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Old 03-11-2013, 10:49 PM   #15
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1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,592
1.Sometimes in very cold weather, the liquid propane will freeze solid in the bottom of the tank and you can't get it to liquify, so the pressure drops and the regulator changes over to the other tank. When it warms up, there may be a small amount of propane left in the tank which froze. Otherwise, the tank should be pretty empty when the changeover takes place.
2. No
3. When the tank warms up, the liquid expands and will over pressure the tank, forcing the overpressure valve to pop off. It is not fun to have a tank on the front of your trailer spewing propane to relieve the pressure. Trust me on that one, I had an idiot overfill one of my tanks once.
4. The tank leaks propane when overfilled (see above). The regulator will not allow liquid propane into the main lines (thank goodness, the pressure would be very high and very dangerous).

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Old 03-11-2013, 11:28 PM   #16
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1973 23' Safari
Reese , Michigan
Join Date: Jan 2013
Posts: 42
propane tanks

All the info seems correct and very informational, the reason opd's were introduced was to help tanks get refilled to the correct level, overfilling was great cause for concern, not enough empty space at the top of the tank would cause pressure to raise to levels that caused the pressure relief valve to vent the excess pressure out into the air, NEVER a good thing if open flame were nearby. One correction to mention is a propane tank will always empty itself, it is a liquid under pressure in the tank and gasses off as vapor to be used by your trailers equipment as needed, so there is no pipe to the bottom, like your garden sprayer has. One note- I have heard of tanks not delivering propane after being refilled, it seems the float inside the tank may prevent the flow of gas out, and maybe a little shake of the tank will get things going again, there is also the valve at the connection that may not open if not tight enough. Love the info available here. Gene

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Old 03-12-2013, 06:56 AM   #17
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1967 30' Sovereign
Los Lunas , New Mexico
Join Date: Jan 2004
Posts: 6,334
Actually, it's kind of an interesting story here.

OPDs were first mandated by the National Fire Protection Association (Pub 58). States were free to adopt that standard or not. Most did. Manufacturers of cylinders immediately adopted it.

But what about filling? If you look at the publication, certified fillers were never supposed to fill by relying on the OPD valve. Rather, the only two methods ever permitted in the publication were volume or weight: Volume by opening the small screw at the side, and weight by using a repeatedly certified scale. And that makes sense: Fillers were to rely on gravity, which is always there, or on a certified scale, but not on a valve installed who-knows-when and never checked again. (Again, the standards in the publication are voluntary in the sense that individual states are free to adopt them in whole, in part, or not at all.)

So why the OPD at all? Pretty simple. There are lots of folks who fill at home, and those folks were doing a lot of overfilling in the false belief that an overfilled tank was a safe tank. Not!


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