Cheap vacuum storage can

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I made a cheap vacuum storage can for 7018 rods. I used a section of  4 inch PVC pipe and two plastic end caps. I pull a vacuum on a small hole in the center that has a piece of tape over it. When I remove the vacuum hose, the tape seals the hole acting like a check valve. To remove the lit I just pull the tape off and the top piece of plastic comes loose. I am not sure if storing rods in a vacuum is equivalent to storing at 250 degrees but it uses no power and my vacuum pump pulls down to 1mm of mercury so there can't be much moisture in the tube.  (99.9% of the air and moisture is removed at 1 mm mercury) I made one using a smaller tube but the vacuum did not provide enough force to crush the O ring and prevent air from entering. http://i118.photobucket.com/albums/o...nut0/tube1.jpghttp://i118.photobucket.com/albums/o...nut0/tube2.jpgLast edited by Taz; 02-04-2009 at 04:16 PM.Reason: pictures missing
Reply:Do you have a chamber large enough to put the whole tube into? Would you call the tape a "flapper valve"?
Reply:I use a hose that has an inside diameter of about a half inch. I place it over the small patch of tape and pull the vacuum. When I lift the hose the tape immediately seals the hole.
Reply:Pictures?A butterfly without wings, is just an ugly bug
Reply:As moisture is the real killer of 7018 a vacuum should work. The trick is to keep is sealed. I know from experience that not all tapes will keep a good seal. I used to O2 clean dive tanks and after rinsing and drying, we would flood the tanks with Nitrogen to prevent moisture and air from rusting the tank interiors and seal with tape until the valves were cleaned and ready to install. Some of the PT wouldn't listen and just used what ever tape they could lay their hands on, often making tape. That was fine for keeping out dirt before we cleaned the tank but would not stop moisture and air from entering. I found Plastic tape like elect. tape would stop moisture but would not stay stuck well enough to seal, Duct tape usually sealed and did stay so I used the plastic tape covered by duct tape to seal the tanks.I'd keep an eye on it and see how long the vacuum lasts, and go from there. The problem will be that when the vacuum fails it will draw air into the tube. (We had this issue because the tanks were hot from drying and when they cooled they formed a partial vacuum and wanted to suck in moist air causing rust.) If you have a humid day, the moisture will enter and get trapped as once the pressures equalize you will loose your air flow. In the short term this should be fine, but don't expect good long term storage with out constant upkeep.Neat idea though!
Reply:I used plumbers putty on the edges where the plastic meets the PVC pipe. There is  tape over the outside edges just to hold it together when vacuum is released.  I have had it holding for a week and based on the curvature of the plastic being deformed from the vacuum, there has not been any leakage.
Reply:If you did have trouble with the vacuum holding for a long time, it would be easy to thread a micro-valve into the end and first draw the vacuum, then refill with Argon. Personally, I think that the continued exposure to the vacuum will continue to draw out (any) moisture for a while whereas Argon will just keep it from rehydrating. With no vacuum, you'd need something to hold the end on too.
Reply:Oldiron, I respectfully disagree with one thing you said here.  I don't think you can dehydrate lo-hi rods just by pulling a vacuum on them.  I think the water reacts chemically with ingredients in the rod flux.  Once this happens, it takes heat to cause those reactions to reverse.  Just pulling a vacuum at room temp isn't going to draw the water back out of the rods.This is why re-baking XX18 rods has to be done at a higher temperature than just storing them.  The higher temps breakdown the chemical bonds holding water in the flux coating.Holding dry rod in vacuum works just fine.  We've got some rod in the shop that's vacuum sealed in mylar bags.  It's dry until it's opened.In fact, it just occurred to me...I wonder if you could use one of those vacuum storage units they sell for packaging food to vacuum seal rods?  Could be an economical way to buy rod in bulk, and then store in smaller amounts....Anybody ever tried this? Originally Posted by Oldiron2If you did have trouble with the vacuum holding for a long time, it would be easy to thread a micro-valve into the end and first draw the vacuum, then refill with Argon. Personally, I think that the continued exposure to the vacuum will continue to draw out (any) moisture for a while whereas Argon will just keep it from rehydrating. With no vacuum, you'd need something to hold the end on too.
Reply:I am not sure I agree with your theory. Heat and a vacuum should both do the same thing, remove the water. Heat does it by evaporating the water and a vacuum does it by reducing the atmosphere inside the container making the water evaporate.The vacuum essentially makes water boil at room temperature by lowering the pressure inside the vessel, removing the moisture. The only thing to do is pump the vessel long enough to remove the moisture from the vessel, then seal.  I knew an old man many years ago that had a steel box he made for a rod oven. He welded the box air tight. The door had a bead of silicone around it. When the door was closed it smashed the silicone between the door and the box making an airtight seal. He put a valve on the box (an air conditioning valve) and attached his vacuum pump to it. He bought rods in bulk and stored them in this box, sometimes for months before opening it and removing some. It seemed to work for him, he had it and used it for many, many years.
Reply:Bob,New rods would be dry(hopefully) when packaged and shipped by the manufacturer.  pulling a vacuum on these would keep them dry indefinitely.My only concern would be with trying to renew or refresh rods that were exposed to moisture by only pulling a vacuum on them.  Some chemical compounds that react with water do not release moisture under vacuum alone.  Some require heat in order to give up moisture.  The difference is whether or not water absorbs into the material or if there's a chemical reaction between some ingredients in the flux and water.  If the former, then you're correct and vacuum will allow the water to 'boil' away.  If the latter, then no amount of vacuum at room temperature may work.It's all somewhat academic; since I don't know exactly what's in the flux on xx18 type lo-hi rods.  I'm just suggesting that it might not work...  Beside, if you're concerned about proper storage, and welding to some code, I've never seen or heard of a WPS that allows for any other treatment than:storage in a rod oven, rebaking according to manufacturer's specs, or only using new rod from a sealed container.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Oldiron, I respectfully disagree with one thing you said here. I don't think you can dehydrate lo-hi rods just by pulling a vacuum on them. I think the water reacts chemically with ingredients in the rod flux. Once this happens, it takes heat to cause those reactions to reverse. Just pulling a vacuum at room temp isn't going to draw the water back out of the rods.This is why re-baking XX18 rods has to be done at a higher temperature than just storing them. The higher temps breakdown the chemical bonds holding water in the flux coating.Holding dry rod in vacuum works just fine. We've got some rod in the shop that's vacuum sealed in mylar bags. It's dry until it's opened.In fact, it just occurred to me...I wonder if you could use one of those vacuum storage units they sell for packaging food to vacuum seal rods? Could be an economical way to buy rod in bulk, and then store in smaller amounts....Anybody ever tried this?
Reply:one time i thought abouttaking a 1ft length of pvc caping one end and drilling a 1/2in hole in it so i ca thread in a 1/4npt 1/4 turn ball valve and put on a quick conect and on the other end have a drain clean out (threaded adapter and threaded plug) have everything glued and threads with teflon tape have a quick conect on the vacume pump keep it conected to pull out any mosture released from water boiling at room temp the then flip the valve and disconect the pump we I need rod just flip the valve to release the vacume unscrew the plug get my rod when done reaply the vacume