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REFILLING 1 POUND PROPANE CYLINDERS

DISCLAIMER  -  The content of this article is based on the experience, research and opinions of the author.  The information in the article is not intended to replace professional advice or help.  It is recommended that readers seek the advice and help of professionals.  The author assumes no responsibility for the use or misuse of any information contained in this article.   Improper handling, transporting or storage of propane can have disastrous results including explosions that can cause property destruction, personal injury and even death.  Read and obey all manufacturer instructions.  Follow all safety rules.

16.4 oz Propane Cylinders

The most popular propane cylinders for weight and ease of transport are the 16.4 oz (usually green) single use propane cylinders.  These are the ones we associate with table top camp stoves, lanterns, and other appliances.

The best price I have found on them is at Sam’s Club where they sell for $10 for a 4 pack ($2.50 each).  Many stores sell single cylinder for $3.50 or more.

Four of these small cylinders hold the equivalent of 1 gallon of propane, which means we are paying $10 – $14 for a gallon of propane when we buy the convenient little green cylinders.  Propane is about $2.50 a gallon right now from a bulk refiller.

 

Refilling 16.4 oz Propane Cylinders

There is a great little adapter that lets you refill 1 pound cylinders from a 5 gallon bulk cylinder.  This means you can have the convenience of the small 1 pound cylinders for the cost of bulk propane.

A Propane One Pound Tank Refill Adapter sells for around $12.  They are fairly easy to use and with a little knowledge you can refill your 1 pound propane cylinder to 90% of its original fill.

Most people can only get the 1 pound cylinders to refill to about 50%.  While using half-filled cylinders makes you change cylinders more often, it still lets use cheaper bulk propane.

Why do most cylinders only refill to only 50%.  Well, it is science working against you.  But knowledge is power and we’ll make science work for us and get consistent 90% refills.

First some precautions.  Only refill 1 pound propane cylinders outside in a well ventilated area away from any ignition source.  Small amounts of propane are leaked as you connect and disconnect the 1 pound cylinders. Safety First.

You may want to wear a pair of gloves.  Liquid propane is very, very cold and as you connect and disconnect the 1 pound cylinders, you may get splashed by some very cold liquid propane.

 

Step By Step Instructions

The refill adapter comes with instructions but here is how I refill 1 pound cylinders step by step.

1.  Make sure the cylinder valve is closed.  Screw the refill adapter into a 5 gallon cylinder that is at least half full and sitting upright.  The threads that screw into the bulk cylinder are reverse threads which means they screw into the tank counter-clockwise.  Snug tight with a wrench but Do not over-tighten.

2.  Turn the bulk 5 gallon tank over on a sturdy flat surface like a table or truck tail-gate.  Orient the tank so the valve opening is toward you and accessible.

Some people wait to turn the bulk cylinder over until after they have attached the 1 pound cylinder.  But I think it is too easy to bump or bang the 1 pound cylinder when you are turning the tank over.  A good bump or bang can damage the cylinder valve, adapter, or 1 pound cylinder.

Why do we turn the bulk cylinder upside down?  Propane exist as both a liquid and a gas in the cylinder, with the liquid always at the bottom.  We want to transfer liquid propane to the 1 pound cylinder so we invert the bulk cylinder.

3.  Attach a 1 pound cylinder to the other end of the refill adapter.  The threads on the 1 pound cylinder side of the adapter are regular threads, so they tighten by turning clockwise (Righty Tighty – Lefty Loosey).  Tighten it until it is just snug.  If you tighten it past snug, you can actually unscrew the adapter from the bulk cylinder since it uses a reverse thread.

4.  Tilt the bulk cylinder back slightly so that you can open the cylinder valve, then return the bulk cylinder to a sitting flat position.  You’ll hear the propane start to move into the 1 pound cylinder.  Watch and listen for propane leaks at the adapter connections.  If you hear or see any, turn off the valve, retighten the connections and try again.

After about 1 minute of transfer, you’ll hear the transfer noise stop.  Turn off the cylinder valve and unscrew the 1 pound cylinder.  Your 1 pound cylinder will be about 50% full.

Once the transfer noise stops it doesn’t do any good to leave the valve opened and give it more time with the 1 pound cylinder attached.  No additional propane will be transferred because as I said before science is working against you.

 

What’s the Science?

What science is working against you? Why won’t the 1 pound cylinder take more propane?  It is all about heat, pressure and the amount of propane in each cylinder.

An empty cylinder has very little if any pressure.  The propane in the bulk cylinder is under pressure. When you refill a 1 pound cylinder, the pressure and temperature of the 1 pound cylinder will increase as the volume of propane increases.  The pressure and temperature in the bulk tank will decrease and the volume of propane is decreased.

At some point the pressures in the 1 pound cylinder and the bulk cylinder will equalize and transfer of propane will stop.

 

How do you make Science Work for You?

The real question is how to make more propane transfer from the bulk cylinder to the 1 pound cylinder before the pressure in the two cylinders equalize?

The volume of the bulk cylinder is 20 times that of the 1 pound cylinder.  So changes in volume, heat and pressure will affect the 1 pound cylinder much quicker than the bulk cylinder.

 

Change Pressure – The only way we can increase or decrease pressure is by increasing or decreasing Volume and Temperature.  So let’s look at how changing Volume and Temperature may help.

 

Change Volume – The volume in the 1 pound cylinder is at or near zero, that is why we are refilling it.  Increasing the volume in the bulk tank will increase pressure and can result in a higher percentage refill.  Using full or almost full bulk cylinders will help maximize the amount of propane transferred to a 1 pound cylinder.

 

 Change Temperature – The optimum situation is to have a warm bulk cylinder and a cold 1 pound cylinder.   Since we will increase the volume and pressure in the 1 pound cylinder as we refill it, having the 1 pound cylinder as cool or cold as possible when we begin refilling would help increase the volume of propane we can transfer before the 1 pound cylinder heats up to equalize with the bulk cylinder.

Lowering the temperature in an empty 1 pound cylinder is quite easy and safe.  You can simply place the empty 1 pound cylinder in the freezer for a hour before refilling it.  This will help increase the refill percentage.  This trick will work during normal conditions but in an emergency situation a freezer will most likely not be available.  As it turns out, we can get 90% refills without the time and trouble of freezing the 1 pound cylinders.

We will be removing volume, pressure and temperature from the bulk cylinder during refilling, so theoretically having the bulk tank as hot as possible when refilling begins should increase the volume of propane we can transfer to the 1 pound cylinder.

Can you see a problem with the idea of increasing the temperature of a container filled with combustible gas and liquid?  As it turns out we can get great results without increasing the temperature of the bulk cylinder, so scratch this idea off your list.

Using a hot bulk cylinder that has been heated in a baking sun could cause the 1 pound cylinder to be overfilled.  This could cause the cylinder to inject liquid propane into your appliance while you are using it and could cause a flame flare-up.  Not a good thing.  Use a warm bulk cylinder (under 90 degrees).


The Easiest and Best Fix

The best solution I have read on how to maximize your 1 pound cylinder refills is from A Primer on Propane for Prepping and Survival by Chris Newman posted at Backdoor Survival.  His suggestion is to just fill the 1 pound cylinder twice.

After the first refill, turn off the cylinder valve, unscrew the 1 pound cylinder and let both the bulk cylinder and the 1 pound cylinder sit so the temperatures of both cylinders can adjust back to normal.  Then repeat the refill steps.  This should give you an 85% to 90% full cylinder without any temperature tricks.

An 85% to 90% fill is a good level of refill, almost full but with a safety margin from being overfilled.

 

Preventing Overfill

The easiest way to make sure your 1 pound cylinders are not overfilled is to weigh them empty and then weigh them again after refilling (a shipping scale works great).  The cylinders hold a little over 16 ounces of propane.  If the weight after the first refill has increased 8 ounces, then the cylinder is half full.  Shoot for final total of 13.5 to 14.5 ounces of propane after both refills.  That is 85% to 90% full.

 

Check for Leaks

After the first and second refill, you should check for leaks from the 1 pound cylinder by putting a little soapy water solution on the cylinder.  If bubbles form, you have a leaker.  If it is a slow leaker, you can either attach it to an appliance with a closed control valve, cap it, or drain it back into the bulk cylinder.

The least expensive place that I have found cylinder caps is at Camping World.  I paid $4.39 for 2 brass caps.

 

 

Here is how to transfer propane from the 1 pound cylinder back into the bulk cylinder.  With the valve closed, attach the 1 pound cylinder to the refill adapter.  Lay the bulk cylinder on its side with the 1 pound cylinder oriented vertically upside down. Open the valve and wait until the transfer noise stops.  Shut the valve and remove the 1 pound cylinder.

Leaking 1 pound cylinders cannot be repaired and should be thrown away.

 

Be Safe.

 

 

 

Ed Rogers
Copyright “Keep It Simple” 2013. All Rights Reserved.

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