Remove front propane tank

[dsheets70]

The valves haven't changed over the years as far as I can see -- They are most likely to leak when they are disconnected, because that's when the valve sticks open either because of malfunction or debris in the seal.

I sometimes get leaking cannisters from folks packing up after the weekend and I just disconnect my 10# tank and put the cannister on-line with the Steak Saver -- They quit leaking when reconnected.

I purchased one of these from Harbor Freight. To be honest, I have been reluctant to use the thing because of the comments in this thread which have been brewing in my mind for a couple of months now. I still believe that there might be an external outsite use for re-charged cylendars if used carefully. I would not use them in the camper though.

[Brian B-P]

As for overfilling them, since one is pulling off of a 5 gallon tank that is only filled to 80%, overfilling the little bottle is not possible. (it's not like using a pump like used at service stations, etc. Now then it would be possible to overload the little bottles)

This makes no sense to me. The vapour and liquid in a propane bottle are in equilibrium, and that remains true regardless of the amount of vapour. It doesn't take extra pressure to completely fill, and I can't see how the the fill level of the source tank has any relevance; if everything is at the same temperature, I expect that the liquid will eventually fill up the lowest parts (the tank being filled).

Looking at it another way... how would the propane "know" to stop flowing at 80% full, or any other specific level?

I have weighed the refillable cylinders before and after refilling using the adaptor and have found that on a cool day only get about 75-80% fill (12 to 14 oz). Now on a warm Summer day, 85+ degrees, I get close to 16 oz.

I agree that weighing is the answer, but weighing only occasionally would not be goo enough for me, because the warm-day experience indicates that they can be overfilled. By the way, if the cylinder is supposed to hold 16 oz, then that's the right amount of weight to gain. From the original supplier, with 16 oz of propane in them, the appropriate free space is still left. The 80% maximum fill for safety is 80% of being solidly filled with liquid, not 80% of 16 oz. It sounds like these cylinders are usually getting filled to a very conservative level.

I assume that the temperature matters because a temperature mismatch between source and destination should produce a pressure difference, which will drive flow. The filling instruction with one of the adapters calls for chilling the cylinder, presumably to speed up filling. More chilling, faster flow, more likely to overfill...?

I check them after refilling for leakage. By doing this, I have never had one leak off on me. I think that one is safe in doing this as long as [b]all suspect cylinders are discarded. JMHO Larry

So the only check is whether it leaks immediately after filling, suggesting that the only concern is that the valve is failing. Can the valve which doesn't leak after filling at a cool temperature then leak when the temperature rises, and the pressure with it? How do we know this hasn't been happening, just not in noticeable amounts?

[Pete Dumbleton]

I assume that the temperature matters because a temperature mismatch between source and destination should produce a pressure difference, which will drive flow. The filling instruction with one of the adapters calls for chilling the cylinder, presumably to speed up filling. More chilling, faster flow, more likely to overfill...?
So the only check is whether it leaks immediately after filling, suggesting that the only concern is that the valve is failing. Can the valve which doesn't leak after filling at a cool temperature then leak when the temperature rises, and the pressure with it? How do we know this hasn't been happening, just not in noticeable amounts?

Unlike water, and like gasoline, I believe LP can expand and contract with temperature, so that may be a factor.

I think the valve leaks are due to debris in the seating, so if it doesn't leak after filling, it's not likely to leak under pressure (I would expect more pressure to make a better seal).

I've attempted to refill cannisters from my 10# OPD tank but have only had marginal success (maybe 25% fill at most, without chilling).

[Brian B-P]

All liquids expand and contract with temperature changes, but it is more noticeable with hydrocarbons (oil-based stuff) than water, and particularly with light stuff like propane. The relatively unique thing about propane compared to more familiar liquids is that it expands all the way to being a gas at "room temperature" and normal pressures; to get an open bucket of propane to stay liquid, it must be way below freezing, so instead it is stored under pressure.

Pete, how are you attempting this transfer? The only available place to attach the hose or adapter onto a bulk propane tank is a vapour port - it is on top, so no liquid comes out there. If you invert the bulk tank so liquid will flow out, I would expect the OPD float to go up, which is towards the foot of the tank and therefore open... but maybe OPDs don't work so well upside down? The bulk tank valves are also designed to limit vapour flow rate, and are not supposed to pass liquid out at all, so maybe the flow-limiting feature is a problem as well.

[Buck62]

Unlike water, and like gasoline, I believe LP can expand and contract with temperature, so that may be a factor.

Water actually expands the most... when it turns to ice.

[CD Smith]

I have reviewed the instructions on the use of this small cyclinder fill device.

It takes advantage of gravity flow of the liquid propane from the 20 lb. tank into the smaller tank. This flow will cintinue until the liguid blocks the excape of any additional vapor from the smaller tank. Therefore, if the instructions are followed correctly, the smaller tank will never overfill as the liquid will not allow all of the vapor to escape.

I only use small tanks of propane for soldering. If I used them for cooking and heating while camping, I can see no reason why I would not use this device.

[Pete Dumbleton]

"Water actually expands the most... when it turns to ice."

Actually, it expands the most when it turns to superheated steam, I believe <grinz>. But I was referring to the liquid phase of all these materials, of course!

It takes advantage of gravity flow of the liquid propane from the 20 lb. tank into the smaller tank. This flow will cintinue until the liguid blocks the excape of any additional vapor from the smaller tank. Therefore, if the instructions are followed correctly, the smaller tank will never overfill as the liquid will not allow all of the vapor to escape.

Here's a link to refill instructions, showing gravity flow, plus chilling the cannister creates greater relative pressure in the bulk tank, increasing the rate of flow:

Refill Adaptor

By following the instructions and diagram,the bulk tank is upside down and the cannister is on its side, so some vapor remains in the top part (above the fill valve) and overfill is unlikely.

Seems to me that with the OPD stuf aside, if the bulk tank is upside down and the cannister is fully right side up (using a connection hose to do this), eventually all the vapor from the lower tank will make its way up into the upper tank as gravity causes the liquid LP (L^2 P?) to flow down, potentially overfilling the cannister. I haven't yet taken a cannister apart to see if there is internal plumbing to prevent overfill.

The process can be forced by opening the overpressure valve on the cannister ('reverse' Shrader valve, pull to open) to let vapor out -- Even on it's side, opening the valve might allow the cannister to be overfilled.

Brian, I suspect you are correct in that the OPD provisions are hindering the process, but I was successful in getting some LP to transfer.

[Brian B-P]

...This flow will continue until the liquid blocks the escape of any additional vapor from the smaller tank. Therefore, if the instructions are followed correctly, the smaller tank will never overfill as the liquid will not allow all of the vapor to escape....

If you tried this with partially filled water tanks, air in the rest of the tanks, and only one hose between them, you would be very frustrated as the air flowing up the hose and water flowing down interfered with each other. If any air was trapped in the lower tank (such as by placement on the side as described by Pete), it would get compressed until the pressure of the water from the higher tank was insufficient to push any more in... but we're not talking about water or air here.

Both tanks are full of propane liquid and vapour in equilibrium - there should be no air anywhere. The vapour in the lower tank (the small cylinder being filled in this case) is propane and I see no need for it to escape... it should turn to liquid as required. Since vapour-to-liquid conversion (condensation) releases heat, it would tend to raise the temperature in the lower tank, and thus the pressure - that's probably why the pre-chilling advice. It's just the converse of the chilling effect of vapourizing propane.

I don't see any difference between the small cylinder being filled this way and a bulk tank being filled, so I don't see any limitation on overfilling, except that it will take a long time (especially if the condensation heating effect is significant) and the person doing the filling quits after a minute or so.

This has be intrigued... almost enough to try this and check... but I'm not sure it's worth buying the $20 adapter.