lloyd Posted January 21, 2016 Posted January 21, 2016 Smokey,I'm with you. I've never 'vented' a vacuum system, except either to relieve the vacuum at the end of a job, or to help purge water out of the oil in my pump (and only then by opening the purge port on the pump, NOT on the vacuum pot). The cyclic method I described has worked well in the past for maintaining a specific partial vacuum, when there were volatiles in the material being treated. It's completely automatic. Turn it on. When the pump no longer cycles on for several hours, it's done. (and yeah... with some pumps, that requires a check valve downwind of the pump, or internal leakage will keep the thing cycling forever. I've also just pulled "hard vacuum" on things, and never had any deleterious results; even stars. My vacuum gear is all leftover stuff from when I was a younger man doing a lot of pure experimentation for the joy of it. About all I use my 'good' pump for now is HVAC repairs here on the ranch. In the rare times when I use the pots now, it's for vacuum-impregnating things, like some homemade transformers, or circuits I wish to keep inscrutable to prying eyes. I, personally, do not vacuum-dry my stars. I have a nice, heated, dehumidified drying closet. That does the trick just fine. Lloyd
Nessalco Posted January 21, 2016 Posted January 21, 2016 Lloyd, I've considered building a vaccuum chamber, and want to see if I correctly understand the concept behind your approach. Am I correct in thinking that by reducing the pressure in the vessel slightly, the water tends to evaporate more quickly, but without freezing. As the water evaporates its' gaseous state raises the pressure in the vessel. This kicks the pump on, which draws the vacuum back down. Cycle continues until there is no more water to evaporate. Kevin
lloyd Posted January 21, 2016 Posted January 21, 2016 (edited) Kevin,That's how it works. The proviso I raised above is that some pumps are 'leaky' when not running, and you often must utilize a check valve between the pump and the line. Lloyd Edited January 21, 2016 by lloyd
Nessalco Posted January 21, 2016 Posted January 21, 2016 Thank you. Seems pretty straightforward. Kevin
Smokey Posted January 21, 2016 Posted January 21, 2016 Smokey,I'm with you. I've never 'vented' a vacuum system, except either to relieve the vacuum at the end of a job, or to help purge water out of the oil in my pump (and only then by opening the purge port on the pump, NOT on the vacuum pot). not vacuum-dry my stars. I have a nice, heated, dehumidified drying closet. That does the trick just fine. LloydWe always used cold traps between the cabinet and pump. Could be simple Dewar filled with ice water, or salt/ice/water or acetone/dry ice or liquid nitrogen. Lab environments usually have lots of "stuff" to address issues. One handy device was someyhing you could hook up a CO2 tank and generate your own dry ice on the spot.
lloyd Posted January 21, 2016 Posted January 21, 2016 Smokey,I'd use one if my pump weren't designed to handle water, but it is. Adding a cold trap would just be one more hunk-o-hardware, that my lab doesn't already have. (I used to have a homemade 1L Dewar flask for LN2, but it got either lost or broken in one of my several moves.) Heh! You brought back a memory! I worked during Y2K remediation for the State of South Carolina, in the Department of Health and Environmental Control. We had a HUGE (must've been 250L) stainless steel Dewar for LN2 sitting out in the hallway about 50' from my office. I never could find anyone there who knew what its purpose was! The nearest testing laboratory was three floors and 300' laterally away from where I worked. LLoyd
schroedinger Posted January 21, 2016 Posted January 21, 2016 Lloyd in your system where you used to use vacuum to dry things, did you bulk dry those things down from high moisture contents or did you use it for removing trace ammounts? Be sure i compared different methods of drying the stars. Pulling a continous high vacuum was the slowest of them all. But if you measured the temperature of the stars, they cooled always down to ~4ºC and took forever to dry. Having a light air flow and only a light vacuum did result only in a light cooling (~16 at the beginning and 22º C at the end with 24ºC air entering the cell), resulted in a drying time, that was still slower then using a drying cabinet at 40ºC air temperature and a good breeze.
lloyd Posted January 21, 2016 Posted January 21, 2016 I do not remember what I did when pulling a high vacuum, but my bent would probably have been to put fully-wet stars in. I didn't do it again, because it seemed like more bother than worth. The partial vacuum method works quite well, more especially if you can warm the contents while being pulled dry. The deficit to doing it that way is that it requires that you either purchase or make a vacuum switch that's adjustable for both vacuum level and hysteresis. Neither is hard to do, especially at around 0.5 bar, but it's just one more piece of equipment that must be made and employed. Add to that the cost of such a switch if you decide to purchase it. I made mine for about $3.00 and a spare microswitch lying around, but a purchased one can run a couple of hundred dollars. As I said, it didn't impress me as worth continuing. My drying closet works perfectly, and after hundreds of batches, I can say I have no complaints. Lloyd
CaverCork Posted January 25, 2016 Posted January 25, 2016 Do not try drying liquid or viscous acetone solutions. At room temperature (23C) the mix boiled and erupted from it's containment vessel within the vacuum chamber. I was 90% certain this would happen due to the low BP, but tried it anyway. It was fascinating to watch though, so it was worth it for the entertainment value. I may try again for final drying when most of the acetone has evaporated naturally.
CaverCork Posted January 28, 2016 Posted January 28, 2016 I can report the vacuum drying method for removing the final vestiges of acetone from larger items works very well.
Arthur Posted January 28, 2016 Posted January 28, 2016 With repurposed refrigeration pumps, the big issue is pump life. Organic volatiles and water contaminate the oil that the pump expects to be circulating with the refrigerant. then either the pump rusts and seizes or the oil thins too much and the pump fails due to failing lubrication.
lloyd Posted January 28, 2016 Posted January 28, 2016 (edited) Arthur,That can be solved with diligent servicing of the pump, but refrigeration oil ain't cheap, either. The simplest way to manage the situation is to put a filter/drier ahead of the pump input. You can build your own rechargeable one, or just purchase HVAC throwaways (which don't last very long in this sort of duty). Lloyd Edited January 28, 2016 by lloyd
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