Dewar update

JTknives

JTknives

Joined
Jun 11, 2006
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Thought I would give an update on my current performance of my cryo dewar. According to my math I have had LN in it for just about 5 months. There is still some in the bottom as we speak but I'm considering filling it maybe next week. 5 months is 150 days and I have been using it a lot more then I thought I would. I have done quite a few of my own knives plus a BUNCH of customers blades. So I am more then happy with its performance and glad I spent the money to get a good one.
 
That's pretty good hold time considering loss every time you use it. They are not a cheap piece of equipment to just sit around and holding liquid gas.

I purchased mine used from a GSA Auction about 6 years ago not cheap back then either. It's a Taylor Wharton 30L that was lightly used in a Lab I would guess, and I was fortunate to find one with the WIDE neck. Price at auction with shipping was just under $500 (new would have been easily double that) I was a little worried at that price it could have a bad vacuum jacket and be worthless. Looks like you're getting your moneys worth out of it!!!
 
Ok I just checked it and I have 2" in the bottom left.
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Here is where you can buy it from the manufacture new, just under $1,900.
https://us.vwr.com/store/product/4617613/vwr-cryopro-canister-storage-tanks-cc-series
 
So long as the vacuum jacket between the inner container and outer shell is not compromised there should be no need for any other thermal protection. The outer shell on my unit stays at ambient with not hint of condensation on hotter days. The real key is to have a GOOD throat plug that will allow the smallest release of gas over a long period of time and if that plug is shot so long gas!
 
I have a 36L I paid $10 for. I'm pretty happy with that, it keeps liquid for about 4 months.
 
I own a MVC 20 liter that I bought used from a manufacturer of climbing hooks. I bought it for a restaurant I was working at, I've used LN at a restaurant in Chicago I worked at. AirGas charged $2 a liter and a $40 delivery fee. Since I started making knives a few years ago it might get some use again when I start doing my own heat treat.
 
got a 20l big mouth and i get about 45 days out of it but for me its a much have i have a frien i the weldig ind. so i get a deal on the fills but when he is not there 5 bucks a L gets salty
good news is i still get 50 or more blades out of each tank full and donate the rest to local school science class
 
I was thinking about a wide mouth but mine is 2.1875" so fits everything I do right now and has really good retention. I find I loose less LN per cryo treatment as the level gets lower. I actually like it where it's at right now becaus I don't have to submerge the blades in the liquid. Just hang them in the dewar with a wire just above the liquid and put the foam cork back in. I did a bunch of research and the testing showed that from the bottom of the foam to the liquid surface is an even -300°
 
JTknives said:
I was thinking about a wide mouth but mine is 2.1875" so fits everything I do right now and has really good retention. I find I loose less LN per cryo treatment as the level gets lower. I actually like it where it's at right now becaus I don't have to submerge the blades in the liquid. Just hang them in the dewar with a wire just above the liquid and put the foam cork back in. I did a bunch of research and the testing showed that from the bottom of the foam to the liquid surface is an even -300°
Click to expand...

Now that's something I've never even considered. I just always assumed you had to be submerged. Good to know!
 
You get a lot less boil off suspending in the cold gas. So much so that I have thought it might be worth looking into getting a second dewar and using one as bulk storage and the other only keep a few inches in it. You would need to keep the second one cold all the time becaus once it warms up it takes a bunch of LN to cool it down again. Sure would be sweet if thy made dewars that where skinny and tall.
 
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JTknives said:
You get a lot less boil off suspending in the cold gas. So much so that I have thought it might be worth looking into getting a second dewar and using one as bulk storage and the other only keep a few inches in it. You would need to keep the second one cold all the time becaus once it warms up it takes a bunch of LN to cool it down again. Sure would be sweet if thy made dewars that where skinny and tall.
Click to expand...

As long as you can keep it cold with enough LN2 before the next refill then why not just buy half as much...it may not last 5 months but you are getting the desired Chill effect -300 +/- without paying for the boil off when full...just a thought
 
JTknives said:
You get a lot less boil off suspending in the cold gas. So much so that I have thought it might be worth looking into getting a second dewar and using one as bulk storage and the other only keep a few inches in it. You would need to keep the second one cold all the time becaus once it warms up it takes a bunch of LN to cool it down again. Sure would be sweet if thy made dewars that where skinny and tall.
Click to expand...

I wonder if you could set up a full "primary" dewar with a little drip pump, or something like a proportional flow pump to slowly drip into a secondary dewar that's set at a lower fill level. You'd probably want to insulate the transfer lines, and I'm not sure what kind of pump would be needed for LN, but I'm just thinking out loud.

If you could keep the loss between the transfer equipment at a minimum, I imagine you wouldn't have to set the flow rate very high at all to maintain a few inches of depth in the secondary. Heck, probably just a gravity fed line from the full to the "empty" with a manual valve that you opened once a week for a second or two would perhaps be enough to get a little more out of your LN. That, or you could set up a solenoid valve that opens for a split second every once in a great while. Again, it'd have to be rated for something like LN. Not sure if that's a possibility, or worth the hassle or not.
 
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