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Posted: 7/31/2008 5:14:13 PM EDT
| Anyone know where the purge port is on the AVS-9. Looked high and low but don't see it. I know my eyes are not what they used to be but I have really looked all over. Hate to ask a stupid question but I just can't find the darn thing. |
| Looking from the back (just like how you would use it). Above EACH tube housing, there are 2 screw on the left and right side tuck near the pivot adjustment shelf. Make sure you use the right size screwdriver, they can be easily stripped. There are total of 4 purge screws per AVS-9 system. |
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It's a port where you would displace ambient air with inert gas. The purpose is to drive ambient air out and replace it with inert gas, such as Nitrogen. Ambient air contains water vapor (humidity)....so if the temperature/pressure change, the inside of the NVG can fog up. So you would drive fresh air out whether use suction first, and drive inert gas in.....or in the case of AVS 9, open both ports, drive inert gas in and let ambient air out the other port.....then screw it tight to seal the purge. This is the same concept as most riflescopes and binoculars do. You will see that they'll say "Nitrogen filled/purged" or whatever they're using. |
I know Argon is used. Nitrogen is the most common. I heard helium is bad for the indium seals in the tube. Now ,Im not an engineer and have no first hand experiance but thats what I heard. Indium seals are used in some really harsh enviroments and the things are tough as hell. I would not risk my tube on helium unless someone here knows for sure 100%. Helium is inert but whether or not it will damge the tube is for someone smarter than me.
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Argon is used in alot of quality optics. Many day scopes are purged with Argon. Its not common in NV scopes but a few people I know use it. It costs more then Nitrogen which is probably why its not used more often. Alot of your wine preserving canisters which can be adapted for purging scopes are a mix of Argon and Nitrogen. I have never heard of Argon having any ill effects. I heard that helium is not good as stated above but I am not sure of that. I would like to know because helium tanks are sold at Walmart and easy to obtain. It would be nice if it could be used. 
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 Does anyone know where I can get just the grey backing plate. My mount is fine but the backing plate is toast. FYI: Loctite won't hurt the plastic in the mount but it will destroy the grey stuff. (Its a sore subject so please don't ask how I know) I will get over it. Anyhow if someone has one they wish to part with I would gladly buy it from you. Leaving tmro for a trip for a few days so just shoot me an IM and I will holler at you when I return.
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Nitrogen is used by the military, I've never heard of Argon being used. The reason Nitrogen is used is because it doesn't contract and expand with temperature changes, thus the goggles don't "breath", hence, they don't draw in moisture. Notice green valve stem caps on tires now? Same reason, the tires don't change pressure with temperature changes. |
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XT optical design is an advanced optical element configuration that virtually eliminates aberrations and provides distortion-free, flat field images with unmatched edge-to-edge accuracy and detail. Excels in the roughest cover. Just like you. Not only is the Razor built to withstand avid use in tough terrain, the argon gas guarantees waterproof, shockproof, and fog proof performance. This advanced process protects your Razor binocular in the following ways: Argon gas does not absorb or react chemically with water. Argon gas eliminates internal fogging. Argon gas maintains its protective properties over a wider temperature range. Argon gas does not diffuse as quickly as other elements, extending the service life of the optics longer. This is just one example of optics using argon. There are many others. Argon has a larger molecule then Nitrogen. I am told that it won't leak out as easy as nitrogen. But its expensive and nitrogen is not. It is certainly not anywhere close to being as common as nitrogen but it is used.Just Google argon/ binoculars, optics . I would guess the main reason its not used very often is cost. There may be others but I am not aware of them. Google argon /scopes / purging and you will find tons of examples. I most often see it in the high end optics which leads me to believe cost is why nitrogen is the product of choice.The only advantage that argon has over nitrogen that I can tell is the larger molecule size which would help it stay inside the seals. |
| I was wondering about argon. Its actually pretty cheap, if you get it in bulk. I am a welder, and get large cylinders filled for 55 bucks. Thats ALOT of argon. I build SS headers and other race parts, and what I waste on back purging one tube, would easily do 5 pairs of goggles. Go find a friend that is a welder and has argon (TIG or aluminum MIG) and see if you can steal a dollars worth of argon. |
| I am not sure about chemical reactions between helium and the seals, but the main reason that helium would be a poor choice is because of the small size of the molecules. We helium leak test critical service valves because it is the most stringent method possible. In theory, the farther down the periodic table that you get with an inert gas, the slower the leakage rate. |
| I will give you a clue in, all argon is the same. Same with oxygen. The gas supplier has one tank, one pump, and one fill station. Its all the same. In aviation, there is some discussion about using industiral oxygen or medical oxygen for aviatiors breathing oxygen. Its 100 percent all the same stuff. Ask your local gas supplier if there is a difference, he will verify what I have said. Many people hear "welding" and assume that its crude stuff. remember, that if there was ANY impurity, an super hot arc, and a molten pool of titanium would show it instantly. Its good, believe you me :) |
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Yes, there is only one argon, nitrogen, oxygen, it is how it is handled and stored. The nitrogen tanks at the back of the hospital doesn't get it's fill from the local welding shop. The nitrogen may be all produced at the same facility, however, how it is stored and shipped is different. Here is an excerpt from the ANVIS maintenance manual: 3-9 PURGING Each monocular of the ANVIS is filled with dry nitrogen and sealed to prevent dirt and moisture from degrading the optical performance. In addition, maintaining a slight positive pressure with the nitrogen enables the objective focus and eyepiece focus rings to move smoothly. As required, the ANVIS must be purged with nitrogen every 6 months. Use the following procedure to purge the monocular. NOTE If a monocular will not hold a purge, check for a cracked monocular housing, defective valve, worn preformed packing, or a worn purge adapter using the leak-detection compound. CAUTION There are different types of nitrogen available for AVIM personnel; however using the wrong type will render the ANVIS inoperable. Do not use oil-pumped nitrogen or the ANVIS will be coated with an oil film on the interior optic and component surfaces. Use only water-pumped nitrogen. |
| Helium is almost impossible to contain . It is used for mixed-gas diving . It can leave your body and enter your dive-watch . If it doesn't have a purge valve ( such as the ROLEX Sea-Dweller , the watch can explode as you surface ... I saw a picture of a neoprene wet-suit , worn by a deep-sea diver . It had expanded to the point that it appeared to be for a man around 8 feet tall ... |
| I think the Army TM is also a little out of date when it comes to the type of nitrogen. Dry pumping is pretty much the standard but is not mentioned. I spoke to an Army Technical expert on NVGs a few years ago about this and he said as long as the nitrogen is not oil pumped you are good to go. |
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