It’s all about energy. Energy is when a physical change in the properties of a substance has the ability to do some kind of work. Burning gasoline in an engine results in movement, for example. Burning fuel is a conversion to heat for cooking or steam power and so on.
For over 100 years, the RV lifestyle has been about bringing home-like convenience and shelter along for the journey. Naturally, lighting, heating, refrigeration and plumbing have been what separates an RV from, say, a tent. And, as time has progressed and technology advanced, RVs have adopted many new ways of making life on the road more comfortable, but the one that has really stayed with us is LP, or propane gas. With it, we heat our RVs and our water, cook our meals and power some great outdoor appliances. Heck, some RVs even have propane powered generators, which then power up all of our modern electrical loads and charge our batteries.
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Since so many of us own RVs with propane gas systems, we should know what this energy source is all about and be ready for the long play with LP.
What is propane?
Propane is one in a family of liquid petroleum gasses produced during natural gas and petroleum refining processes. In the United States, LP and propane are used interchangeably, but most retailers market the product as “propane,” so we use that term most of the time in RV land.
Propane is an ideal fuel for RV and outdoor use. It is non-polluting, clean burning, and in its natural state, colorless, odorless and tasteless. An odorant, methyl-mercaptan, is added for safety. Propane gas is heavier than air, and changes from a liquid to a gas at -44°F. The liquid is lighter than water, and therefore would float on top of it were the conditions correct. Because the boiling point is so low compared to water, it can freeze your skin on contact. In a liquid form, propane weighs 4.24 pounds per gallon. Pressurized, propane can be transported as a liquid.
Why do you need to know these facts?
1. Skin exposure to propane gas being released from a cylinder or tank can cause a severe injury.
2. Since propane is heavier than air, it collects in low spots, or at the floor. That’s why your RVs LP gas detector is close to the floor. To vent propane out of an RV, it has to be released at a low level, and if an ignition source is at a low level, it can flash back to the source. Did you know that it’s possible to pour propane gas from one beaker to another?
3. Propane’s pressurized liquid state makes it easy and efficient to transport.
4. As the outside conditions get colder, and elevation increases, propane’s vapor pressure changes, reducing the amount of BTU’s available per gallon. This is what leads to propane fade in the mountain west and during severe winter conditions.
For more information on the properties of propane, visit https://www.propane101.com/aboutpropane.htm
Propane Containers
In RV land, propane is transported in two types of vessels: DOT cylinders and ASME tanks, named for the regulations under which they are described and maintained.
DOT cylinders are on most trailers and even some motorhomes, not to mention our propane grills at home. These (mostly vertical) cylinders have a valve on top which releases propane vapor. Regulated by the Department of Transportation, cylinders range from tiny disposable appliance canisters up to 200-gallon stationary models. RVs usually use 20 or 30 pound cylinders. Using rounding, 20lb cylinders carry 5-gallons of liquid propane, and 30lb about 7.5-gallons.
DOT cylinders must be secured for transport and have a 10-year life expectancy unless recertified, from the date of manufacture, stamped on the cylinder’s collar.
ASME tanks are horizontal, built-in propane tanks designed for vehicle use. Most propane equipped motorhomes utilize ASME vapor release tanks of various sizes. Regulated by the American Society of Mechanical Engineers, motorhome tanks do not have an expiration date, and therefore do not require recertification.
All propane vessels must be properly maintained, including removing rust and repainting as needed. Any damage to a vessel must be inspected by a propane professional.
For more information on RV propane containers, visit https://www.mantank.com/products/rv-propane-containers-accessories/
Propane piping and hoses
Now you have to get that pressurized gas to where it can become energy, and that’s through plumbing and regulators. For RV and appliance use, propane is reduced from bottle pressure to 11 inches of water column, which is read by a manometer. This controlling of the flow of gas results in a predetermined release at the consumer end (appliance) of the system. The release is measured in BTUs or British Thermal Units.
Propane plumbing, governed by NFPA 1192 for RVs, is divided into high- and low-pressure sides. High pressure from the container to the regulator, and low for the remainder of the system. Historically, RVs had high pressure copper or rubber plumbing from the container valve to the regulator, which was then connected to a cast iron pipe under the RV. That, in turn, would transition to copper inside the RV. Modern systems will often use high pressure rated rubber hose throughout much of the low-pressure side of the system. The high-pressure pigtails used between the DOT cylinders and the regulator are fitted with an Acme fitting, which is easy to attach and prevents propane from flowing unless a proper connection is made.
RVs equipped with DOT cylinders will usually have an automatic switchover regulator, With it, both connected cylinders are left in the open position. When one cylinder is exhausted, the regulator begins drawing from the full one, and an indicator will show red. The lever on the regulator is switched to the full side, and the empty can be removed and replaced while the other cylinder continues to feed the system uninterrupted.
ASME tanks on motorhomes connect using the older style POL valve fitting, which is usually directly connected to the regulator.
Appliances
Propane powered appliances in RVs will often have some type of gas regulation built in, whether it’s a full regulator, a flow orifice or both. These meter the exact amount of gas flow to reach the desired effect. Because natural gas and propane are such different gasses, often orifices must be changed to switch a basic appliance from one gas to another, but not all appliances and devices can be changed.
The RV PHD Newsletter is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.
