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LP Gas System Tips & Hints

December 6, 2019

The gas used in RV’s is stored in a liquid form. It is the vapor from propane that burns. It is heavier than air. (Which is why leak detectors are located near the floor). Propane is colorless, during manufacturing it is “odorized” for easy detection. Approximately 91,500 BTU are contained in one gallon of LP.

Storage Vessels

There are two methods of storing LP on RV’s: Department of Transportation (DOT) cylinders are typically mounted on the front of trailers. In fifth wheel units and in truck campers, it is found in exterior compartments. The most common size used on RV’s are the 20 and 30 pound tanks. These tanks must be re-certified every twelve years. The latest generation DOT tanks are fitted with quick closing coupling (QCC) valves, which have three safety features. If you open the service valve without having a fitting and hose properly attached, there will be no gas flow. It also has a fuse that will shut off the flow of gas if the valve gets hot in case of a fire (while in use). If the pigtail should break, the flow will automatically be restricted. DOT tank outlet valves have left-handed-thread connection known as the POL connector. The other type of tank is American Society of Mechanical Engineers (ASME), are in a horizontal configuration that is used almost exclusively on motorhomes. They have a separate port for filling, and are designed to be bolted to the RV’s frame. They must be filled in place. They do not require re-certification but when the label rusts off, the tank must be replaced.


The appliances in an RV are designed to operate at a lower pressure level. The regulator is designed to reduce the high tank pressure (150 psi full) to a steady 11 inches water column, about 0.4 psi. Two stage regulators are actually two regulators in one. The first stage reduces the pressure to about 10-15 psi, the second stage is needed to further reduce it to the 11 inches of water column. Regulators are not repairable. Open the valve slowly, quickly opening the valve can be hard on the regulator diaphragm. The regulator vent is covered with a fine mesh screen. It should be checked and cleaned regularly. Even a small blockage could cause enough of a pressure drop to allow the pilot to blow out.

Automatic Regulators

These are typically, used on travel trailers, fifth wheel and pick-up campers when the pressure is too high then pig-tails are used. Both tanks are left on at the same time, the regulator uses the “service” tank as indicated by a mark on a knob or lever. When the service tank is empty, the regulator automatically switches to the other tank and an indicator pops up indicating it is empty.
Stop Fill Valves – the ASME (motorhome) tank use stop-fill valves, which automatically stop the filling process when the tanks are 80% full. Stop-fill valves operate like a float mechanism on a household toilet. The float is pushed up by the rising liquid in the tank. The float then exerts enough pressure on the valve to stop the flow of gas.

POL Fittings

These are special fittings that are used to hook pigtails to the tank. The POL have left -hand threads, and are a high pressure fitting. When re-filling the tanks inspect the POL making sure there are NO NICKS OR SCRATCHES, which could make a poor seal which could result in a leak. Current code calls for brass on brass seal. Check for leaks with soapy water. Never use soap with harsh chemicals. These can corrode the lines and fittings.

Propane tanks can be filled at an LP gas service facility. It is not a self-service operation. Safety Certified Professionals should fill LP tanks.

Leak Detectors

Propane is heavier than air and will seek the lowest level. Therefore units with electronic leak detectors have the sensors near the floor. When gas is detected they sound an alarm. On some RVs a tank mounted solenoid shutoff valve immediately shuts off gas flow when the alarm is activated.

The supply of LP in your tank will be used according to the size (BTUs) that your appliances have and how often they are used.