No valves, nothing fancy -- just three ports, two chambers and a passageway between them:
Here's my thoughts on how it functions. The canister is divided into two chambers, about 2/3 and 1/3 -- both filled with activated charcoal. The divider goes from the top to near the bottom but there is a gap at the bottom connecting the two chambers. The tank port and the purge valve port are side by side at the top of the main chamber. The vent port (or drain port) is at the top of the smaller chamber. There is a layer of foam rubber at the bottom that goes under the divider and allows free passage of air or fumes through the foam rubber from one chamber to the other.
When the purge valve is closed (by that I mean not drawing fumes into the engine -- low rpm, idling, not running, etc) the fumes come in from the tank, must go down thru the main chamber, under the divider, up thru the small chamber, and out the port to the long drain hose to the atmosphere. Well and good. Hopefully they get absorbed along the way. Except we know better.
Now, when the purge valve opens (higher rpm, drawing fumes into the engine), it seems the first thing it would do is draw fumes directly from the tank as the two ports are side by side. (There were filters over both those ports to prevent contamination, or anything being drawn into the engine by the vacuum. I removed the filters for the photos.) If the engine created enough vacuum, then it would start drawing air in from the vent hose in the reverse of the flow described above. Air would come up the long drain hose, down the small chamber, up the large chamber and into the purge port drawn by engine vacuum. Well and good. Except at the rate the tank generates vapor when hot, the second part of that equation may never happen. The purge vacuum may just draw vapor from the tank, maybe never even keeping up with the rate of generation, and certainly not cleansing the charcoal. So when you shut off, or the valve closes, you are defeated. The fumes pass thru the “full” charcoal and out the hose.
In my case, I am certain there was never any liquid sloshed into the canister. The charcoal was totally dry, the foam rubber totally dry with no signs of liquid anywhere. If liquid had been in that canister, I would have seen it. I had bad fumes right before the canister was removed but the canister was totally dry. In my case, I'm sure the volume of fumes just overwhelm the small canister and go out the bottom of the hose. Since the canister is warm on the 2011's and the hose is warm, the fumes do not condense inside but get pushed down the vent hose and when they hit the cold air at the bottom, they condense and cause the drips. On my 2011, the hose from the tank to the canister has a 90-degree fitting on the tank, then rises vertically at least three inches over about a foot or more of horizontal length before turning down to the canister. I personally believe that fuel would not slosh thru a 90-degree fitting and then go uphill all that distance through a small diameter hose. Now if the tank were overfilled and subject to thermal expansion, I could imagine fuel being forced into the hose but without accurate knowledge of the headspace built into the tank and the degree of expansion, I can't say if that is likely or not. In my case, I am sure that did not happen. Your situation and your opinion may be different.
Staying away from controversy, I hope this at least helps with understanding what's inside that mystical canister.
