Originally Posted by
DiabloScott
I'm sure you have your process down, but you're the exception. I know you know this, but the volatiles in the can evaporate until the partial pressure of the solvent in the air above the fluid is at saturation. Every time you open the can you let in some fresh air and no matter how well you close it there will be more evaporation into the unsaturated atmosphere. This is a bigger issue the larger the ratio of air to fluid. If you only glue one patch at a time, you're opening the can and refreshing the air with every patch.
I only really work with cans of vulcanizing fluid at my local co-op. Even there with the cans being constantly opened and closed, a can of fluid can last for weeks. The fluid can dry out but that usually only happens at the very bottom of the can
and when the cap is left off.
As for the saturation question, let’s assume that all the solvent is xylene. Xylene has a saturation point of 38g per cubic meter at 20°C and 68g per cubic meter at 30°C. That’s room temperautre and about 90°F. A can of fluid has a volume of 240 mL. If the can were empty, the amount of xylene above the fluid would be 0.068
miligrams. An 8 oz can weighs about 225g. Let’s assume that the xylene is about 1/3 of the weight or 75g. To just open and close the can, flush out the air over the, that works out to 1100 openings before you’d saturate the air over the fluid with that amount of xylene. And that would be at 90°F. It jumps up to about 2000 times at room temperature.
That’s also assuming a 240 mL headspace. When the can is full, the volume of that headspace is around 60 mL.
My hypothesis: If one can would do 200 patches in a single setting, you would get far fewer patches glued doing one at a time, every two weeks before the stuff was gone. Even worse if you leave the can open during the patching, and even even worse if you do it in warm weather.
I only go through a few of those little tubes per year, so cans don't make any sense for me at all.
I don’t agree. If you make sure the can is closed between uses, it’s not hard to get close to the 1000 patches per can that I worked out above. I do agree that a can is overkill for most people...it
is too easy to leave the can open. I generally use tubes of glue but last year I did a patching project for my co-op and bought a can of glue. I did about 150 patches about a year ago and have done a few patches since. The fluid is just fine even after sitting in my garage through winter and summer temperatures.