Gasket + O-Ring Material Reference

Why this matters

Wrong gasket material = leak. Buna-N in hot water heater = degraded in 6 months. EPDM in oil-exposure = swollen + ruined. Each rubber compound has specific chemical + temperature compatibility. Knowing which gasket works for which application prevents the leak callback. This is the field card.

Common gasket / o-ring materials

Buna-N (Nitrile, NBR)

• Most common general-purpose
• Good oil + fuel resistance
• Temp range: -40°F to 250°F
• Limited weathering (UV degrades)
• Black
• Cheap
• Use: hydraulics, fuel systems, oil, water (not hot)

EPDM (ethylene propylene)

• Excellent water + steam + weather
• Good UV resistance
• Temp range: -65°F to 300°F
• BAD with oil, fuel, hydraulics
• Black
• Use: outdoor weather seals, hot water, steam, brake fluid, glycol

Silicone

• Excellent temperature range
• Temp range: -75°F to 450°F (some +)
• Food-grade options
• Lower tensile strength
• Red, white, clear, OR translucent
• Use: high-temp applications, food + medical, sealing

Viton (FKM, fluoroelastomer)

• Premium high-temp + chemical-resistant
• Temp range: -15°F to 400°F+
• Excellent fuel + oil + chemical resistance
• Expensive
• Brown OR green typically
• Use: refrigerant lines, high-temp seals, aggressive chemicals

Neoprene (CR)

• Good general-purpose
• Decent oil + chemical resistance
• Temp range: -40°F to 250°F
• UV resistant
• Black
• Use: general industrial, automotive, weather sealing

Cork

• Compressible, vibration-dampening
• Temp range: -40°F to 200°F
• Permeable; not for liquids
• Use: vibration mounting, gaskets where compression matters

Felt

• Soft, conformable
• Vibration dampening
• Some sealing function
• Use: bearings, dust seals, low-pressure applications

PTFE (Teflon)

• Chemical-resistant (most chemicals)
• Temp range: -100°F to 500°F
• Self-lubricating
• Brittle at very low temps
• White
• Use: chemical pipe sealing, high-temp/chem environments

Graphite

• Heat-resistant
• Compressible
• Chemical-resistant
• Black
• Use: industrial gasket sealing, flange gaskets

Compressed fiber (Manhauser, Klingerit)

• General industrial gasket sheet
• Various base materials
• Temp + chem range varies by grade
• Use: flange gaskets, plumbing, industrial

Asbestos (legacy, banned/regulated)

• Older industrial gaskets
• Excellent heat + chemical
• Health hazard
• Replace when discovered (asbestos abatement)

Application matrix

Water (residential)

• Buna-N OR EPDM
• EPDM for hot water
• Buna-N for cold water

Hot water + steam

• EPDM
• Silicone
• Viton for highest temp

Oil + hydraulic

• Buna-N (standard)
• Viton (premium)

Refrigerant (HVAC)

• Viton (excellent)
• Sometimes Neoprene
• DEFINITELY NOT EPDM (incompatible)
• Check refrigerant compatibility

Fuel (gasoline, diesel)

• Buna-N
• Viton (premium)
• Wear resistance OK

Brake fluid (DOT 3, 4)

• EPDM ONLY
• NOT Buna-N (swells)

Outdoor weather seals

• EPDM
• Neoprene
• Silicone

Chemical exposure (acids, bases)

• Viton
• PTFE
• Specific to chemical

High temperature (> 300°F)

• Silicone
• Viton
• PTFE

Food-grade

• NSF-rated silicone
• Specific food-grade compounds

Low-temp (sub-freezing)

• Buna-N down to -40°F
• Silicone to -75°F

O-ring sizing (AS568 standard)

Sizing:

• ID (inside diameter)
• Cross-section thickness
• AS568 numbered series (most common)

Common AS568 sizes:

Number	ID	Cross-section
010	1/4"	1/16"
013	1/2"	1/16"
110	1/4"	3/32"
210	1/2"	1/8"
218	1-1/4"	1/8"
327	2"	3/16"

Many more sizes; reference chart needed for specifics.

Gasket types

Cut sheet gasket

• Cut from sheet stock (felt, cork, neoprene, etc.)
• Use template
• Specific to flange

Pre-cut gaskets

• Manufacturer-specific (auto, OEM equipment)
• Match part number exactly

Spiral wound (industrial)

• Layered metal + filler
• High-pressure / high-temp
• Industrial / refining

Sheet gasket (full-face)

• Flat gasket covers entire flange face
• Bolt holes punched
• Standard plumbing

Ring gasket (raised face)

• Inside bolt circle only
• Industrial flanges

Cam profile gasket

• Specific industrial flange profile
• Compress + seal in one direction

Installation tips

Surface preparation:

• Clean both surfaces (no oil residue)
• Verify no scratches OR pitting where gasket sits
• Light sanding if surface rough

Gasket coating (sometimes):

• Manufacturer-specified gasket sealer
• Don't apply OEM gasket maker (RTV) on pre-formed gaskets
• Some gaskets self-sealing

Bolt torque:

• Per manufacturer spec
• Sequenced torque (cross pattern)
• Multiple passes increasing torque

No reuse (typically):

• Compressed gasket flat sealed once
• Replace when removed

O-ring installation

Lubricate (don't dry-install):

• O-ring lubricant (specific OR petroleum jelly OR refrigerant oil for HVAC)
• Reduces friction; prevents twist
• Helps seat properly

Avoid pinching:

• Insert into groove gently
• Use plastic tool if needed
• Damaged o-ring = leak

Verify size + cross-section:

• Wrong size won't seal
• Wrong material won't last

Common gasket mistakes

Wrong material: degrades fast.

Wrong size: doesn't seal.

Improper torque: too loose leaks; too tight crushes.

Reusing flattened gasket: don't seal twice.

No surface prep: dirt + oil = leak.

Wrong sealant on pre-formed gasket: prevents proper seal.

Cross-threading bolt: compresses unevenly.

Skipping sequence: torque cross-pattern, not in order.

When to replace

Visible signs:

• Hardening / cracking
• Compression set (permanent flat)
• Tears OR notches
• Discoloration
• Swelling (chemical attack)

Replace at:

• Every equipment service
• Whenever fitting opened
• Any leak

Truck stock

General O-ring kit (Buna-N, basic, 1/16" - 1/4" cross-section):

• AS568 sizes 004 - 240

Viton kit (HVAC + chemical):

• Higher cost
• Specific sizes for refrigerant work

Plumbing gaskets:

• Faucet gaskets
• Pipe flange gaskets
• Toilet wax ring / sponge ring

HVAC:

• Refrigerant flare gaskets
• Compressor service gaskets
• Various trade-specific

Material identification

Visually:

• Buna-N: black, slightly oily smell
• EPDM: black, dry feel
• Silicone: red/orange/clear OR white
• Viton: green/brown
• Neoprene: black, slightly tacky

Burn test (caution):

• Buna-N: black smoke, gasoline smell
• EPDM: black smoke, no chemical smell
• Silicone: white ash
• Viton: doesn't burn well

Better: read packaging + spec:

• "Nitrile" = Buna-N
• "EPDM," "EPR"
• "FKM," "Fluoroelastomer," "Viton"
• "VMQ" = Silicone

References

• ASTM D2000 (rubber spec)
• AS568 (o-ring sizes)
• SAE J515 (hydraulic seals)
• Parker O-Ring Handbook
• Manuall internal: Common Fittings Reference, Pipe Thread + Sealants