10 Considerations When Selecting Plastic Materials for Valve Seats and Seals

Selecting the right plastic materials for valve seats and seals is critical to ensure the reliability and long service life of a valve.
This is particularly important for valves used in industries such as aerospace, medical, and semiconductor where failure of the polymer can have catastrophic results.

When working with valve engineers, plastics that have the following 10 performance characteristics are often required for a successful design.

1. A “Goldilocks” Compressive Modulus

The plastic needs to be soft enough to conform to mating metal surfaces and yet stiff enough to seal a pressurized process fluid. It is important that the plastic maintain its modulus within an acceptable range throughout the operating temperature range of the valve.

2. A Low Coefficient of Friction (COF)

If the plastic component will be in sliding contact with a metal surface when the valve is actuated, the sliding pairs must have a low enough COF to achieve the desired actuation torque. Plastics are available with additives such as PTFE, graphite, and molybdenum disulfide to reduce friction under certain conditions.

3. Good Creep and Stress Relaxation Characteristics

The polymer must be able to maintain apparent stress and resist creep strain to effectively seal over long periods of time.

4. Ductility Throughout the Operating Temperature Range

The plastic must exhibit sufficient ductility, especially in cold temperatures or at high strain rates where some polymer materials become brittle.

5. Resistance to Degradation from the Process Fluid

The plastic must resist chemical attack and environmental stress cracking when exposed to the process fluid. It must also resist degradation from any chemicals such as cleaners that the valve might encounter during service.

6. Will not Contaminate the Process Fluid

The plastic won’t leach or outgas chemicals that might contaminate the process fluid.

7. Flammability Characteristics

For valves that control the flow of flammable materials, the plastic may need to have certain flammability characteristics such as having a minimum LOI (limiting oxygen index) or a certain level of resistance to impact ignition.

8. Fatigue Resistance

The plastic needs to have good fatigue resistance so that it can withstand the cyclic stresses associated with repeated actuations.

9. Certifications

For certain industries such as food processing, the polymer may need to comply with industry standards such as FDA, ISO, or USP.

10. Cost

The polymer used for the seals must have a price point that makes it a practical choice for the valve.

For additional information about polymer selection for valves, watch Curbell Plastics’ webinar Choosing Plastic Materials for Use in High Performance Valves and Regulators.

To learn about top performing materials for valve seats and valve seals visit our valves, regulators, and seals industry page. For material questions call 1-800-553-0335 or contact us.