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 > Any option for re-filling MH Propane Tank from Small Tank?

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time2roll

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Posted: 03/02/21 06:43pm Link  |  Quote  |  Print  |  Notify Moderator

wanderingaimlessly wrote:

I'm not a specialist on this, but a question, Since many people run a portable grill from a low pressure line run from the RV system, Why , couldn't you attach a tank with a grill regulator to one of those fittings to basically back feed the system after turning off your main tank?
You can certainly run the RV like this and save what is in the RV propane tank.
System needed is described above.


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Posted: 03/02/21 07:20pm Link  |  Quote  |  Print  |  Notify Moderator

This is my BBQ setup and shows the external tank port.

Low pressure propane fittings are common on RVs and you may need to remove the BBQ regulator as the use of 2 regulators may give inconsistent propane pressure.

This is my high pressure adapter with a El (for hose routing considerations) and a shutoff valve. The top external tank port is for additional external tank. The BBQ connector is the standard 1 lb 1" screw on propane bottle type.

[image]
[image]Click For Full-Size Image.

Hoses with the standard 1” screw on adapters are available. And an adapter for the standard BBQ regulator fitting are available. Propane stores can also make custom length hoses however I use 1 or 2 12' hoses as needed.

Here are the parts that connect to any grill with a external tank connector.
[image]


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Posted: 03/03/21 04:51am Link  |  Quote  |  Print  |  Notify Moderator

Though I have heard of tank to tank transfers they are "Discouraged"
A much better solution is called the "Extend-a-stay" This is actually a brand name of a product once made by a company (Marshall brass) my mother once did a consult for.. but alas I do not think they make it any more.. MOST RV stores if you ask for it they will take you to one of several competing nearly identical products. }

The full kit consists of a 4-way manifold that goes between the tank and the regulator. This manifold has 4 ports. The main inlet port is a POL fitting to match your RV's tank, the main outlet is either an ACME or POL to match the fitting on the regulator. The other ports are a "Quick Connect" (like the top of a disposable bottle) and an "inlet) small nut or bolt (Plug really) screwed into it .

Plus two hoses
one is a 10 foot Quick male/female for running a portable grill off the RV tank

The other is a short (5') hose Acme to that secondary inlet (the one with the plug)

Check valves insure propane only flows out the outlets and other valves only when a hose is connected to the aux-out (Same as the bottle it resembles, same kind of valve)

Had one on my Rig for 15 years used both of the Aux ports at one time or another.


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Posted: 03/03/21 05:30am Link  |  Quote  |  Print  |  Notify Moderator

MountainAir05 wrote:

wanderingaimlessly wrote:

I'm not a specialist on this, but a question, Since many people run a portable grill from a low pressure line run from the RV system, Why , couldn't you attach a tank with a grill regulator to one of those fittings to basically back feed the system after turning off your main tank?



vapor and liquid.


No, I said "after turning off your main tank"
At that point you are not attempting to fill the tank with liquid, you are supplying a vapor to the system, the same as happens when running from the main RV tank, just flowing from a different source and direction.

theoldwizard1

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Posted: 03/03/21 06:47am Link  |  Quote  |  Print  |  Notify Moderator

Quick background on LP (liquid propane).

LP (sometime called LP gas - LPG) is stored in your tank is always part liquid and part vapor (gas). The gas, and therefore the liquid, is under pressure. Some large tanks dispense liquid, but the typical tank and RVer would run into dispenses vapor.

If you hook two tanks together with a hose you will wind up with two partially filled tank as the pressure will equalize. This is why it is difficult to refill disposable bottle.

The pressure in your tank varies with temperature. If you want to transfer the LP, you need different pressures. Cool the receiving tank in an ice water bath. If not practical, heat the full tank with hot water. Placing the full tank in the sun and the receiving tank in the shade DOES WORK but it takes a long time !

A temperature difference of about 20F should give you about 20 additional psi.

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Posted: 03/03/21 07:26am Link  |  Quote  |  Print  |  Notify Moderator

Suggest you just do what is obvious and drive to the propane dealer and get the tank filled. You are going to end up with a lot of potential leaking joints, expense and trouble. Bite the bullet and get a lot more propane for a lot less risk and trouble.

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Posted: 03/03/21 07:58am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

You could add an extend-a-stay system and run from the smaller tanks.


This is the best way! Get a couple of propane cylinders you can carry to a refill station in the back of your car. Leave the MH parked.

Extend-a-stay


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Posted: 03/03/21 08:06am Link  |  Quote  |  Print  |  Notify Moderator

I'm sure if you took it in to a propane place they could retrofit a 2 way selector valve (most towed RVs have one to select from the 2 portable tanks).

Then you could connect up a BBQ tank if you can't get the MH into a filling station.

I'd look to find a propane shop that does custom hoses but it shouldn't be anything too complicated.


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Posted: 03/03/21 08:28am Link  |  Quote  |  Print  |  Notify Moderator

Many years ago I worked for the Forest Service burning logging slash piles. We used back-pack propane torches. When the torch bottle was empty, we returned to the pickup and filled the bottle from a 100 pound cylinder in the back of the truck. Liquid transferred from the big cylinder to the little bottle using only the pressure in the big cylinder. Of course, we had to open the "80% valve" on the little bottle to relieve the pressure so it would fill properly. As soon as we got liquid from the "80% valve" we shut off the valve on the big cylinder, shut off the valve on the little bottle, disconnected the hose, connected the torch and went back to lighting fires.
This long dissertation is just to illustrate that it IS possible to transfer liquid propane without a pump. Is it "safe"? Probably not. Anytime a flammable gas is vented to the atmosphere it can be dangerous.
Good luck.


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time2roll

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Posted: 03/03/21 08:30am Link  |  Quote  |  Print  |  Notify Moderator

theoldwizard1 wrote:

The pressure in your tank varies with temperature. If you want to transfer the LP, you need different pressures. Cool the receiving tank in an ice water bath. If not practical, heat the full tank with hot water.
To move liquid you would need to cool the tank to maybe -45 degrees maybe a little lower. OK it would move as a gas and condense into liquid in the very chilled tank.
Dry ice at -78F would do the trick.

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