LP System Know-How

Liquid Propane, or LP, is a very versatile fuel source and the lifeblood of most RV appliances. As an RV owner, it’s important that you understand the fundamentals of how an LP system works.

That knowledge will help you keep your appliances running smoothly and operating your rig in a safe manner along the way.

LP is 270 times more compact as a liquid than as a gas, making it a preferred choice for an RV fuel source as it is more economical to store and transport. In the RV application, trailers use containers known as DOT cylinders, which are upright containers like the type used in residential grills and come in small 20 lb. cylinders up to 40 lb. used in 5th wheel trailers.

Motorhomes typically use ASME tanks permanently mounted to the frame in a vented compartment – however some models recently have been using the DOT cylinders in compartments to make it easier to disconnect and refill without needing to take the motorhome to the propane distributor.

In this class, you’ll learn how LP was discovered in 1910 by a chemist in Pittsburg, how to properly fill an LP container, and how the LP system works in your RV.

In an RV, LP is used as a fuel source for the water heater, refrigerator, stove top, oven, and furnace. LP is stored in the DOT cylinder or ASME tank as a liquid and when the appliance calls for fuel, it turns to a high-pressure gas. The regulator controls the pressure as it exits and reduces it to a safe level for the hoses, valves, and appliances. This pressure is measured as water column pressure, and is typically 11 inches of water column in an RV.

Troubleshooting an LP appliance issue is easy with an understanding of how each appliance works on each mode of operation. Some appliances, like the refrigerator and some water heaters, work with either 120-volt power or LP. If the appliance does not work on the LP mode, verifying the 120-volt operation will help identify the trouble is in the LP operation and not the appliance in general.

In addition to the detailed video instruction you’ll receive, this class provides you with some downloadable resources and helpful information, including: A detailed Class Guide you can follow and use as a reminder for the key points of the class instruction; and five resource documents that will help you with various aspects of safely using LP gas.

Class Materials:

Session 1: History of Propane

This opening session will provide you with a little history of Liquid Propane (LP). In 1910, a chemist discovered propane during an investigation of why gasoline was evaporating at such a high rate. Using a still, he collected the vapors and found propane, butane, and other hydrocarbons. Soon after that the propane industry was launched. 1912 saw the first propane oven, 1913 saw the first propane powered vehicle, and by 1927 propane sales reached over 1 million gallons. Today, propane is a $8 billion industry!

Session 2: Overview of LP Tanks and Cylinders

LP is stored in a liquid state in containers known as DOT cylinders in trailers, and ASME Tanks in motorhomes. DOT cylinders are portable like those used for residential grills and can be removed and taken to the filling station. They need to be certified after 10 years. ASME tanks are permanently mounted to the frame of a motorhome in a vented compartment.

Session 3: Overview of LP System

This session will give you a run-down of how an LP system works with various appliances in your rig. LP gas is compressed by approximately 270 times by volume to create a liquefied form for convenient storage in containers. Therefore, the DOT cylinders and ASME tanks are made of heavy steel to withstand the pressure.

When the container valve is open and an appliance calls for fuel, the liquefied gas turns to vapor and passes through a regulator that adjusts the pressure to the specifications for the hoses, valves, and appliances. Once the valve is open, the LP vapor is available at the line to the appliance.

Session 4: Checking LP Levels

There is quite a bit of campground fiction regarding how to test the level of LP in your container. Some include using IR heat guns, weight gauges, and even a construction stud finder. All these methods are put to the test and facts are presented.

Session 5: Overfill Prevention Device (OPD)

The Overfill Prevention Device or OPD is a valve inside the container that restricts the filling of the tank to approximately 80% to allow for expansion of the LP. As of January 1, 2003 all containers of LP are required to have an OPD valve. A distinctive triangle handle on DOT cylinders indicate the proper valve.

Session 6: Proper LP Filling of DOT Cylinder

Filling a DOT cylinder is not a DIY job and must be performed at a certified LP filling station. You need to make sure they are certified and familiar with your type of system. Your job is to educate yourself on the proper procedure and make sure the procedure is correct. This session will help you gain that knowledge.

Session 7: Proper LP Filling of ASME Tank

To properly fill an ASME tank that is permanently mounted to a motorhome chassis, you’ll need to bring your rig to a certified propane distributor. Even with that, there are safety steps you need to keep in mind. All appliances with a flame, pilot, or spark attempt must be shut off. All people and pets must be out of the rig and away from the filling process. This session will walk you through the safety considerations and the filling process.

Session 8: LP Regulators

LP in the container is in a liquid form, as the appliance calls for fuel, it turns to a high-pressure gas and the LP regulator reduces the pressure to a safe level. Larger systems with various appliances require more fuel and need a 2-stage regulator.

Session 9: Excess Flow Valve

All RV LP systems have an excess flow valve that senses an abnormal flow rate, such as a broken hose or loose connection. This spring-loaded valve shuts of the flow of LP in the case of emergency but can also close if the valve is opened to quickly.

Session 10: LP Leak Detection

LP is heavier than air, therefore if a leak develops in a line or fitting, it will settle lower to the floor. An LP Leak Detector is installed lower in rigs per RVIA code and will detect the compound and emit a warning.

Session 11: Troubleshooting LP Appliances

Troubleshooting starts with an understanding of how the appliances works as some operate on either 120-volt power or LP, and both methods require 12-volt DC power as well. Then a systematic approach starting with proper LP pressure, voltage to the appliance, and other operations.

Session 12: Troubleshooting LP Refrigerator

An absorption refrigerator can run on either LP or 120-volt power, however both operations require 12-volt DC power for the inside monitor panel to function. Verifying proper operation on both 120-volt and 12-volt is the first step in troubleshooting to pinpoint whether the trouble is in the LP mode or the refrigerator itself.

Session 13: Traveling with Propane

Although not illegal, it’s not a good idea to travel with the propane system open and an appliance on. If you do, make sure you shut off all flame and spark sources before entering a fueling station! See a tip on how to keep your refrigerator cold while traveling with the propane system shut off.

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