What volume swell is acceptable for an elastomer seal?

Keep combined volume swell at or below 20%. Swell from 10% to 20% is workable with a wider gland, but above 20% the compound is considered incompatible and the seal will extrude or take a permanent set.

How does temperature change elastomer swell?

Thermal volumetric expansion adds to fluid swell: ΔV/V = 3·α·ΔT, where α is the linear expansion coefficient. A compound at 250 °F above a 70 °F reference gains several percent of thermal swell on top of its fluid swell.

Which elastomer resists Skydrol and phosphate-ester fluids?

EPDM and PTFE resist Skydrol and phosphate esters, while nitrile and fluorocarbon swell heavily. For aviation hydraulic service, EPDM is the standard choice; PTFE is used where near-zero swell is required.

Is PTFE compatible with Phosphate Ester?

At 70 °F PTFE swells 2.0% in Phosphate Ester, rated excellent. Combined with thermal swell at 200 °F the total is 4.9%, within the 20% service limit.

What temperature range does PTFE cover?

Polytetrafluoroethylene runs continuously from -100 to 500 °F. At 200 °F it is inside that range.

How much does PTFE soften in Phosphate Ester?

The 4.9% combined swell softens PTFE by about -1.7 Shore A, from 70 to 68.3 Shore A. A shift beyond ±10 Shore A signals the compound is over-swelling.

PTFE vs Phosphate Ester Compatibility

Volume swell, hardness shift and temperature range for Polytetrafluoroethylene (PTFE) in Phosphate Ester.

PTFE in Phosphate Ester

Polytetrafluoroethylene (PTFE) in Phosphate Ester swells 2.0% at 70 °F. At a 200 °F service temperature the thermal term adds 2.9%, for a combined 4.9% swell and a -1.7 Shore A hardness shift to 68.3 Shore A. The compound's continuous range is -100 to 500 °F.

Volume swell and hardness change

Volume swell and hardness change is computed deterministically from the parameters encoded in this page's address, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Service temperature and extrusion limit

Service temperature and extrusion limit is computed deterministically from the parameters encoded in this page's address, so the same inputs always produce the same result and the same OAS-XXXX verification hash.

Worked example

Immerse PTFE in Phosphate Ester at 200 °F against a 70 °F reference.

Worked example steps for this calculation
Step	Formula	Value
Fluid swell	ΔV_fluid at 70 °F	2.0 %
Thermal swell	ΔV/V = 3·α·ΔT	2.9 %
Combined swell	ΔV = ΔV_fluid + ΔV_thermal	4.9 %
Hardness shift	ΔH ≈ −0.35 · ΔV	-1.7 Shore A

PTFE reaches 4.9% combined swell in Phosphate Ester at 200 °F, inside the 20% service ceiling, with a resulting hardness of 68.3 Shore A.

Export this calculation

OAS-8090

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Engineering summary

Governing parameters and computed results for PTFE vs Phosphate Ester Compatibility.

Governing parameters and computed results for this calculation
Parameter	Value
Compound	PTFE
Fluid	Phosphate Ester
Thermal Volumetric Expansion	0.00 %
Combined Volume Swell	2.00 %
Hardness Change	-0.7 Shore A
Resulting Hardness	69.3 Shore A
Allowable Extrusion Gap	3.60 mil
Extrusion Check	Fail — 4.00 > 3.60 mil

Frequently asked questions

Is PTFE compatible with Phosphate Ester?: At 70 °F PTFE swells 2.0% in Phosphate Ester, rated excellent. Combined with thermal swell at 200 °F the total is 4.9%, within the 20% service limit.
What temperature range does PTFE cover?: Polytetrafluoroethylene runs continuously from -100 to 500 °F. At 200 °F it is inside that range.
How much does PTFE soften in Phosphate Ester?: The 4.9% combined swell softens PTFE by about -1.7 Shore A, from 70 to 68.3 Shore A. A shift beyond ±10 Shore A signals the compound is over-swelling.

Elastomer Compatibility & Swell Analyzer

Deterministic chemical compatibility, thermal expansion and volume swell for twelve elastomer compounds across fifteen industrial fluids.

Result

PTFE in Phosphate Ester swells 2.0 % at 70 °F, shifting hardness by -0.7 Shore A.

2.0% swell

Compound & Fluid

Elastomer Compound

Industrial Fluid

Operating Conditions

Operating Temperature

°F

Durometer (Shore A)

Shore A

Typical range 55–70 Shore A

System Pressure

psi

Diametral Clearance

Metal-to-metal gap across the seal.

Compatibility Rating

Excellent2 % reference swell at 70 °F, 70 h immersion

Service range -100–500 °F · 8 % compression set · cost index 6.0