[Gutterz]

I wonder if the pressure is making it leak faster? When I was down at Kingpins the other day he doesnt put tops on his their just open. I asked him about evap an he said it dont evap that much an told me to look in the one that it should still be full from the day before an it was. So im realy not sure whats up.

[Chuchnit]

Originally Posted by Gutterz

I wonder if the pressure is making it leak faster? When I was down at Kingpins the other day he doesnt put tops on his their just open. I asked him about evap an he said it dont evap that much an told me to look in the one that it should still be full from the day before an it was. So im realy not sure whats up.

So we just go and hang out with Vince now huh?

Anyways I was wondering about that because I mean I can just fill the sucker and bench it the same day. I just don't wanna lose half my ln2 in no time flat.

[HITandRUN]

Originally Posted by Gutterz

I wonder if the pressure is making it leak faster? When I was down at Kingpins the other day he doesnt put tops on his their just open. I asked him about evap an he said it dont evap that much an told me to look in the one that it should still be full from the day before an it was. So im realy not sure whats up.

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.

Originally Posted by Chuchnit

Seriously I just don't understand how no top will evap less than with something covering the neck.

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

[Chuchnit]

Originally Posted by HITandRUN

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 less 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.

[2chesapeakes]

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.

[Buckeye]

Originally Posted by 2chesapeakes

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.

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

[HITandRUN]

Originally Posted by Chuchnit

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.

No clue mate since I never had a leaking one. I mean you could test it yourself by purging it with pressured air. Make up rig that fits the top with a gauge and a ball valve and than pressurize this thing.