# Thread: Leak testing with nitrogen

1. ## 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?

2. Nitrogen is subject to pressure changes at varying temperatures, just not as much as refrigerants and other gases are.

3. 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?

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http://hvac-talk.com/vbb/showthread.php?t=846662

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.

5. 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.

6. 300psi? A little overkill maybe?

7. Here is a snippet about ideal gas law that will answer you question.

8. 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.

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