Deep Technical Chapters · Pressure Testing & Leak Diagnosis
Nitrogen Temperature Effect
Nitrogen is inert, but its pressure changes with temperature. A lower gauge reading does not automatically prove the system has leaked.
This is the single most common source of false leaks. Nitrogen doesn't leak just because the gauge moved. If you don't account for temperature, you will chase leaks that don't exist — and you will cut into sound systems.
The pressure–temperature relationship
A fixed volume of nitrogen at a higher temperature has a higher pressure; at a lower temperature it has a lower pressure. A system pressurised on a hot afternoon and left overnight will show a noticeably lower pressure in the morning — with no leak at all.
The correct procedure
- Record the test pressure.
- Record the relevant temperature (ambient, pipe surface).
- Allow appropriate stabilisation.
- Understand the pressure–temperature relationship for the test gas.
- Compare pressure changes against the temperature change.
- Investigate the test equipment and test boundary.
- Determine whether the change can be explained by temperature.
- Only then pursue actual system leakage.
Do not invent a universal allowable drop
There is no universal "allowable pressure drop" that applies to every system. The acceptable change depends on the volume, the temperature change, and the test setup. Judge each test on its own conditions.
Field Rules
- 01
"Nitrogen doesn't leak just because the gauge moved. Check the temperature."
- 02
"A pressure test is only meaningful when you understand what can change the pressure."
- 03
"There is no universal allowable pressure drop."
Diagnosis at a glance
What can mislead you
- •A lower overnight pressure interpreted as a leak.
- •A rising pressure on a warming day interpreted as "the system is fine".
How to prove the fault
- •Pressure change matches the temperature change → not a leak. Pressure change exceeds what temperature explains → investigate.
