# Leak testing with nitrogen

• 11-03-2012, 02:17 PM
burto
Leak testing with nitrogen
I always thought nitrogen stayed the same pressure in a system even if ambient temps change from one day to another.Do you guys see this to be true?
• 11-03-2012, 02:26 PM
RoBoTeq
Nitrogen is subject to pressure changes at varying temperatures, just not as much as refrigerants and other gases are.
• 11-03-2012, 04:54 PM
burto
Got it,If I put in 300psi and return in a day or two and temps are ten degrees of each other,what do you think 5psi give or take?
• 11-03-2012, 05:30 PM
barbar
• 11-03-2012, 08:23 PM
jpsmith1cm

Here's a good thread on the topic.

If I remember right, there's also a calculator that will allow you to compute what your target pressure should be, given known conditions.
• 11-03-2012, 09:21 PM
Tech Rob
Quote:

Originally Posted by burto
Got it,If I put in 300psi and return in a day or two and temps are ten degrees of each other,what do you think 5psi give or take?

I think at this point, you know as much about the system as you would if you had done nothing at all. Do a real leak test, or at the very least pull a vacuum and see if it holds. Don't be lazy.

:.02:
• 11-03-2012, 10:01 PM
2sac
300psi? A little overkill maybe?
• 11-03-2012, 11:19 PM
TriplePoint
Here is a snippet about ideal gas law that will answer you question.

Attachment 324241
• 11-03-2012, 11:41 PM
Chuck
I recently used this formula for a system that required me to document a standing 24 hour pressure test at 600 psi. I pumped it up and ended up with 604 psig on my digital Testo. Also took temp reading. Wasn't able to come back next day, ended up being 5 days and pressure was at 608 psig. I don't remember the temp change, it wasn't much, but using the forumla, it showed that 608 was right where I needed to be.

Jim Bergman wrote an excellent article for RSES on how to calculate the pressure change for standing pressure tests. It is in the RSES Journal Archives.