Gasket selection for
refrigeration and cooling systems —
what the application demands
Documentation scope: Approval, compliance and certification references apply to the documented material grade, supplier certificate or listing, and stated test conditions unless a product-specific certificate says otherwise. A cut gasket size is not automatically certified as a separate product just because it is made from a documented material. For regulated applications, confirm the current certificate or listing scope, exact grade, medium, temperature, pressure and market requirement before specifying.
Scope note: This article is an application-selection reference. Final gasket choice depends on the exact medium, oil or glycol chemistry, concentration, pressure, temperature, flange condition and any site or regulatory requirement.
What refrigeration and cooling systems ask of a flat gasket
This article focuses on flanged flat gasket joints on the refrigerant side of HVAC and cooling equipment — compressors, refrigerant pipework, heat exchangers and valves. It does not cover every gasketed joint in general HVAC plant or water-side connections.
A flat gasket in a heating or water system often faces a more stable set of conditions — steady temperature, consistent pressure, a single medium. A gasket in a refrigeration or cooling system faces a more variable environment. Understanding what that environment actually demands is the starting point for material selection.
Material properties that matter most in this application
| Property | Why it matters in HVAC / cooling | Standard |
|---|---|---|
| Compressibility | Determines how well the gasket conforms to the flange face under available bolt load. Higher compressibility suits lower bolt loads and face irregularities at compressor flanges. | ASTM F36J |
| Recovery | How much the gasket springs back after compression. Relevant in thermal cycling — the gasket must maintain contact as the flange contracts on cooldown. | ASTM F36J |
| Creep relaxation | How much bolt load the gasket retains over time under sustained compression. Low creep relaxation helps the joint retain bolt load over time. | DIN 28090-2 |
| Specific leak rate | Refrigerant containment requirements are strict for environmental, safety and regulatory reasons. Low leak rate material is particularly important across the refrigerant circuit. | DIN 3535-6 |
| Chemical resistance | Compatibility with the actual refrigerant in service — not generic "refrigerant" compatibility. Must be confirmed per compound from the material supplier's data. | Supplier chemical resistance data |
| Temperature range | Peak and continuous operating temperature should cover compressor discharge temperature on the high-side and sub-zero conditions on the low-side of some systems. | Manufacturer TDS |
Where different gasket grades are relevant
Not every location in an HVAC or cooling system has the same requirements. The appropriate gasket grade typically varies by location:
- Compressor flanges — assess a higher-compressibility grade where vibration, face condition or bolt load makes seating difficult. Vibration, variable bolt load and flange face condition make a higher-compressibility synthetic fibre grade worth considering over stiffer grades where lower bolt loads or face irregularities are a factor. The material must also be confirmed for refrigerant compatibility. FLEXSEAL PRO 350 is one example of a higher-compressibility grade used in refrigerant and compressor applications where compatibility has been confirmed against supplier data.
- High-pressure pipework flanges — rated pressure grade. Discharge pipework operates at the highest system pressures. Gasket thickness should be minimised where possible — thinner gaskets perform better at high pressure. Grade selection should reflect the refrigerant and the flange standard.
- Heat exchanger flanges — media on both sides. Condenser and evaporator flanges may have refrigerant on one side and water, glycol or air on the other. The gasket grade must be appropriate for both media at the operating conditions of each side.
- Low-pressure suction and evaporator connections — temperature range. Low-side connections may see sub-zero temperatures in some systems. Confirm the gasket material is rated for the actual minimum operating temperature, not just the high-side conditions.
- Valve body gaskets — application-specific. Valve body flanges in refrigerant service require the same refrigerant compatibility confirmation as pipework flanges. The operating conditions at each valve location — pressure, temperature, medium and oil carryover — determine the grade to assess.
Refrigerant type and material selection
The refrigerant compound in service is the single most important variable in gasket selection for cooling systems — more so than temperature or pressure alone, which are typically within the range of several viable grades.
Common refrigerant categories and their material implications:
- HFC refrigerants (R410A, R32, R134a): widely used in commercial cooling. NBR binder grades are commonly considered for HFC service, but specific compound compatibility should be confirmed from supplier chemical resistance data — not assumed from the generic HFC category.
- HFO refrigerants (R1234yf, R1234ze): lower-GWP compounds with chemical behaviour that differs from HFCs. Supplier chemical resistance data for the specific HFO compound should be obtained and confirmed before specifying a gasket grade.
- Ammonia (R717): used in industrial refrigeration. Ammonia is chemically aggressive and attacks many rubber compounds including NBR. Material selection for ammonia service requires specific chemical resistance data — general refrigerant listing does not cover ammonia.
- Carbon dioxide (R744): used in transcritical CO₂ systems, increasingly in commercial refrigeration. Transcritical CO2 systems can operate at very high pressure, so selection must use the OEM joint rating plus combined pressure-temperature, leakage, cyclic-load and compatibility data. A headline sheet-pressure maximum alone is not sufficient.
Generic "refrigerant compatible" listings are not sufficient for specification. A gasket material listed as suitable for refrigerants should be cross-checked against the chemical resistance data for the specific refrigerant compound in service — particularly for ammonia, CO₂ and HFO compounds where compatibility is more specific than for HFCs. Request the chemical resistance chart from your gasket supplier for the refrigerant in service.
Installation factors that affect sealing performance
Material selection is only part of the sealing equation in HVAC and cooling systems. Several installation factors consistently affect how well a correctly specified gasket performs:
- Flange face condition: compressor flanges that have been used and resealed multiple times may have scored or uneven faces. A higher-compressibility grade can accommodate more face irregularity than a stiffer material, but severely damaged faces require resurfacing before any gasket grade will seal reliably.
- Bolt torque sequence: uneven bolt tightening creates uneven compression across the gasket face, which can produce leak paths even with a correctly specified material. Cross-pattern torquing to the correct value for the flange and gasket grade is standard practice.
- Gasket thickness: thinner gaskets generally perform better at higher pressures and show less creep relaxation over time. In high-pressure refrigerant applications, the thinnest grade that can adequately compensate for face irregularity is typically the correct choice.
- Old gasket removal: residual gasket material from a previous installation can prevent the new gasket from seating evenly. The face should be clean before fitting a replacement — how to remove an old gasket.
In summary: Refrigeration and cooling gasket selection starts with the refrigerant compound and works outward — compressibility for the flange type and bolt load, pressure rating for the system location, temperature range for both high-side and low-side, and chemical resistance confirmation for the specific refrigerant. No single grade suits every location in a refrigeration or cooling system, and no generic refrigerant listing replaces compound-specific compatibility data.
HVAC and cooling applications are not a single sealing problem.
The right material for a compressor flange is often different from the right material for a high-pressure discharge line, a heat exchanger connection or a suction-side valve. Start with the refrigerant compound, confirm chemical compatibility from the supplier's data, then match compressibility and pressure rating to the specific joint location and flange design.
Practical FAQ
What type of gasket is used in HVAC and refrigeration systems?
Refrigeration and cooling systems use several gasket types depending on the joint design and location: flat sheet gaskets for flanged connections on pipework, compressors and heat exchangers; O-rings for shaft seals and cartridge connections; and spiral wound or ring-type joints in high-pressure sections of some industrial refrigeration systems. For flanged connections in typical commercial and industrial HVAC and cooling systems, compressed fibre sheet gaskets with NBR binder are commonly used where the medium, pressure and temperature are within the material's rated range. The specific grade depends on the refrigerant, operating pressure and whether the joint is on the high-side or low-side of the system.
Why does thermal cycling matter for gasket selection in HVAC systems?
HVAC and cooling systems cycle between ambient and operating temperature every time the compressor starts and stops. This thermal cycling causes the flange assembly to expand and contract. A gasket material with poor creep relaxation will progressively lose the bolt load that keeps it compressed between the flange faces, reducing sealing margin over time. Recovery — the ability to spring back after compression — is also relevant: a material that permanently deforms under initial bolt load may not maintain contact as the joint moves thermally. These two properties, creep relaxation and recovery, are among the most important indicators of long-term sealing performance in thermally cycled applications.
Does refrigerant type affect gasket material selection?
Yes. Different refrigerants have different chemical properties and interact with gasket binder materials differently. HFC refrigerants, HFO refrigerants, ammonia (R717) and carbon dioxide (R744) each place different demands on the rubber binder component of a compressed fibre gasket. No binder material is universally compatible with all refrigerant compounds. The chemical resistance of the specific gasket grade to the refrigerant in service should be confirmed from the material supplier's chemical resistance data before specifying — particularly for ammonia, CO2 and newer HFO compounds where compatibility is more specific.