Filling my on-board propane tank from a portable tank

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tantle1961

Member
Joined
Jun 25, 2018
Posts
7
Location
Washington State
We moved to an RV park recently and have not found a mobile filling service to fill my 20 gallon tank.  All the mobile services seem to have an 80-gallon minimum for those permanent installations.  It is a real pain to move my class C just to fill the tank.  I did install an adapter to use a portable 5-gallon and that works fine for a couple weeks at a time between fillings.  Before I got this portable adapter installed, I let my big tank run a little low thinking I would just call a mobile service to come out. Well, I have not found a mobile service for my area.  So, what I would like to do is take my small portable and fill just enough in my big tank for a back-up for when we run out of fuel in the small tank like we did today.  My large tank is showing almost empty but still has enough left to light the burners.  Is there an adapter that I can use to offload some of my small tank to the big one just so I won't run out?

I know this is a little long but thanks for reading.
 
Unfortunately, you can't just connect an adapter and have propane flow from one tank to the next.  You need an actual pump to transfer the liquid propane, not just the vapor you get from the normal connection.

In short, take your RV to a propane dealer and let them use their pump to fill your tank.  There's no practical or safe way to do it yourself.
 
The problem is you need more pressure to FILL the tank than the tank itself can produce.  Oh you may move a little Propane tank to tank. but to fill the tank not likely

I'd get a 20 pound portable and use it.
 
Transferring propane from one tank to another is not something I would recommend to anyone without a refrigeration license but because propane has refrigeration qualities, it is something that can be done by a qualified person. Temperature deferential between the 2 tanks is the primary factor and allows the gas to transfer as a vapor which then condenses to a liquid in the receiving tank. It is a process that must be done carefully with special attention to the amount of gas in the receiving tank which is best monitored by measuring its weight as it is filling. Over filling either one of the tanks creates an explosive condition. Using tanks of varying capacities increases the dangers.


Generally mobile filling services of propane will have a minimum. Most of these vendors will void the minimum if they can service additional accounts while they are there. Check to see if you can arrange that with other campers.   
 
The solution to your need is to add an Extend-A-Stay Tee to the propane system and simply connect an auxiliary LP bottle (a standard 20# or 30# tank) as a secondary supply. There is no need to transfer the content from one to another - simply let the second tank supply it. Turn off the valve for the main tank except when you need to remove the portable for filling.  Here's a video showing installation and use:
https://www.youtube.com/watch?v=u7fkGaktYIQ

It's not difficult to install the tee yourself. It's a low pressure fitting and requires only basic "handyman" plumbing skills.

There are several brands available:

https://www.amazon.com/Marshall-Gas-Controls-536-00-Standard/dp/B002UC4T6C
https://www.campingworld.com/stay-longer-propane-adapter-kit-82583.html
 
    tantle1961,  You can transfer propane from one tank to another without a pump, but you must have a “source tank” that is equipped with a “bottom draw” valve....to get liquid propane. You can’t get liquid propane from a typical propane bottle! The tank to be filled must have a lower pressure than the source tank, to be able to transfer without a pump. Venting the bottle is a must, to lower the tank pressure for the transfer!  As stated....caution must be taken!

    We do this all the time from our home tank, transferring to our RV tanks and propane bottles for home use. The tank to be filled must have the vent opened.....allowing a pressure drop in the “filling tank”. This pressure drop also lowers the temperatures of the filling tank, helping to further lower the “receiving” tank pressure! Obviously, the venting propane can be a explosion risk. This is normal for the filling of small propane tanks as they do not have a return line back to the supply tank.....to equalize the tank pressures. The “equalizing line” system is used with large systems (industrial) when pumping  from the source tank to the receiving tank. 
 
We have an Extend-A-Stay installed on our motorhome and use a couple of 30 lb cylinders to augment the 29 gallon onboard tank when we're stationary for awhile. The two cylinders usually last at least 4 weeks depending the weather conditions. Even longer when the furnaces are not needed. The LP supplier at our Adirondack cottage will fill the motorhome tank, but only when filling the cottage 300 gallon bulk tank. I'm looking into running a line from the bulk tank to the motorhome to use when we're there.
 
I found this video which explains how to transfer liquid propane from one cylinder to another without a pick up tube in the supply tank. In order to safely transfer propane, the principles in this video must be understood. Propane changes from a liquid to a gas at -44f at atmospheric pressure. Once the gas is pressurized. the boiling point rises. This is called pressure temperature relationship which makes the transfer of propane via gas, a liquid transfer and it is quite fast and dangerous. Propane has a very good thermal response and is why it was a popular refrigerant. The price was good too.


Enjoy the video

https://www.youtube.com/watch?v=EBFUZ7TTvHQ
 
Lou Schneider said:
Unfortunately, you can't just connect an adapter and have propane flow from one tank to the next.  You need an actual pump to transfer the liquid propane, not just the vapor you get from the normal connection.

In short, take your RV to a propane dealer and let them use their pump to fill your tank.  There's no practical or safe way to do it yourself.

Actually, it can be done without a pump using a gravity feed, if you are prepared to wait long enough. The time will vary depending on how high you can raise the full tank.

Last summer, I needed to fill two 20 lb. tanks. The only place within about 50 miles had just had their pump go out. The guy hooked up our first empty tank, and we waited about 40 minutes for it to fill. We went for lunch while the second one was filling.

Joel
 

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