The Real Cold Test

As mentioned in this blogs header area, Cold Test is usually a step in our procedures for repairing liquid cylinders.  Well, I felt it would be a complete injustice if I did not, at some point, explain the blogs namesake, and I figured now was as good a time as any to do it. 

Okay, first, lets talk about liquid cylinders themselves.  What are they, you ask?  Well a liquid cylinder, just like a high pressure cylinder is a tool used to move molecules, such as nitrogen, oxygen, argon and carbon dioxide.  A high pressure cylinder is very simple and can hold molecules almost indefinitely.  Liquid cylinders are much more complicated vacuum insulated vessel that can hold more than ten times the amount of molecules a high pressure cylinder can contain.  So, basically, liquid cylinders are giant, complicated, expensive thermoses that are used pretty much anywhere for pretty much anything.  Pretty neat family business, huh?

Well, the key to these cylinders and their epic abilities is all in their vacuums.  If your vacuum goes bad, there goes your product, along with your profits.  The vacuum of a liquid cylinder is made in it's annular space,
which is the insulated space between the smaller inside tank and the outer tank that you can see.  Because all vacuums are imperfect, every liquid cylinder will naturally lose product over time.  This is referred to as the "Normal Evaporation Rate" or N.E.R. in the biz.

To check the tank's vacuum and make sure the N.E.R. is in an acceptable range (less than 3% per day), West Cryogenics performs a few Cold Tests.  This is standard work we do on every vacuum repaired tank that comes through our door.  One common Cold Test is what we refer to as a Liquid Full Pressure Test.
Here's a simple version of how it goes:
  1. Pressure up the tank and check for leaks.
  2. Remove pressure and fill tank with NF liquid nitrogen.
  3. Allow the tank to cool down for one hour with the vent open.
    • If the tank is still venting heavily after cool down, is abnormally cold or has condensation on the outer jacket, this means that the vacuum is insufficient to maintain product.
  4. Close vent and make sure all valves are closed.
  5. Leave tank undisturbed for 16 hours (this may be a good time for that C.S.I. marathon you've been dying to have).
  6. After 16 hours, the pressure gauge should not read more than 50 psi.
If your tank has built to more than 50 psi, the vacuum is marginal at best (sorry charlie).

But don't worry, we will fix it!  Okay, so I don't think you will be doing any of these any time soon but isn't it so gosh darn interesting!?  The Liquid Full Pressure test is just one of the many tests we perform every day to make sure our customers' cylinders are safe and saving them money.  We would hate to see any tanks wandering around with bad vacuums, so remember that vacuum is our middle name.  That's right, we are West "Vacuum" Cryogenics, but it's just West Cryogenics to our friends.

Think your tank might have a vacuum problem?  Comment below, email, or just call us and we'll answer any questions you can think of!

1 comment:

  1. Well Morgan,

    This was a very interesting post. I was just put on to you guys today and was poking around your site and discovered your blog. Some good ifno. I am looking for info like this since we are relativly new to the liquid business. You may have a previouse post on the info I seek. We have a few customers that are complaning about a few liquid cans we have. Some of them even being recently referbed by someone other than West Cryogenics. Do you by chance have some type of checks we can do before sending them to you so we can tell the diferance between a customer trying to pull a fast one and a tank with a true problem. Any info would be greatly appreciated.