I need really dry air to purge an FTIR just to keep the beamsplitter from ruin. The flow rate is low, on the order of a fraction of a scfm. Drierite
sells a column to dry air and it looks inexpensive, however I need a source of oil-free compressed air. What and where do you look for such a thing?gsd - 8-2-2016 at 09:11
What is the pressure required?
If it is not critical and you just need to move air around to do cooling by convection then you can try fish tank air pump.
gsdS.C. Wack - 8-2-2016 at 13:56
What about canned air? This is usually some fluoro-thingy and I can't imagine why.
There are small oilless vacuum pumps that give vacuum at one outlet and pressure at the other. The purity of this air would obviously become
questionable some place past the decimal point.JJay - 8-2-2016 at 14:40
Scuba air is oil free. You may need a scuba license to buy it, though.Dr.Bob - 8-2-2016 at 18:13
We have used a fish tank air pump for low pressures before, they are great for flask columns, as well as bubbling air through a fish tank. If you
blow one through a drying tube, it would work fine. And they can run for days, they are designed for that. IrC - 9-2-2016 at 00:34
A diaphragm type pump such as a Gast is going to be completely oil free assuming the head is clean and the input air is clean. No reason this would
not work. You could plumb it with an inline receiver dryer from an AC or Refrigeration unit. I would have a basic dust filter covering an input pipe
fed through the dryer into the pump. The output would be perfect, feeding it into a T with two needle valves would allow precise metering of the
output pressure you need with the other valve open wider to allow for steady exhaust to keep the pumps head pressure under control. I include the idea
of this added complexity since as we know the pump is just going to run at the rate it can as long as it is powered. The receiver dryer must be a new
part (not salvaged) since oil is circulated through with the freon in a working unit. Obviously it is better to use a clean new part. Or build some
kind of dryer of your own design. Of course the simple aquarium pump already mentioned may also suit your needs.
Marvin - 9-2-2016 at 01:52
I'm not aware of very dry air being needed, but if you know different for sure do say. If the unit is on and warm in a centrally heated house, that
is probably enough to prevent KBr from deliquescing anywhere outside a rain forest. If it's off and in storage you are probably best bagging it and
sealing it with desiccant inside.
I learned about this problem too late, but then the FTIR unit I have may not even be complete.ftirinih - 9-2-2016 at 10:06
The FTIR is a Bomem MB series, which are sealed and contain desiccant. Most of the models have a purge port connection, a swagelok quick connect. I
had rented a gas cylinder from AirGas but the expense was too great. I thought for a minute that the Swagelok connector required a certain PSI to
over come the spring loaded plug, but I don't think this is true. I think the mating connector releases the spring loaded plug.
The very dry air concern is one based in fear, once you ruin the beamsplitter you are done. I have been able to purchase these Bomem FTIR's for a
very reasonable price and some of them still work. I'm just trying to preserve the most vulnerable and impossible to replace part. I may have
already damaged one by leaving it in an area where it was subjected to a heating and cooling cycle, which caused it to 'breathe' in moisture.
I hadn't considered the actual 'plumbing' required to feed a controlled flow from a pump to a dryer and metering valve, I like to hear more.
I hadn't considered the actual 'plumbing' required to feed a controlled flow from a pump to a dryer and metering valve, I like to hear more.
I started the thread linked below back in 2010, study the pics of a setup I built for a bell jar to get an idea what I meant by 'plumbing', and the
use of the valves. 1/4" Cu tubing works fine and holds very high vacuum for years. I once pumped it down, closed valves, set in storage for years and
it never lost its vacuum so I assume the system is very tight. Of course you should get familiar with and skilled working with flare and compression
fittings. For the threaded junction between valve and 'T' use Teflon tape. Not so critical for your use whereas I was trying to make a vacuum tight
system. As I said this works fine for a system not requiring large diameter passages, obviously in a high vacuum system with say Turbo-molecular pumps
small diameter Cu tubing is only good for a first stage roughing pump. Off topic for your application of course. Take note in the pics of the dust
filters. If you can find these they work great and would help prevent anything from the outside getting into your optics.
A pic of a needle valve used in the way I suggested:
ftirinih - 11-2-2016 at 09:39
Thanks, I was looking on ebay for pumps and wasn't aware of the Gast products. They look inexpensive and seem to be able to blow air or pull a
vacuum.
Do you know anything about pumping down the small vacuum dewars for IR detectors? I have a few of these and wonder if they can be pumped down and
used. I know there is a special device that is used to pull the plug out of the dewar.
