to a piston that in
Turn restricts the flow of liquid propane to the tank once it reaches 80% of full range.
While they are not foolproof, for the most part they achieve their intended purpose. Obviously
Flotation devices differ between horizontal and vertical containers, so cylinders and tanks with
OPD devices MUST be used in the position (horizontal or vertical) for which they are designed.
MAXIMUM FIXED LIQUID LEVEL GAUGE
The fixed maximum liquid level indicator is another device that all drivers should be familiar with.
and understand its purpose. The following will help distinguish it from other devices.
-used to determine the 80% level in the container
-service valve part on DOT cylinders
-connected to a dip tube that enters the cylinder up to the 80% level -in ASME tanks it is physically at 80% full level or is equipped with an inner tube at 80% level.
How to use
-must always be OPEN (turned over) when the container is being filled
-During the filling process, steam will be emitted until the liquid reaches the
80% level when a “white mist” (liquid propane) will be emitted, which means
the container is FULL.
If the container is filled beyond this level, the excess propane must be
“purged” until only steam is emitted to ensure container is not overfilled
in addition, to warn of possible future problems with the container.
For example, an overfilled container could become dangerous if left in a vehicle
or in the sun when the temperature increases the pressure inside the tank. You now have a basic understanding of what you are looking at when you see an LP tank or cylinder and you will know if it is up to date. One more thing to keep in mind is the condition of the tank. Tanks that are rusted or missing paint should be closely inspected for any other possible damage. If you have any questions about the tank or cylinder, have it inspected by a professional.
