If the fitting and regulator are bought separately then some 1/2" wide Teflon tape is recommended for assembly since it is a clean and inexpensive way of sealing pipe joints. Looking into the open end of the nipple wrap the tape clockwise around the threaded end for 1.5 to 2 turns, working from the open end backwards. If you want to do a neat looking job, the tape may be slit lengthways to make it 1/4" wide, but this is not a requirement. A brass nipple may shrink somewhat during tightening and need a bit more tape than a harder metal like stainless steel would. The Teflon tape should only be used on the end of the nipple that attaches to the regulator body, NOT to any part of the cylinder end.
The regulator end has tapered threads and uses them directly for sealing. The cylinder end has straight threads and depends upon the precision mating of machined metal surfaces to seal. The cylinder end threads simply apply the clamping force.
Before attaching the CGA fitting to the cylinder the user should put on safety glasses and good hearing protection. The cylinder valve can then be cracked slightly to blow out any dust or debris. After closing the valve, inspect the cylinder valve and nipple for any abrasions, nicks, gouges, embedded particles, etc., before attachment is made.
You will need two wrenches (not adjustable pliers) to equalize the torque, particularly on the cylinder valve where it should be minimized. Put one wrench on the fitting and the other wrench on the cylinder valve and make the join.
Once the regulator/gauge cluster has been mated to the cylinder, the delivery hose can now fitted to the regulator and the metal wand to the other end of the hose. The wand is nothing more than a short length of metal tubing at least six inches greater in length than the depth of the buckets to be filled. Copper water line works well.
When the joins have been made, a mixture of a short squirt of dish washing detergent and water can be used to check for leaks. Be certain the detergent does not contain ammonia which can be corrosive. Pour some on each fitting working from the cylinder end outward, opening each valve and pressurizing as you go. Once the leak check is finished rinse off and wipe down all surfaces to minimize the chance of accidents in the future.
If the gas is not to be used at that time then the cylinder valve should be closed and all pressure should be drained to zero in the regulator and gauge. This should be done any time that the tank is not in actual use. If you have purchased your own cylinder then it is a good idea to also acquire one of the plastic valve plugs, similar to those seen with propane cylinders, in order to protect the cylinder valve threads and keep dust, debris and insects out of the valve.
WARNING: Care should be taken that the cylinder is used and stored in such a way as to minimize the risk of the tank falling over. With the regulator and gauge attached there is an increased likelihood of damage occurring to the cylinder valve should the tank fall. Catastrophic failure of the cylinder valve will turn the tank into a high-energy, unguided rocket with the capability of doing great damage and/or serious injury.
B.2.4 PUTTING IT INTO USE
Having assembled and tested your gas system, you are now ready to begin the work of packaging your food. You'll need containers, and food grade plastic or Mylar bags that are a bit larger in internal volume than the container. Next is the dry food you intend to package and a pack of matches or a cigarette. You'll also need to wear the safety glasses and hearing protection you wore when you put the gas system together.
Take the containers you are going to use to store your food in, the bags that will line them and the food you are putting up and place them in some warm (not hot) area long enough for them all to equalize to that temperature. This will mean that the air contained inside them will also be at a warm temperature and make it more likely that it will stay on top when the cool gas from the nitrogen cylinder begins to flow in. The warm gas being on top will be the first to purge from the container, taking a good deal of the oxygen with it.
Line the interior of the container with a plastic bag or Mylar bag. Fill the container with the food product shaking to get it as full as possible. Don't forget to put your desiccant package on the bottom if you're going to use one. You don't want any pockets left between the plastic bag and the container. Once you have gotten it full to just short of not being able to fully put on the lid, gather the top of the plastic bag together or heat seal the edges. If you have sealed it, cut a small corner off of the bag just large enough to allow a probe to enter.
At this point you can either simply flush the bag as described below or draw a vacuum on it first and then flush. If using a vacuum the suction probe should be kept at the top of the bag, just inside of the opening. The gas wand should be inserted to the bottom of the container, taking care not to poke any holes in the liner bag. Once both instruments are inserted, draw the vacuum. When it has reached a satisfactory level, shut off the suction, maintain the seal and turn on the gas.
Open the cylinder valve and set the regulator to a very slow gas flow and begin to fill the bag with gas. You want the container to fill slowly so you can minimize turbulence and mixing as much as you can. It'll take a little while to fill each container, a minute or two per bucket. Just as with dry ice, the idea here is for the cool gas to displace the warmer atmosphere from the container. The bag should puff a bit. When I think it's full I'll hold a lit match above the bag in the air that is escaping from it. If it snuffs right out then I let it run for about several minutes longer to flush out more of any remaining oxygen and remove the wand.
For the most efficient oxygen removal, repeat the suction/gas flushing procedure one more time. When satisfied, tie or heat seal the bag off and seal the bucket. Again, you want to have the bucket as full as possible so that there'll be only minimal air space. You should monitor the containers for an hour or two after filling to check for any signs of bulging or other pressure build up as the cool gas inside gradually warms and expands. A slight positive pressure is OK, but serious bulging will need some of the pressure released.
NOTE: Although the procedure for flushing a container with nitrogen is straightforward enough, actually getting a good purge of the container is not. Nitrogen flushing works best when the food particles are fairly large in size so the gas flow around and through the food is free and unrestricted. Foods such as the larger sized grains (corn, wheat, barley, long grain rice, etc.), legumes and non-powdered dehydrated foods are best suited to this technique. Foods with small particle sizes such as flours, meals, and dry milks will flush with mediocre results.
Because of the difficulties in purging sufficient oxygen from a container to lengthen the shelf life of the food it contains many commercial suppliers have dropped this technique in favor of using oxygen absorbers. There is no reason that inert gas flushing and oxygen absorbers cannot be used together and one good reason that they should. If you are using five gallon plastic buckets as your storage containers, it has been observed that absorbers used in unlined pails can cause the air pressure inside the bucket to drop enough for the walls to buckle, possibly leading to a seal breach or a stack collapsing. For this reason, flushing with inert gas (nitrogen or CO2) might be a good idea, in order to purge as much oxygen as possible so that the pressure drop caused by the absorber removing the remaining oxygen will not cause the bucket to buckle. Liner bags can ameliorate the vacuum problems.
A big note of thanks to Lee Knoper for his assistance in putting together the above compressed gas information.
Updated: 9/18/96; 4/16/97; 7/21/97; 10/20/97; 9/15/98; 11/02/99; 12/01/03
Copyright © 1996, 1997, 1998, 1999, 2003. Alan T. Hagan. All rights reserved.
Excluding contributions attributed to specific individuals or organizations all material in this work is copyrighted to Alan T. Hagan with all rights reserved. This work may be copied and distributed for free as long as the entire text, mine and the contributor's names and this copyright notice remain intact, unless my prior express permission has been obtained. This FAQ may not be distributed for financial gain, included in commercial collections or compilations, or included as a part of the content of any web site without prior, express permission from the author.
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