Help with valves for a dewar
Help with valves for a dewar
(OP)
Hi everyone,
I'm going to be working with liquid nitrogen for the first time and have some questions about valves. We would have prefered to work with a non-pressurized dewar, for the sake of simplicity and safety, but meager budgets led us to a used Alloy Products 304 stainless pressurized one.
It appears to be in good condition, but as a matter of principal I don't trust the valves on the thing, especially the relief valve.
Can anyone recommend a good source for these parts? I'd prefer a place where a knowledgeable sales person could talk to me on the phone, patiently, as if I'm a 2 year old.
We would like to get an appropriate pressure relief valve, some kind of fail-safe relief (a blow off valve or equivalent), and a gate valve or something we can use to dispense LN2 into a smaller dewar.
As an unrelated question, something strikes me as odd about this dewar: it's not insulated. Is this normal? What's the idea behind a single-wall stainless LN2 dewar? Its got about 18L capacity and is rated to 140psi. How long might the LN2 actually stick around in something like this? And wouldn't it get encased in ice from condensation?
Thanks in advance for any thoughts,
Paul
I'm going to be working with liquid nitrogen for the first time and have some questions about valves. We would have prefered to work with a non-pressurized dewar, for the sake of simplicity and safety, but meager budgets led us to a used Alloy Products 304 stainless pressurized one.
It appears to be in good condition, but as a matter of principal I don't trust the valves on the thing, especially the relief valve.
Can anyone recommend a good source for these parts? I'd prefer a place where a knowledgeable sales person could talk to me on the phone, patiently, as if I'm a 2 year old.
We would like to get an appropriate pressure relief valve, some kind of fail-safe relief (a blow off valve or equivalent), and a gate valve or something we can use to dispense LN2 into a smaller dewar.
As an unrelated question, something strikes me as odd about this dewar: it's not insulated. Is this normal? What's the idea behind a single-wall stainless LN2 dewar? Its got about 18L capacity and is rated to 140psi. How long might the LN2 actually stick around in something like this? And wouldn't it get encased in ice from condensation?
Thanks in advance for any thoughts,
Paul





RE: Help with valves for a dewar
Just to clear up any misunderstanding, the term "dewar" is used to refer to a vacuum insulated container which is often pressurized. James Dewar invented it back in 1892.
Dewars today can be found with maximum pressures of 0 psig to about 500 psig. http://en.wikipedia.org/wiki/Dewar_flask
So you may want to verify you have a "dewar" and not simply an uninsulated, stainless steel vessel of some sort. Here's a decent web page that goes over the basics and provides a few pictures:
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If your container isn't insulated, I wouldn't use it except for extremely brief periods of time and only outdoors in a well ventilated area, otherwise you'll be asphixiated by the gas boiling off. The nitrogen gas will kill you very quickly.
Regarding valves for these things, the main manufacturer for valves is Rego:
http://www.regoproducts.com/cryoflow/
They also make relief valves. However, I'd recommend also Generant for relief valves.
http://www.generant.com/home.htm
In my opinion, the Generant reliefs are better. Both Rego and Generant have very inexpensive products.
RE: Help with valves for a dewar
If it's helpful, here's a link with pictures and a brief description.
http
The one I have is a larger size, and doesn't have the ports plugged up with bolts, but is otherwise identical.
If this is not actually suitable for LN2 I'll be unhappy.
RE: Help with valves for a dewar
RE: Help with valves for a dewar
RE: Help with valves for a dewar
RE: Help with valves for a dewar
It's supposed to pressurize to 140 psi (close to 10 atmospheres). I'm assuming that won't raise the boiling point enough to make a huge difference ... is this correct?
RE: Help with valves for a dewar
The tank looks like it has vapor and liquid draw off lines.
RE: Help with valves for a dewar
http://www.lpgandnh3.com/contactinformation.htm
RE: Help with valves for a dewar
At this point I'm strongly considering getting rid of the dewar. I'm afraid that being uninsulated, it's not going to be useful (and may eveen be dangerous, as ianuts suggests). I need something that wouldn't lose more than 25% over the course of several days.
It also seems to me this thing would get encased in ice from condensation, and be difficult to handle even if it didn't.
Unless someone thinks I'm wrong about all this, I'm going to look for a new owner for it ... someone who has use for a pressurized, uninsulated LN2 tank.
RE: Help with valves for a dewar
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Plymouth Tube
RE: Help with valves for a dewar
If you're not sure, get a hold of the manufacturer or use Edstainless's suggestion.
As far as valves go, you have to be much more specific. There are many manufacturers who can supply a decent valve for use with LN2, but the size, type and pupose must be known to be of much help.
For relief valves, I've had good luck with Farris and Anderson-Greenwood. However, we did all the sizing and selection in-house and just ordered the parts. For an 18L container with good insulation, most relief valves are going to be bigger than you really need. Look into API codes 520, and 521 for guidance. Some suppliers may be willing to help too.
RE: Help with valves for a dewar
In other words, more like a beer can than a coffee thermos.
RE: Help with valves for a dewar
Heed warning about N2 in a closed space. All our Dewars in the labs and shop are vented to outside.
Take a look at thread725-217421: The Dangers of Argon Gas about Argon gas in a confined space. Though this one is about Argon, Nitrogen will do the number a lot quicker.
Personal addenda:
I've help recover two bodies from tank cars where N2, due to O2 depletion was the killer. I damn near had to fight to prevent two other people from rescuing their coworkers. It was real bad as one of the victims was his brother.
More personal I got a coworker, our group, out of vessel just in time as the N2 was building up very rapidly. He was unaware anything wrong and a little giddy as he was sent to medical. The doctor later told me that he had about 1 minute left on his clock when removed. This was on may way to lunch. Lunch was very enjoyable that day.