mechanical seal material

How to Choose the Right Mechanical Seal Material

More seals fail from the wrong material than from any design flaw. Choosing the right mechanical seal material is really two decisions — the hard-and-soft face pair that runs together, and the elastomer that seals the static gaps — and both come down to one question: what fluid, at what temperature, is this seal living in?
Get those two right and the seal has a fighting chance. Here’s how to make each choice.

Choosing the face materials

The faces are where friction, heat and wear happen, so the mechanical seal face material carries the load. Almost every seal pairs a soft face against a hard one:
  • Carbon-graphite (soft): low friction, self-lubricating, ideal against a hard face on clean fluids. The default soft face.
  • Silicon carbide, SiC (hard): extremely hard and chemically stable — the go-to for abrasives, chemicals and high speed.
  • Tungsten carbide, TC (hard): tough and impact-resistant for heavy-duty service; denser than SiC.
mechanical seal material
  • Ceramic / alumina (hard): a budget hard face for clean water and general duty.

The two rules worth memorising: carbon versus SiC for clean liquids, and SiC versus SiC when abrasives are present. Carbon can’t survive grit; two hard faces can.

Choosing the secondary seal (elastomer)

The O-rings or bellows around the faces have to resist the same fluid the faces see. This is straight elastomer chemistry — the same logic as any O-ring or rubber sheet:

Elastomer Best for Avoid with
NBR (nitrile) Oil, water, general duty to ~100°C Strong chemicals, high heat
EPDM Hot water, steam, many chemicals Oils & fuels
Viton / FKM Oils, fuels, high temperature Some ketones/amines
PTFE Aggressive chemicals, wide temp (Hard; needs spring energising)

Put the two together

A worked example: for a hot caustic solution you might pick SiC versus SiC faces with EPDM secondaries; for a diesel transfer pump, carbon versus SiC with Viton; for an abrasive slurry, SiC versus SiC with a suitable flush. The face pair handles the mechanical duty; the elastomer handles the chemistry. When they disagree — abrasive and aggressive at once — go hard on both.

The mistake that wastes good material

Even the perfect mechanical seal material fails if the faces run dry or too hot, so material selection and the flush plan have to be decided together. SiC tolerates far more heat than carbon, but no face survives dry running indefinitely. The other frequent error is choosing the elastomer for the process fluid but forgetting the barrier or flush fluid it also contacts on a double seal — both have to be compatible. Think of the material choice as covering every fluid the seal touches, not just the one being pumped.

Frequently Asked Question

There’s no single best — carbon vs SiC suits clean fluids, SiC vs SiC suits abrasives and chemicals, tungsten carbide suits heavy impact duty. Match the pair to the fluid and speed.

NBR for oil and general water, EPDM for hot water and many chemicals (never oil), Viton for oils and heat, PTFE for aggressive chemicals. It follows the same rules as any seal elastomer.

faces and elastomers — to your fluid and temperature. Send the details and we’ll specify the pair; our complete mechanical seal guide covers the wider selection.

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