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www.shleggitt.com site under "information page." what he said....what he said????
MGC 5th WHEEL REMOTE CYLINDER LP GAS SYSTEM
SYSTEM DESCRIPTION
WHY THE HIGH PRESSURE REGULATOR?
WHY USE THE BACKCHECK?
SYSTEM DESCRIPTION:
This system has one cylinder located on the right hand side (door side) of the trailer near the front storage area, and a second cylinder (remote cylinder) at the same location on the left hand side (off door side). Connected to the right hand cylinder’s service valve is a “Type-1“ high-pressure pigtail. The pigtail is attached to a backcheck fitting that is threaded into one inlet of the automatic changeover regulator. A hose of appropriate length is attached to the other inlet of the automatic changeover regulator and is routed across the trailer, out side of any compartments, and attaches to the outlet of a high-pressure regulator. The inlet of the high-pressure regulator has a back-check fitting threaded into its inlet and a “Type-1“ high-pressure pigtail attached to the fitting. The pigtail is then connected to the remote cylinder’s service valve.
WHY THE HIGH PRESSURE REGULATOR?
The boiling point of propane is approximately –44oF therefore if the liquid propane is colder than –44oF there will be no propane vapor pressure. As the temperature of the liquid propane starts to rise above –44oF, the liquid starts to boil, creating vapor pressure in a closed system. When the temperature of the liquid propane reaches 68oF, there will be approximately 100 pounds per square inch (psi) of vapor pressure in the system. If the liquid propane temperature reaches 90oF the vapor pressure will be approximately 165 psi. When the temperature of the propane liquid stabilizes, the boiling action stops and the propane vapor pressure also stabilizes. Now lets assume that the temperature of the liquid propane starts to decrease. As the temperature of the liquid decreases the vapor be gins to turn back into a liquid form (condense). As the condensing process continues the vapor pressure will continues to decreases. If the temperature once again stabilizes the vapor pressure will also stabilize. If we can maintain a stable temperature of the propane liquid or a stable vapor pressure there will be no condensing of the propane vapor. We cannot control the temperature of the propane liquid. We can however control the vapor pressure by installing a high-pressure regulator in the system.
If we install a high-pressure regulator, set at 30 psi, as close to the remote cylinder as practical then that part of the system that receives this pressure will prevent any condensing of the vapor. If the temperature of the propane liquid falls below the point where it can not boil off sufficient vapor to maintain 30 psi pressure, then the vapor will once again begins to condense. The liquid temperature required to maintain 30 psi vapor pressure is approximately 0oF.
WHY use back-checks?
Assume the following: that the system has no back-checks, that we have the remote cylinder selected as the service cylinder and that the remote cylinder is empty. Under this scenario that part of the system between the remote cylinder and the automatic changeover still contains ten psi vapor pressure. When the consumer disconnects the remote cylinder to get it refilled all of the vapor pressure will be discharged out of the disconnected pigtail. This situation will be prevented by use of back-checks.