A Good Result, First time Try.

[rotrax]

I have just refilled, to 75% by weight, a Calor 3.9 kilo Propane bottle from a 15 kilo one.

I suspect a little more patience, plus better cooling of the recieving, bottle might have got a bit more in.

All in all, well pleased. 30 minutes work and a £10.00 refill.

3 Kilos of gas in, weighed on our bathroom scales. The joining pipe cast 18 quid, the 15 kilo canister was 50 quid.

Even if I cant get the last bit out it will come to £12.50 a fill.

Well pleased, at the simplicity and the cost.

 

[MontyMariner]

The joining pipe cost 18 quid

Did this come assembled or did you put it together?
A link to source(s) would be appreciated
Just noticed you're in NZ, so link probably not appropriate for me

 

[Cardinal]

Was this achieved with the aid of gravity or was the pressure of the gas in the larger container adequate?

 

[Aeolus]

My understanding is that the vapour pressure in the two cylinders equalises once the two are connected and then the liquid gas flows with gravity. This is a link to the type of connector you need https://www.gasproducts.co.uk/catalogsearch/result/?q=propane+pigtail+ST

I believe that the ST designation means 'straight through' so that there are no valves in the connector to prevent the flow.

 

[rotrax]

Did this come assembled or did you put it together?
A link to source(s) would be appreciated
Just noticed you're in NZ, so link probably not appropriate for me

I'm sometimes in NZ, currently in the UK.

It was easy. Donor (15 kilo) bottle upside down on a chair so it was above the recieving bottle. The straight through pipe was connected to both, the valves opened and liquid gas flowed immediatly. The flow slowed after five minutes and the last kilo took 25 minutes to enter the recieving bottle.

There was a long discussion on here re refilling bottles, the search function should find it.

Post #4 by Aoleus has a link.

Good luck.

 

[rotrax]

Was this achieved with the aid of gravity or was the pressure of the gas in the larger container adequate?

Gravity.

 

[ProDave]

I do this now, but I use a 47Kg cylinder as the doner making it even cheaper. We have the 47Kg cylinders for the gas hob at home (no mains gas here)

The fact it is hard to get the receiving cylinder full, dismisses any concern that if you are not careful you will over fill the receiving cylinder.

 

[vyv_cox]

I am told that once the receiver bottle, possibly Camping Gaz only, is filled to the correct net weight it will sink in water. If the bottle was in cold water this would assist the filling.

Can you confirm if this is so?

 

[Roberto]

I am told that once the receiver bottle, possibly Camping Gaz only, is filled to the correct net weight it will sink in water. If the bottle was in cold water this would assist the filling.

Can you confirm if this is so?

Camping Gaz yes. Confirmed by weighing the bottle in neutral buoyancy with regards to a new sealed one (can't remember the exact figure, it's 6.x kg for the 907 bottle).
To speed up a little, donor bottle wrapped in black garbage bag and exposed to the sun, receiving bottle in coldish tap water.

 

[FairweatherDave]

It seems Rotrax and I were doing almost exactly the same thing yesterday . Finally my 4.5kg butane cylinder needed a refill and I could use the pipe and connectors I bought in March. I must have spent hours over the years reading the old threads. And I have just done another read. My question is on the concept of overfill. Some state it is hard to overfill, others that you should target about 80% - but then the waters get murky. 80% of what? 80% of 4.5kg in my cylinder, or do calor only refill up to 80% (with 4.5kg being the net weight they sell). To put it another way, I have refilled my 4.5kg cylinder and got it to the same weight of gas as my spare cylinder refilled by calor themselves (I have allowed for the different tare weights of the cylinders). Is one cylinder more dangerous than the other?

 

[Mister E]

With the bottle empty weigh it them write the weight on it in permanent marker or paint.
You then add to that the weight of gas you want in there, so 4.25 kilos would be a good compromise.
This gives you the total weight you want.

 

[Bodach na mara]

Exploring the gravity versus pressure a wee bit, it is instructive to consider trying to transfer water from one container to another by connecting them with a single tube in a closed system. As in the gas transfer system, one bottle is above the other and the tube runs between the top of the lower bottle and the bottom of the upper one. That will involve the upper bottle probably being inverted.
If the connecting tube is very wide, water may flow under gravity and empty the top tank, but with a narrow tube the system will become airlocked. It is necessary to allow air to escape from the lower bottle and for air to enter the upper one. Now in the system we are discussing the water is replaced by liquid "gas" and the air by gas.

It would be stupid and probably criminally dangerous to vent the gas as I described for the air. Instead the gas must be "removed " from the lower bottle by condensing it into liquid and in the upper bottle some liquid must evaporate to gas (actually vapour but I don't want to spend the next hour trying to explain the difference.) The problem is the latent heat involved. The top bottle requires heat added or it gets cold, which reduces the vapour pressure and the opposite happens in the lower receiving bottle. So if and only if you can gently heat the top bottle and cool the lower one the flow will continue, now driven by the small difference between the vapour pressures and will continue even if they are on the same level. Gravity will play no further part. The receiving bottle can be upright or inverted but the donor bottle must still have the tube coming from its lowest extremity.

 

[Roberto]

It is also advisable not to keep the donor bottle perfectly vertical, but keep it with a little tilt: there may be small impurities inside the bottle, they would remain on the side of the top (now bottom) of the donor bottle instead of going through all the pipework

 

[FairweatherDave]

With the bottle empty weigh it them write the weight on it in permanent marker or paint.
You then add to that the weight of gas you want in there, so 4.25 kilos would be a good compromise.
This gives you the total weight you want.

Thanks Mister E. That still illustrates my question. 4.25kg is 95% of 4.5kg. So are you just allowing for variation in scales accuracy and a small safety margin, or is there a difference between one I have refilled and one calor has refilled? ie a reason why there shou;ld be a safety margin beyond scales variation.. I agree with you having a target figure on the side of the bottle is a pragmatic solution.

 

[Mister E]

The 4.25 was just a figure to make life easy. If you are fed up of drinking tea waiting just stop filling when you want.
It does not really matter if the bottle is classed as full, your not selling the thing.

 

[vyv_cox]

The 4.25 was just a figure to make life easy. If you are fed up of drinking tea waiting just stop filling when you want.
It does not really matter if the bottle is classed as full, your not selling the thing.

I have seen video of stoves operating on 100% full bottles, with liquid burning at the jets. The flames were a metre high.

 

[FairweatherDave]

I have seen video of stoves operating on 100% full bottles, with liquid burning at the jets. The flames were a metre high.

Exactly my question vyv. Definition of 100% full. If calor are selling cylinders of gas, their definition of full (to a customer) will have a safety margin. Surely?

 

[lumphammer]

I've done this with a 15Kg donor and both 4.5 and 907 recipients. I put the target bottle in a bucket of water and have found that with both by the time they settle on the bottom they are just under full i.e. with the right amount of LPG not full to the top. The water in the bucket keeps the target cool, and if the water is up to the lip of the bucket then as ithe target fills water can be seen overflowing giving an indication that a transfer is taking place. I also check weigh the cylinder during the transfer to make sure it is not overflowing using a luggage scale.
So far from my 15Kg bottle I have filled 1 empty 4.5Kg and 2 907's with a top up of a partly used 4.5kg bottle, I have about 2.5Kg left in the donor bottle.

 

[rotrax]

I'll try the bucket of water trick next time, plus the black binbag and sunshine if conditions are right.

 

[northwind]

I have seen video of stoves operating on 100% full bottles, with liquid burning at the jets. The flames were a metre high.

Surely that is a failed regulator, not the amount of gas in the bottle?