Selection Principles for Valve Soft Seal Materials: PTFE, NYLON, PEEK

Valve soft seal materials PTFE (Polytetrafluoroethylene), NYLON (Polyamide), and PEEK (Polyetheretherketone) have distinct differences in temperature resistance, chemical compatibility, pressure resistance, and wear resistance. The selection shall be based on core working conditions such as medium type, operating temperature, pressure level, and service life requirements. The following are the detailed selection principles and comparative analysis.

1. PTFE (Polytetrafluoroethylene) Soft Seal Selection Principles

1.1 Core Adaptation Conditions

Temperature Range: Continuous operating temperature -196℃~260℃; suitable for both ultra-low temperature and high-temperature scenarios, with excellent thermal stability.
Chemical Compatibility: Known as "the king of corrosion resistance", it is compatible with almost all chemical media (acids, alkalis, oxidants, organic solvents, etc.), except for molten alkali metals and fluorine gas at high temperatures.
Pressure Resistance: Suitable for low to medium pressure conditions; for small-diameter valves (DN15~DN50), the maximum working pressure is PN16~PN40; for large-diameter valves (DN65 and above), it is recommended to use PN10~PN16 to avoid seal deformation.

1.2 Preferred Application Scenarios

- Corrosive medium transportation: Chemical industry (strong acids, strong alkalis, organic solvents), pharmaceutical industry (corrosive APIs), and wastewater treatment (acidic/alkaline wastewater).

- Ultra-low temperature or high-temperature scenarios: Cryogenic fluid pipelines (-196℃~-50℃) and high-temperature fluid pipelines (150℃~260℃) that do not require high pressure resistance.

- Food and beverage industry: Complies with FDA standards, suitable for food-grade fluid transportation (e.g., fruit juices, dairy products) with low friction and no pollution.

1.3 Limitations and Prohibited Scenarios

- Poor wear resistance: Not suitable for media containing solid particles (e.g., slurry, powder) or high-frequency opening and closing scenarios (service life ≤50,000 cycles).

- Low creep resistance: Easily deforms under long-term high pressure and high temperature, so it is prohibited to use in high-pressure large-diameter scenarios (DN200 and above, PN40 and above).

- High-temperature molten alkali metals and fluorine gas environments are prohibited.

2. NYLON (Polyamide) Soft Seal Selection Principles

2.1 Core Adaptation Conditions

Temperature Range: Continuous operating temperature -40℃~120℃; short-term maximum temperature ≤150℃; poor high-temperature resistance, easy to age when exceeding 120℃ for a long time.
Chemical Compatibility: Compatible with non-corrosive media such as water, oil, and neutral aqueous solutions; incompatible with strong acids, strong alkalis, and polar organic solvents (e.g., methanol, acetone), which can cause swelling and dissolution.
Pressure Resistance: Suitable for low-pressure scenarios; maximum working pressure PN10~PN25, applicable to small to medium-diameter valves (DN15~DN100).
Wear Resistance: Excellent self-lubrication and wear resistance, suitable for media with a small amount of fine particles (e.g., clean water with slight sediment).

2.2 Preferred Application Scenarios

- General water supply and drainage: Tap water pipelines, domestic sewage pipelines, and irrigation systems (low pressure, room temperature).

- Oil and lubricating oil transportation: Mechanical equipment oil circuits, hydraulic systems, and fuel pipelines (non-corrosive oil media).

- Low-cost and general-purpose scenarios: Civil construction, general industrial pipelines with low requirements for temperature and pressure, and pursuit of cost-effectiveness.

2.3 Limitations and Prohibited Scenarios

- Prohibited in corrosive media (strong acids, strong alkalis, organic solvents) to avoid material failure.

- Prohibited in high-temperature scenarios (above 120℃) and high-pressure scenarios (above PN25) to prevent deformation and aging.

- Not suitable for media with a high content of solid particles (e.g., slurry, ore pulp) to avoid excessive wear.

3. PEEK (Polyetheretherketone) Soft Seal Selection Principles (Supplemented and Integrated)

3.1 Core Adaptation Conditions (Key Summary)

Temperature Range: Continuous operating temperature -20℃~260℃; short-term peak temperature ≤300℃; better high-temperature stability than PTFE and NYLON.
Chemical Compatibility: Compatible with petroleum products, acid-base solutions (pH1~14), organic solvents, and water; incompatible with strong oxidizing media (e.g., concentrated nitric acid, liquid chlorine).
Pressure Resistance: Wide pressure adaptation range; small-diameter valves (DN15~DN50) can reach PN100, medium-diameter valves (DN65~DN200) PN16~PN40, and large-diameter valves (DN250 and above) PN10~PN16 (see the previous pressure resistance chart for details).
Comprehensive Performance: Excellent mechanical strength, wear resistance, and dimensional stability; modified PEEK (carbon fiber/glass fiber reinforced) can further improve pressure resistance and wear resistance.

3.2 Preferred Application Scenarios (Key Summary)

- High-temperature and high-pressure industrial pipelines: Petrochemical industry (crude oil, chemical raw materials), power industry (steam, hot water), and high-pressure hydraulic systems.

- Food and pharmaceutical industry: Food-grade and pharmaceutical-grade fluid transportation (complies with FDA 21 CFR 177.2600 standard), with no pollution and high safety.

- Harsh working conditions: High-temperature, high-pressure, and corrosive (excluding strong oxidants) scenarios that require long service life (opening and closing life ≥100,000 cycles).

3.3 Limitations and Prohibited Scenarios (Key Summary)

- Prohibited in strong oxidizing media (e.g., concentrated nitric acid, liquid chlorine) to avoid material oxidation and degradation.

- Not recommended for high-pressure and large-diameter scenarios (DN250 and above, PN65 and above); metal hard seals are preferred.

4. Comparative Selection Table of Three Soft Seal Materials

Performance Indicator	PTFE	NYLON	PEEK	Priority Selection Suggestion
Continuous Temperature Resistance	-196℃~260℃	-40℃~120℃	-20℃~260℃	Ultra-low temperature: PTFE; High temperature (≤260℃): PTFE/PEEK; Room temperature: NYLON
Chemical Corrosion Resistance	Excellent (almost all media compatible)	Poor (only non-corrosive media)	Good (excluding strong oxidants)	Strong corrosion: PTFE; Non-corrosion: NYLON; General corrosion: PEEK
Maximum Pressure (DN15~DN50)	PN16~PN40	PN10~PN25	PN16~PN100	High pressure: PEEK; Medium pressure: PTFE; Low pressure: NYLON
Wear Resistance	Poor	Good	Excellent (modified better)	Particulate media: PEEK (modified); Slight particles: NYLON; Clean media: PTFE
Cost	Medium	Low	High	Cost-sensitive: NYLON; Balanced cost-performance: PTFE; High-performance requirements: PEEK
Service Life (Opening and Closing Cycles)	≤50,000	50,000~80,000	≥100,000	Long service life: PEEK; General requirements: NYLON/PTFE

5. General Selection Flow

Clarify core working conditions: Medium type (corrosive/non-corrosive/particulate), operating temperature, and pressure level.
Eliminate incompatible materials based on chemical compatibility and temperature resistance.
Screen materials based on pressure resistance and diameter requirements.
Balance cost and service life requirements to determine the final material.
Verify with manufacturer's test reports (sealing performance, life test, etc.) to ensure compliance.