How much refrigerant is left unutilized in exhausted 30 lbs cylinder?

[dumnut]

Those referring to expansion rates from liquid to vapor at atmospheric pressure have misread the OP's question. He asked how much vapor was left in a cylinder which is at a system's low side pressure after charging.

For R22, a typical low side pressure for an A/C unit would be about 75 psig.

I still can’t come close to your number.

See this chart and go to the 70F line. That line says that at 135 psia (121 psig) 75 lbs of liquid volume will convert to .4027 lbs (6.4 oz) of vapor at the same volume. So even if a 30 lbs cylinder was capable of holding 75 lbs of liquid, the vapor in that cylinder would only be 6.4 ounces, and that is at 121 psig.

Am I looking at this wrong? I just want to figure it out, and I don’t know where you are getting your density @ pressure numbers from?

[ICanHas]

I suppose it's too much to be considered "de minimis" per the EPA?

Even if it wasn't, with the current cost of HCFC and CFC refrigerants, why would you waste it if its recoverable?

[ICanHas]

I still can’t come close to your number.

See this chart and go to the 70F line. That line says that at 135 psia (121 psig) 75 lbs of liquid volume will convert to .4027 lbs (6.4 oz) of vapor at the same volume. So even if a 30 lbs cylinder was capable of holding 75 lbs of liquid, the vapor in that cylinder would only be 6.4 ounces, and that is at 121 psig.

Am I looking at this wrong? I just want to figure it out, and I don’t know where you are getting your density @ pressure numbers from?

I'm looking at the chart for 75F. It says the
75.00 147 psia 0.3726 cubes per pound

So, it looks to me that at 75F, it will hold 133 psig or so before there's any condensing.

My interpretation is that at 75F and 147psia with no liquid left, the vapor phase R22 weighs 2.68 lbs per cf of internal volume.

If it's only at 75 psi at 75F, its well below the vapor pressure and should behave like normal gas like air until its cooled enough that some starts to condense.

[ICanHas]

There's about a 1/2 pound left, or sometimes 3/4 lb. as icemeister says. That's easy enough to see by weighing the bottle before recovering the vapor and then after punching the hole in it so the recycler will take it.

Even at atmospheric pressure, the refrigerant within the tank has weight.

Air at atmospheric pressure shows the tare weight of steel as there is zero buoyancy when the internal contents and external atmosphere has zero density difference.

If it's evacuated, the tank produces a buoyancy comparable to a helium balloon of the same volume.

[dumnut]

My interpretation is that at 75F and 147psia with no liquid left, the vapor phase R22 weighs 2.68 lbs per cf of internal volume.

I believe you are right. I am misreading that line as weight when it is referring to volume.

Well, I learned something. I am amazed at how much refrigerant is left in a bottle. I just wouldn’t have thought it to be that much.

[ckartson]

Many times I leave my reclaimer out then reclaim the refrigerant into the system and I can dispose of the bottle on the sight. Works great!

[icemeister]

I lost my notes for my estimate of 12.5 oz, so I did it again and this time I was a bit less at 11.1 oz. (Don't know what I did different, but that's what I got today.)

(1) define the givens and the assumptions:

• Standard 30 lb R22 cylinder (Assuming 80% full of liquid when new)
• Starting at 75 psig & 80ºF (Typical condition after emptying for an A/C)
• Recover to 15" Hg (Practical lower limit for recovery)

Get some data from ASHRAE Thermodynamic Properties of R22:

(Note that the tables use absolute pressures, so I'll be using 90 psia (75 psig) and 7.5 psia (15" hg) .)

• Saturated Liquid Specific Volume @ 80ºF = 0.0135 cu ft/lb
• Superheated Vapor Specific Volume @ 90 psia & 80ºF = 0.673 cu ft/lb
• Superheated Vapor Specific Volume @ 7.5 psia & 80ºF = 8.86 cu ft/lb

(2) Estimate the actual volume of the cylinder:

• Volume = (0.0135 cu ft/lb x 30 lb) / .80 = 0.50625 cu ft

(3) Calculate the starting and ending weights:

• At 90 psia: Weight = 0.50625 cu ft / 0.673 cu ft/lb = 0.7522 lb >> 12.0 oz
• At 7.5 psia: Weight = 0.50625 cu ft/ 8.86 cu ft/lb = 0 0571 lb >> .91 oz

So the difference is actually just over 11 ounces.

[ICanHas]

Since gas fills the entire volume of container, I need to figure out the water capacity of the tank.

I think I can pull down to 25m torrs, weigh it, then let it fill up with air and weigh again..or suck it up full of water and weigh.

It looks like air weighs 1.28g per liter and my analytical balance would resolve to 0.01g, so I think I can get a fairly accurate measurement...

Then I just have to calculate whatever the vapor density is at 90psia (75pisg) for HCFC-22 and CFC-12.

How illegal would it be to say take 15 cylinders that's down to 75psi and consolidate them into one using the recovery machine?

I know refilling disposable cylinders isn't exactly kosher, but then you can buy this attachment at Harbor Freight for filling 1 lb propane bottle from barbecue tank.

As long as you're reasonable with it and don't let it sit around for ten years I don't see a big danger in it.


The real question is, when they say "net weight 30 lbs" how much of the 30 lbs is usable? I've read that on tooth paste and such, the net weight only accounts for what you can push out. So, if you were to weigh a new toothpaste, empty, cut, wash, rinse and reweigh, the difference is more than net weight stated.

When R12 is at what it costs now, there's no sense in not recovering what you can.

I suppose you could even chill one of the empty cylinders on dry ice, then suck in the contents from other cylinders so as not to introduce nastiness from contamination in recovery equipment.

From icemeister's calculation, you're looking at about one full small can of refrigerant.

I know that R22 and R12 cylinders look the same size but R22 is 1.21(11.26 liter @ 20C full) and R12 is 1.33(10.25 liter @ 20C full) specific gravity, so, if they're indeed the same tank physically, "how full" depends on each refrigerant. finding the water capacity of the tank would be useful.

[garyed]

I have 0 left in my cylinders.
When my can goes near empty I just close the high side port & let the system pump down. It will suck every drop out of the can.

[icemeister]

Since gas fills the entire volume of container, I need to figure out the water capacity of the tank.

I think I can pull down to 25m torrs, weigh it, then let it fill up with air and weigh again..or suck it up full of water and weigh.

It looks like air weighs 1.28g per liter and my analytical balance would resolve to 0.01g, so I think I can get a fairly accurate measurement...

You really don't need to do all that. I used the concept of calculating the volume of 30 lbs of R22 liquid and divided it by 80%...which is roughly how much the tanks are filled with liquid.

Then I just have to calculate whatever the vapor density is at 90psia (75pisg) for HCFC-22 and CFC-12.

I did that from the ASHRAE tables. See my calculations.

How illegal would it be to say take 15 cylinders that's down to 75psi and consolidate them into one using the recovery machine?

It's all virgin refrigerant, so there's no EPA issues with recovering and selling it, as long as you don't mix it with some used gas.

The real question is, when they say "net weight 30 lbs" how much of the 30 lbs is usable? I've read that on tooth paste and such, the net weight only accounts for what you can push out. So, if you were to weigh a new toothpaste, empty, cut, wash, rinse and reweigh, the difference is more than net weight stated.

Net weight is what is actually in the tank. How low you recover determines how much you can get out. My calcs show that recovery to 15" Hg left less than an ounce.

[mark beiser]

I have 0 left in my cylinders.
When my can goes near empty I just close the high side port & let the system pump down. It will suck every drop out of the can.

That, or save them for when you do a repair that requires evacuating the system.
Break the vacuum with the refrigerant from the "empty" jug.

Obviously it isn't practical to roll around with a bunch of near empty jugs though.

[anthonyac1]

if the unit has a high side king valve i close it and pump the unit down as i leave the tank open and let the compressor suck it out of the jug. But i dont recommend letting the compressor to run long in a vacuum. once your down to about 10 or 5 psig you got most of it. just something i do.

[ICanHas]

It's all virgin refrigerant, so there's no EPA issues with recovering and selling it, as long as you don't mix it with some used gas.

It was concerning consolidating multiple near empty cylinders into one green disposable cylinders. According to DOT, it's unlawful to transport refilled cylinders. .