PTFE Rotary Shaft Seals
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Pressure Cycling and Pulsation Issues in Polymer Seals

Pressure cycling and pulsation can lead to seal issues like extrusion, blow-by, and fatigue damage. There are, however, some design principles that can address these issues and mitigate their effects. This article takes a look at the issues related to cycling and pulsation and addresses six key design considerations related to them.

Pressure Cycling and Pulsation

Pressure cycling refers to repeated transitions between low and high pressure, including dwell time at each level. Pulsation, on the other hand, is associated with high-frequency pressure oscillations superimposed on the mean system pressure (often pump- or compressor-driven). Pressure spikes are short-duration transients that exceed nominal operating pressure.

Designing polymer seals for cyclic pressure and pulsation is actually a system-level problem. Consideration must go into the material, energization method, gland geometry, hardware stiffness, surface finish, and validation testing.

Seal Issues Related to Pressure Cycling and Pulsation

When polymer seals are subject to pressure cycling and pulsation, the primary design objective becomes the ability to maintain adequate contact stress and sealing integrity throughout the entire pressure waveform while avoiding extrusion, blow-by, and fatigue damage.

Extrusion occurs when the seal is forced into a clearance gap by pressure, like a soft solid getting pushed into a narrow crack. Blow-by takes place when a pressurized fluid or gas leaks past the seal because there is not enough contact stress. Fatigue damage is the progressive cracking or material breakdown that is caused by repeated loading cycles. Note that each individual cycle can be below the material’s one-time strength limit and still result in fatigue damage.

Signs of Pressure Cycling and Pulsation Issues

There are several signs that pressure cycling and pulsation are causing problems. One of the first is early leakage after a very short run-in period. The seal might also experience intermittent leakage that is related to the duty cycle or pump frequency. Another sign of seal problems is the extrusion of the gear lip, torn edges, or nibbling. Finally, backup ring displacement or seal rotation can also be a signal of issues. 

These problems usually show up in hydraulic actuators, pumps, and manifolds, gas compression stage and valve plates, chemical processing skids with pulsation dampeners, and high-cycle test equipment and aerospace pneumatic systems.

Design Tips for Addressing Pressure Issues

Here are some design tips for working with seals undergoing pressure cycling.

Pressure Waveform

In order to mitigate issues with pressure cycling and pulsation, it is important to look at the pressure waveform and not just the peak pressure. For example, document mean pressure, peak pressure, minimum pressure, ramp rate, frequency, and dwell times. Then identify the transient spikes separately from the steady cycles. Once this information has been gathered, map the waveform to the duty cycle and the total number of cycles.

Polymer

Remember to select the polymer family for the seal based on cyclic strength and creep resistance. Filled PTFE offers good creep resistance and extrusion margin. PEEK and PPS options can lead to a higher modulus, better load retention, and improved wear. UHMW-PE offers low friction but lower stiffness. However, keep in mind that the material choice should also be considered with regard to the temperature, media, PV, and allowable deformation.

Spring-Energized Seals

Another excellent option is to utilize spring-energized seals to maintain contact stress when system pressure drops. These seals have pressure-energized lips designed to avoid issues during pressure reversals. In addition, consider the use of dual-acting geometries for bidirectional pressure. And avoid relying solely on squeeze for long-life high-cycle conditions when relaxation is expected.

Seal Gland

When designing the gland, it is important to ensure that the seal is both well-supported and deforms in a controlled manner when subjected to pressure cycling. The compressive fa orce should provide reliable initial sealing force without being so high that excessive creep results over time. Utilize radii and lead-in chamfers to eliminate sharp edges that can result in problematic notches or tears. And when clearances cannot be held tightly, use anti-extrusion features to ensure the pressure cannot force the polymer into a gap.

Backup Ring

Another potential aspect of the design is the use of a backup ring. Its material should be fully compatible with the primary seal and can maintain strength and dimensional stability across the operating temperature range. When deciding between split or solid design backup rings, keep in mind potential issues with rotation and migration during pressure pulsation. 

Surface Finish

Under pressure cycling, the surface and interface details matter significantly. Small leak paths are the potential problems here, and can be addressed. First, the counterface roughness should result in a surface that supports film formation but does not lead to bypass channels or issues with abrasive wear. The lay direction should prevent machining grooves from behaving as micropumps during pressure fluctuations. In addition, if there is a possibility that erosion, wear, or corrosion could affect the roughness over time, use coatings or surface treatment that will stabilize the counterface.

Conclusion

Pressure cycling and pulsation can cause extrusion, blow-by, and fatigue damage. Careful design, however, can mitigate these issues.

If you are working on a seal design that must provide reliable performance when subject to pressure cycling and pulsation, let the polymer seal experts at Advanced EMC help. Contact us today.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

How PTFE and PEEK Enable Reliable Sealing Across Extreme Media

In the world of advanced sealing, few materials can match the resilience and versatility of PTFE and PEEK. When systems operate at temperatures below –200 °C or handle chemicals capable of dissolving most polymers, seal failure is not an inconvenience—it’s a critical risk. In such environments, the combination of PTFE and PEEK enable reliable sealing performance that remains stable, predictable, and long-lived.

This blog post focuses on key features of PTFE and PEEK that make their sealing solutions a good choice for extreme media and reviews applications where these materials excel.

The Challenge of Sealing Across Opposing Extremes

Designing a seal for cryogenic and/or corrosive service is an exercise in contradiction. At extremely low temperatures, most polymers become brittle and lose their ability to conform to mating surfaces. Under high heat or chemical exposure, others swell, creep, or break down at the molecular level. Even metals typically  lack the elasticity or chemical resistance required for tight dynamic sealing.

True reliability comes from materials that can maintain their properties across this spectrum—retaining flexibility near absolute zero while withstanding oxidative and acidic environments at elevated temperatures. This is precisely where PTFE and PEEK excel.

PTFE: The Chemical Inertness Benchmark

Polytetrafluoroethylene (PTFE) serves ast the industry standard for chemical resistance and thermal stability. With its fully fluorinated carbon chain forms, PTFE is one of the most inert polymer molecular structures known. It is impervious to nearly all solvents, acids, and bases. Its operating range is from –250 °C to +260 °C, and PTFE is able to maintain low friction and minimal surface adhesion even in the harshest conditions.

In dynamic seals, its extremely low friction and self-lubrication allows results in lower torque, reduced stick-slip, and minimal wear against counterfaces. In addition, cryogenic engineers value PTFE’s ability to retain elasticity at temperatures that render most elastomers and many polymers extremely brittle. In chemical processing, it functions as a barrier material, protecting metallic components from corrosive attack.

However, unfilled PTFE has its limits. Under continuous load, it can creep or cold-flow, gradually losing preload. Engineers address this with fillers such as glass, graphite, carbon, or bronze, with each improving compressive strength and wear resistance. These modifications allow PTFE and PEEK enable reliable sealing designs to meet performance expectations in applications ranging from cryogenic valves to aggressive chemical reactors.

PEEK: Structural Integrity Under Pressure

Polyether ether ketone (PEEK) seems to complement the properties PTFE by offering exceptional mechanical strength and outstanding dimensional stability. Where PTFE provides chemical inertness, PEEK contributes structural endurance. Its semi-crystalline molecular structure gives it tensile strengths exceeding 90 MPa and excellent creep resistance maintained even at continuous temperatures approaching 250 °C.

In sealing systems, PEEK often serves as a backup ring, retaining element, or structural carrier for softer sealing materials. PEEK is excellent at resisting extrusion under high differential pressure and maintains shape when thermal cycling could otherwise deform conventional polymers. Chemically, PEEK withstands regular exposure to hydrocarbons, steam, and strong acids, thus making it indispensable in oil-and-gas and chemical processing environments.

Composite grades filled with carbon fiber, graphite, or PTFE further optimize tribological performance. These blends combine the toughness of PEEK with the low friction and self-lubrication of PTFE, thus ensuring smoother operation dynamic sealing solutions where where friction is critical.

PTFE and PEEK Performance Across Extreme Temperatures and Corrosive Media 

Engineers often use PTFE sealing solutions for operations that involve components, such as cryogenic hydrogen and oxygen valves, where lubrication must persist without freezing or outgassing. On the other hand, PEEK components dominate in high-temperature pumps and compressors exposed to sour gases, acids, or amine-laden fluids. 

Even in vacuum environments, PTFE’s extremely low outgassing helpts to ensure critical contamination-free operation. PEEK’s dimensional stability supports precise alignment and positioning even over extreme temperature ranges. Such mechaniacl properties can translate into longer service life, reduced maintenance cycles, and measurable operational cost savings, all of which are outcomes every engineer values.

Conclusion: Material Science at the Edge of Performance

When the operating conditions involve everything form cryogenic cold to corrosive heat, only a select group of polymers can deliver consistent performance: PTFE and PEEK. One offers unmatched chemical inertness and low friction; the other, exceptional mechanical integrity and pressure resistance. Working independently or in tandem, PTFE and PEEK enable reliable sealing in systems where failure is simply not an option.

For engineers designing valves, compressors, or actuators expected to survive the extremes, these two polymers represent more than material choices—they represent confidence. Through advanced formulations, precision machining, and innovative hybrid geometries, the limits of polymer sealing continue to expand.