That's pretty cool man. Yah, I knew you lived close. Hmm, this makes me want to risk it and just fill the sucker without a lid. Seriously I just don't understand how no top will evap less than with something covering the neck. Buckeye...... got any info on this? You are the resident dewar, SSD, and who the hell knows what else genius around here.

can u remove the spout an put a cork on it? Some of the ones Ive seen on Ebay just have a cork with threaded rod to hold it secure from the sides.

My dewar didn't come with a plug so I use something like this: Link

Thats pretty sweet.

also chuch if u need somthing now, you can check the auto parts they have replacement rubber freeze plugs for motors. Their similar to what Ocgmj posted but they tighten down with a nut. They worked well when I had to leak test banshee motors after rebuild.

http://images.outdoorpros.com/images...9849-61834.jpg

You can pick them up at pool supply ships too, although they will probably charge more for them.

Glad you guys were mentioning this though as I was wondering myself what to get to top a dewar :)

Yeah I had one of those as well! It was a 20L dewar. You could fill it up to the top and leave it there for a week without barley loosing 1/4 of it. I dont see how the relief valve would do it. I think its more bad vacuum in this case.

Pressurizing the dewar with a bad vacuum will make it leak out faster so leaving it not pressurized will last longer.

Interesting info there HitandRun. So if it is a bad vacuum, how fast would you guess my evap rate is going to be on the dewar? I literally live right by the gas company so I could start benching pretty fast.

What the guys at Air gas told me was to fill the dewar all the way. If the outside of the dewar frosts up or condensation forms on the outside of the deward chances are the vacum is no good. If no rost or condensation is present. When I was researching my dewar the manufacturer had listed a normal evaporation rate. If i remember correctly the way to test mine is to fill it weigh it leave the vent open and weigh it 24hrs later. The has listed the normal evaporation rate in the manual. My dewar is what is consider a low pressure dewar. It is designed to maintain 22psi so once filled it only takes a few minutes to build enough pressure to pour. The one I had borrowed was a storage dewar it is not designed to build pressure. It took 1.5 days for enough pressure to build to be able to usethe withdrawal device on the dewar. If I wanted to use it right away I would have to pour from the dewar to the thermos.

i have the same dewar i think it's just where you keep it it may be different cuz i got my lab 30 a about 3~4 month ago maybe longer and i only fuled it once and weather is very cold in tennessee back then for me at least and there was ln2 left over till like 2 weeks ago i used most of it when i got it and had about 5L left in it....
make sure the cap on the dewar is good and it's in a place that's cold
and my mother in her work they had to fule it every week may be that's because the amount of usage idk i am baned @ work so... yeah,,, GL BRO

That sounds like how mine is, it never vents either but it only takes over night to build up pressure.

I had a 160L rental that was that way, took for ever to let pressure rebuild. But I was filling my 50L from it so I was really dumping pressure.

I am not sure why LN2 doesnt evap right away with open Dewars. I think it because its inside the Dewar which has been chilled down so it keeps the mass of LN2 cold for long periods of time.

I know most don't worry about it as most likely they get one filled and then use it all up over a weekend. I don't think it would last a long time tho., what bencher in there right mind would let a Dewar with LN2 sit and not use it for something, like Ice Drinks, Cooking With LN2, freezing bugs, cats tails etc :)