LP problem or not

[bsmeaton]

I would be curious why the Engineer believes there is more to it than flow - maybe he is covering his backside.

[richfaa]

This is on the 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.

[bsmeaton]

Based on the reasoning above, it would benefit all prior 2006 owners to install the high pressure regulator at the remote tank, especially in colder climates.

Maybe the right answer is not to remove the red regulator, but if you don't have one, you should install one. Probably better off to install one from Marshall Brass instead of the fu-man-chu one Kestone installed.

[richfaa]

The entire system was re designed @ 2006. The schematic of the system is also listed under the "information page" along with part numbers. I have no idea what the earlier systems look like but now you have me curious. It is curious that the only part that is not part of the Marshall design is that red 18psi regulator that is prone to leakage. He had me verify the part numbers of the entire system to insure they were as per the design spec's.. the red regulator was he only part that was not. Dsprik's system is identical to mine. Apparently there is a check valve in the earlier pigtail connectors that Marshall felt were not sufficient.

My take after talking to keystone is that the 18psi regulator falls within a RVIA spec and is more "cost effective than the 30psi regulator.

I would consult with Marshall before just adding the 30psi regulator to a earlier system.

[bsmeaton]

I would agree - also figure if it ain't broke, no reason to break it.

Interesting on the pig tails too. I do know the changeover regulator is the same between 2003 and 2007, as I bought a spare back in 2003 and its still a good spare for the new one.

[richfaa]

The 30psi regulator cost 39.95 at a local RV store. I saw it for as low as 34.95 on the internet but had to pay shipping . Went and picked it up for 39.95.

On edit...I can't stand it.. Looked at a 08 3400 couple of spots down
It is a completly different regulator. Can't tell what brand. has the red regulator can't see what value.. They changed.....

[goin2themountains]

Ok, finally had time in the daylight to really get into it, sprayed regulator with soap. Red regulator was fine, but this time, I got bubbles from where the pigtail from the tank goes into the regulator. Pulled the pigtail off, and there was no thread sealant on it. Wrapped some teflon tape on there, and no leak. Now that I have brought up all kinds of issues with the LP system, I ended up with an easy fix. However, I still am going to keep a spare low pressure regulator handy. Thanks to you all. I learned more through this process than I did know about my LP system.

[bsmeaton]

Glad you found the leak! Always discomforting to smell that smell and not know where it's coming from.

[richfaa]

The is a screen on the very bottom of the second stage of the Marshall 250 auto changeover regulator that is installed OEM on many Keystone products. I had no clue it was there till I began to learn about these systems. Among other things it will vent propane as a safety feature in the event of a pressure buildup. So we may smell propane at times but have no leaks. We also learned that it is a real good idea to check very closely for propane leaks.