Leak testing is a critical part of maintaining low-pressure centrifugal chillers. But when leak testing a low-pressure centrifugal with nitrogen, what is the maximum test pressure you should use?
So, what’s the safe limit?
When leak testing a low-pressure centrifugal with nitrogen, the maximum test pressure should never exceed 10 psig. Why? Because low-pressure systems operate differently and contain sensitive components that can rupture under high pressure.
In this article, we’ll explain:
- Why 10 psig is the industry standard
- What happens if you go over that limit
- Safer ways to leak test low-pressure chillers
- Manufacturer and EPA guidance
Whether you’re an HVAC pro or a facility manager, this guide will help you stay compliant, safe, and efficient.
Why Leak Testing Matters for Low-Pressure Centrifugal Systems
Low-pressure chillers—typically using refrigerants like R-11 or R-123—operate under vacuum or slightly above atmospheric pressure. These systems are sensitive and efficient but prone to refrigerant leaks over time.
Leak testing ensures:
- Energy efficiency
- Environmental compliance
- System longevity
For a deeper look into efficient testing, check out How Charged Low-Pressure Refrigeration Machines May Be Most Efficiently Leak Checked.
Because of their design, applying too much pressure during testing can cause more harm than good.
What Is the Maximum Test Pressure With Nitrogen?
According to EPA Section 608 guidelines, when leak testing a low-pressure centrifugal system, the maximum nitrogen pressure should not exceed 10 psig.
Here’s why:
- Most rupture discs in low-pressure systems are set to release pressure at 15 psig
- Testing above 10 psig leaves no margin for error
- Going higher can trigger the rupture disc, releasing refrigerant or nitrogen and violating EPA standards
Learn more about Section 608 standards
So remember:
- Use dry nitrogen only
- Keep pressure at or below 10 psig
Why 10 psig? (Explained Simply)
Low-pressure chillers are not built for high internal pressure. Their components—like rupture discs, gaskets, and seals—are designed for a very narrow operating range.
If you go over 10 psig:
- You risk activating the rupture disc
- You may cause refrigerant loss
- You could face EPA fines for releasing refrigerant
Most rupture discs in chillers are rated to open at 15 psig, so staying under 10 psig is a safe and legal buffer zone.
Want to reduce unnecessary refrigerant loss? Check out What Should Be Done to Reduce Refrigerant Loss From a Purge Unit on a R-123 Chiller?
Safety Tips for Nitrogen Leak Testing
Even though nitrogen is inert (non-flammable), it can still be dangerous when compressed. Here are important safety guidelines:
Do:
- Use a pressure regulator when charging with nitrogen
- Leak test only isolated sections, not the entire system
- Wear PPE (gloves, goggles, and hearing protection)
- Label testing zones with safety signs
Don’t:
- Use oxygen or compressed air (fire hazard!)
- Over-pressurize the system
- Test without confirming the rupture disc rating
Always follow ASHRAE refrigerant safety standards to stay compliant and safe on site.
Alternative Methods to Pressurize for Leak Detection
The EPA recommends that the best way to build pressure in a low-pressure system is by:
- Using hot water to raise temperature and pressure
- Activating built-in electric heaters (if available)
These methods are safer because they mimic the system’s normal pressure rise during operation without introducing external gases.
Nitrogen testing should only be used if heat-based options are unavailable. Learn more in How Charged Low-Pressure Refrigeration Machines May Be Most Efficiently Leak Checked.
Manufacturer Guidance and Component Ratings
Not all low-pressure systems are built the same. That’s why manufacturer specifications should always guide your testing.
Why it matters:
- Different components (evaporators, condensers) may have unique pressure tolerances
- Some systems may even have multiple rupture discs with different pressure ratings
Before you test:
- Check the system manual
- Identify the lowest rated component
- Base your pressure test on that component’s max limit
Want to calculate leak rates accurately? Don’t miss What Is the Best Method to Determine a Chiller’s Normal Charge for Leak Rate Calculations?
Best Practices for Leak Testing Low-Pressure Chillers
Do:
- Keep pressure at or below 10 psig
- Use dry nitrogen only—never air
- Add trace gas (like R-123) to help find leaks with electronic detectors
- Follow EPA and manufacturer guidance
Don’t:
- Use high-pressure nitrogen tanks without a regulator
- Skip checking rupture disc rating
- Assume “more pressure = better results”
Leak testing is about precision, not power.
FAQ
Can I test a low-pressure chiller above 10 psig?
No. Testing above 10 psig may activate rupture discs and cause refrigerant loss. It’s unsafe and not recommended by the EPA.
Why is nitrogen used instead of air?
Nitrogen is dry and inert. Air contains moisture and oxygen, which can damage internal components and react with refrigerants.
What happens if the rupture disc activates during testing?
The system will vent gas, possibly releasing refrigerant and violating environmental regulations.
Final Thoughts
When leak testing a low-pressure centrifugal system with nitrogen, stay below 10 psig—always. It’s not just about avoiding damage—it’s about keeping your system compliant and efficient.
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