by Sara McCaslin Sara McCaslin No Comments

R-410A to R-454B: What Nobody Told You About Your Seals

The HVAC/refrigeration industry in the US is still in the midst of transitioning to A2L refrigerants (R-454B, R-32, etc.) that replace R-410A. These changes are required as part of the Environmental Protection Agency’s AIM Act and its mandate of a stepped phasedown reaching 40% below baseline by 2024 and 85% by 2036. This has forced HVAC manufacturers to shift away from R-410A to lower-GWP alternatives. 

And with that shift has come some surprising seal failures. A piece of HVAC equipment that has worked for 15 years starts experiencing seal leaks, hardening, or swelling for the first time. This is a serious compatibility issue between low-GWP refrigerants and traditional sealing solutions.

This article looks at the causes behind these failures, the failure modes involved, and seal materials to consider in solving these issues.

A Chemistry Lesson

The mechanisms behind the new seal failures occurring with low-GWP A2L refrigerants can be explained with some rather basic chemistry. 

Loss of the R-125 Buffer 

When swapping R-410A (a 50/50 blend of R-32 and R-125) for R-454B (68.9% R-32 / 31.1% R-1234yf) or pure R-32, the solvent properties of the working fluid change significantly. R-125 acted as a flammability suppressant and modified the polar solvency of the mixture. 

Next-generation A2L blends like R-454B remove R-125 entirely, and R-1234yf is itself a smaller, more polar molecule than R-125. The shift, then, is not just R-125’s absence, but also R-1234yf’s more aggressive solvency actively driving elastomer attack. The result of switching to A2Ls has been significantly higher fluid solvency against elastomers than R-410A produced. 

Enhanced Polymer Penetration

Higher concentrations of R-32 and fluorinated alkenes (HFOs) exhibit smaller molecular sizes and higher dipole interactions, increasing their diffusion rates into elastomeric matrices.

Polyolester (POE) & Polyvinyl Ether (PVE) Synergy

In addition, A2L refrigerants in US systems typically rely on Polyolester (POE) oils. The refrigerant lowers the viscosity of the oil and enhances its ability to penetrate elastomer matrix structures. As a result, the seal fails not from the gas alone, but from the combined refrigerant-oil working fluid. 

The Three Primary Failure Modes

There are three failure modes associated with the chemical reactions just discussed: gland overfill, post-maintenance leak, and RGD (Rapid Gas Decompression). 

Excessive Swell / Gland Fill-Ratio Exceedance

Overfilled seal glands, regardless of cause, lead to issues with extrusion into clearances, increased friction on dynamic shafts/spools, nibbling, and permanent mechanical tearing. This may initially appear as a lubrication issue, but it is not. The polymer matrix is absorbing the refrigerant/oil mixture, causing volume expansions exceeding 15–20%. Note that the seal was correctly sized and installed. The volume growth occuring afterward is from chemical absorption, not from an installation or specification error.

The “Post-Maintenance” Leak

As refrigerant permeates the seal, it leaches out the low-molecular-weight plasticizers, processing aids, and cross-linking agents from the elastomer. When this happens under system pressure, the seal appears tight because of swell. However, once the system is evacuated, vented, or cycled off, the absorbed refrigerant off-gasses from the seals. This off-gassing leaves behind an elastomer that has lost volume. The seal then shrinks below its original dimensions, losing compression set and causing sudden leaks.

Rapid Gas Decompression (RGD)

Next is RGD, which is a well-established failure mode in high-pressure gas sealing (e.g., API 6A, NORSOK M-710 test protocols) that A2L refrigerants newly expose HVAC seals to because of their smaller molecular size and higher solubility. In short, A2L molecules are able to permeate high-pressure elastomeric seals. During a rapid system pump-down or sudden pressure drop, the gas trapped inside the elastomer pores expands faster than it can diffuse out. The result of RGD is internal blistering, micro-fissures, and catastrophic seal rupture from the inside out.

Compatibility is at the Core

A2L systems commonly pair with different POE oil formulations than their A1 predecessors. It is, however, key to remember that the oil in A2L refrigerants is just as much a part of the compatibility question as the refrigerant itself. Testing a seal compound against R-454B alone while ignoring the oil is only testing half the problem. 

Seal Material Considerations

The information below summarizes the most commonly used materials for HVAC seals and their performance for both R140A and A2L refrigerants.

Sealing MaterialR-410A CompatibilityA2L (R-454B / R-32) RatingPrimary Risk & Failure MechanismsEngineering Recommendation
NBR (Nitrile)Acceptable Baseline (known long-term POE extraction risk)HIGH RISKHigh extraction of plasticizers; severe shrinkage post-evacuation. Swell varies unpredictably with ACN content.Not Recommended. Replace with peroxide-cured FKM or PTFE.
HNBR (Hydrogenated Nitrile)Good / ExcellentMODERATE TO HIGHHigh swell with low-ACN grades; low-temperature flexibility loss with high-ACN grades.Requires rigorous validation per compound formulation.
FKM (Standard Bisphenol-Cured)Standard ChoiceCONDITIONALVulnerable to chemical attack by basic additives/amines in PVE oils and polar A2L mixtures.Avoid standard grades. Use low-swell peroxide-cured FKMs.
FKM (High-Fluorine / Peroxide-Cured)ExcellentGOODSignificantly reduced swell and chemical resistance against POE/PVE mixtures.Recommended for static O-rings requiring elasticity.
EPDM*Specialty UseSEVERE FAILUREIncompatible with synthetic POE/PVE lubricants, causing immediate degradation and extreme swell.Prohibited in POE/PVE lubricated systems.
PTFE / Virgin & Filled PTFE**Premium / InertEXCELLENT (BEST PRACTICE)Zero chemical absorption, zero swell, zero plasticizer extraction, immune to RGD.Best Practice. Ideal for dynamic rotary shaft seals and control valves.
Fluorosint® 500 PTFE**Premium / InertEXCELLENT (BEST PRACTICE)Synthetic mica-filled PTFE; virtually immune to RGD, chemical swell, and leaching.Superior Choice. Offers lower thermal expansion and greater deformation resistance than standard PTFE under heavy load.
Fluorolon 1065**Premium / InertEXCELLENT (BEST PRACTICE)Modified PTFE compound with high chemical inertness and zero extraction risk.Cost-effective alternative to standard virgin/filled PTFE for aggressive A2L and lubricant environments.
Polyketone (PK)**GoodEXCELLENTRigid semi-crystalline thermoplastic; non-porous structure eliminates RGD and plasticizer leaching.Eco-friendly engineering option. High wear and impact strength; best suited for anti-extrusion back-up rings or structural seal components.
PVDF (Kynar®)**GoodEXCELLENTHigh mechanical strength and creep resistance; resistant to chemically aggressive refrigerants.Recyclable engineering polymer. Ideal for rigid back-up rings, valve seats, and high-pressure containment components.

*Note on EPDM: This incompatibility predates the A2L transition and applies to ester-based lubricants generally, not to the A2L refrigerant molecule itself. 

**Thermoplastic options (PTFE, Fluorosint, Fluorolon, Polyketone, PVDF) are not elastomers and are not drop-in replacements in standard elastomeric O-ring grooves. They typically require redesign (e.g., spring-energized lip seals) or are used as backup/anti-extrusion rings.

Conclusion

As legacy systems are retrofitted for use with A2L refrigerants, it is important to consider the compatibility of both the refrigerant and its oils with the seal materials. If you are looking for an effective seal design that is resistant to the harmful effects of A2L refrigerants, talk to the seal experts at Advanced EMC. Our team is familiar with HVAC / Refrigeration seal needs and is ready to work with you from design to installation and beyond.

PTFE Rotary Shaft Seals
by Daniel Mays Daniel Mays No Comments

Pressure Cycling and Pulsation Issues in Polymer Seals

Pressure cycling and pulsation can lead to seal issues like extrusion, blow-by, and fatigue damage. There are, however, some design principles that can address these issues and mitigate their effects. This article takes a look at the issues related to cycling and pulsation and addresses six key design considerations related to them.

Pressure Cycling and Pulsation

Pressure cycling refers to repeated transitions between low and high pressure, including dwell time at each level. Pulsation, on the other hand, is associated with high-frequency pressure oscillations superimposed on the mean system pressure (often pump- or compressor-driven). Pressure spikes are short-duration transients that exceed nominal operating pressure.

Designing polymer seals for cyclic pressure and pulsation is actually a system-level problem. Consideration must go into the material, energization method, gland geometry, hardware stiffness, surface finish, and validation testing.

Seal Issues Related to Pressure Cycling and Pulsation

When polymer seals are subject to pressure cycling and pulsation, the primary design objective becomes the ability to maintain adequate contact stress and sealing integrity throughout the entire pressure waveform while avoiding extrusion, blow-by, and fatigue damage.

Extrusion occurs when the seal is forced into a clearance gap by pressure, like a soft solid getting pushed into a narrow crack. Blow-by takes place when a pressurized fluid or gas leaks past the seal because there is not enough contact stress. Fatigue damage is the progressive cracking or material breakdown that is caused by repeated loading cycles. Note that each individual cycle can be below the material’s one-time strength limit and still result in fatigue damage.

Signs of Pressure Cycling and Pulsation Issues

There are several signs that pressure cycling and pulsation are causing problems. One of the first is early leakage after a very short run-in period. The seal might also experience intermittent leakage that is related to the duty cycle or pump frequency. Another sign of seal problems is the extrusion of the gear lip, torn edges, or nibbling. Finally, backup ring displacement or seal rotation can also be a signal of issues. 

These problems usually show up in hydraulic actuators, pumps, and manifolds, gas compression stage and valve plates, chemical processing skids with pulsation dampeners, and high-cycle test equipment and aerospace pneumatic systems.

Design Tips for Addressing Pressure Issues

Here are some design tips for working with seals undergoing pressure cycling.

Pressure Waveform

In order to mitigate issues with pressure cycling and pulsation, it is important to look at the pressure waveform and not just the peak pressure. For example, document mean pressure, peak pressure, minimum pressure, ramp rate, frequency, and dwell times. Then identify the transient spikes separately from the steady cycles. Once this information has been gathered, map the waveform to the duty cycle and the total number of cycles.

Polymer

Remember to select the polymer family for the seal based on cyclic strength and creep resistance. Filled PTFE offers good creep resistance and extrusion margin. PEEK and PPS options can lead to a higher modulus, better load retention, and improved wear. UHMW-PE offers low friction but lower stiffness. However, keep in mind that the material choice should also be considered with regard to the temperature, media, PV, and allowable deformation.

Spring-Energized Seals

Another excellent option is to utilize spring-energized seals to maintain contact stress when system pressure drops. These seals have pressure-energized lips designed to avoid issues during pressure reversals. In addition, consider the use of dual-acting geometries for bidirectional pressure. And avoid relying solely on squeeze for long-life high-cycle conditions when relaxation is expected.

Seal Gland

When designing the gland, it is important to ensure that the seal is both well-supported and deforms in a controlled manner when subjected to pressure cycling. The compressive fa orce should provide reliable initial sealing force without being so high that excessive creep results over time. Utilize radii and lead-in chamfers to eliminate sharp edges that can result in problematic notches or tears. And when clearances cannot be held tightly, use anti-extrusion features to ensure the pressure cannot force the polymer into a gap.

Backup Ring

Another potential aspect of the design is the use of a backup ring. Its material should be fully compatible with the primary seal and can maintain strength and dimensional stability across the operating temperature range. When deciding between split or solid design backup rings, keep in mind potential issues with rotation and migration during pressure pulsation. 

Surface Finish

Under pressure cycling, the surface and interface details matter significantly. Small leak paths are the potential problems here, and can be addressed. First, the counterface roughness should result in a surface that supports film formation but does not lead to bypass channels or issues with abrasive wear. The lay direction should prevent machining grooves from behaving as micropumps during pressure fluctuations. In addition, if there is a possibility that erosion, wear, or corrosion could affect the roughness over time, use coatings or surface treatment that will stabilize the counterface.

Conclusion

Pressure cycling and pulsation can cause extrusion, blow-by, and fatigue damage. Careful design, however, can mitigate these issues.

If you are working on a seal design that must provide reliable performance when subject to pressure cycling and pulsation, let the polymer seal experts at Advanced EMC help. Contact us today.