Rotary Seals for Food & Pharma: Sanitary Considerations

This article provides a practical, evidence-based guide to selecting and applying rotary seals in food and pharmaceutical (food & pharma) processing equipment with a focus on sanitary design. It covers regulatory drivers, material selection (elastomers, PTFE, perfluoroelastomers), clean-in-place (CIP) and sterilize-in-place (SIP) compatibility, design features that reduce contamination risk, validation and maintenance best practices, and actionable selection criteria to help engineers, QA specialists and procurement teams minimize microbiological and particulate risks while maximizing seal life. Key references include regulatory texts and hygienic design guidance from agencies such as the U.S. Food and Drug Administration and the European Hygienic Engineering & Design Group.

Why hygienic design matters in food & pharma

Contamination pathways: what rotary seals must prevent

Rotary seals on mixers, pumps, homogenizers and filling machines are dynamic sealing interfaces where product, cleaning fluids and environmental air meet rotating shafts. If a seal fails or has inappropriate geometry, common contamination pathways arise: leakage of product to bearing areas, entrapment of residues in crevices, and formation of biofilm on rough or damaged surfaces. These pathways increase risk of spoilage, cross-contamination, and product recalls. Using the correct rotary shaft seals and minimizing dead-legs are essential to prevent microbial ingress and particle shedding.

Regulatory and customer requirements

Food and pharma manufacturers must meet legal and customer requirements for materials in contact with product and for hygienic equipment design. In the EU, Regulation EC No 1935/2004 sets general rules for materials intended to contact food. In the US, the FDA provides guidance on food contact substances. For pharmaceutical applications, biocompatibility and extractables/leachables are assessed under standards such as USP and ISO series (e.g., ISO 10993) and GMP guidelines. Customers increasingly require documented evidence that rotary seals are made from food-grade or pharmaceutical-grade materials, are traceable, and compatible with CIP/SIP cycles.

Material selection for rotary seals

Elastomers vs. PTFE and perfluoroelastomers

Material choice is the single most important sanitary consideration for rotary seals. Elastomers (NBR, FKM, EPDM, silicone) offer flexibility and resilience for shaft movement, but vary in chemical and temperature resistance. PTFE and filled PTFE (e.g., bronze-filled, carbon-filled) are chemically inert and non-stick, reducing residue build-up, but have lower elasticity and require supportive seal designs (e.g., spring-energized face seals or composite PTFE lips). Perfluoroelastomers (FFKM) provide exceptional chemical and high-temperature resistance for aseptic processes where cost can be justified. For many food & pharma rotary applications, combinations—such as PTFE sealing lip on an elastomer energizer—provide a balance of low friction, low particle generation and adequate sealing force.

Temperature, chemical and sterilization resistance

Choose materials compatible with expected process temperatures and sterilization methods. CIP uses caustic and acidic detergents at moderate temperatures; SIP uses steam or hot water, sometimes at >121°C. Table 1 summarizes typical temperature ranges and CIP/SIP suitability for common seal materials; use it as a starting point but always confirm with manufacturer data sheets and validation testing.

Sources for general material ranges include manufacturer datasheets and material references such as O-ring and elastomer references. Always validate with specific compound data and perform extractables/leachables testing for pharma contact.

Design and installation best practices

Minimize crevices and use hygienic geometries

Hygienic rotary seal design reduces dead volume where product may collect. Use shaft housings with smooth transitions, radiused corners, and accessible gland seals. Where possible, prefer cartridge-style rotary seals or face seals designed for quick inspection and replacement. For aseptic product zones, design double-seal arrangements with barrier flushing (weep or pressurized barrier fluid) to protect the primary seal from product exposure.

CIP and SIP: implementation details for rotary interfaces

CIP and SIP impose mechanical and chemical stresses on rotary seals. Key considerations include: adequate surface finish (Ra) on shafts and seal seats to reduce wear and particle generation; correct gland lubrication or barrier fluids that are food-grade; and allowable rotational speeds and shaft eccentricity. The European Hygienic Engineering & Design Group (EHEDG) provides guidance on hygienic design and cleaning validation for equipment. Design options that aid CIP/SIP include flush ports, drainability, and selection of non-porous materials that resist biofilm formation.

Testing, validation and maintenance

Biocompatibility, extractables and leachables

For pharmaceutical contact, rotary seals must be qualified through biocompatibility and extractables/leachables (E&L) studies per USP and ICH guidelines. For food contact, migration testing and declarations of compliance (e.g., FDA food contact or EU declarations per EC No 1935/2004) are typical. Work with suppliers to obtain material certificates, formulation declarations, and test data. Where critical, require lot-traceability and validation samples for E&L testing in your specific process stream.

Inspection intervals and predictive maintenance

Define inspection intervals based on operating hours, temperature cycles, and observed wear modes. Typical checks include visual inspection for cracking, hardness testing of elastomers, monitoring torque/drive load changes, and leak detection. Implement predictive maintenance using historical failure data; for example, seal life in aggressive CIP/SIP environments may be primarily limited by thermal degradation rather than mechanical wear. Keep spare rotary seals in controlled storage (temperature/UV) to preserve material properties.

Practical selection checklist and common trade-offs

Selection checklist

• Identify product contact zone and required cleanliness class (food grade vs. aseptic pharma).
• List process chemicals, CIP detergents, and SIP temperatures and cycle durations.
• Specify shaft speed, eccentricity limits, and pressures.
• Select materials with proven CIP/SIP compatibility and regulatory support (FDA/EU/USP certificates).
• Design gland/housing for drainability and minimal dead volume; consider cartridge rotary seal systems for serviceability.
• Plan validation: microbial challenge (if aseptic), E&L tests, and accelerated aging.

Common trade-offs

Low-friction PTFE options minimize particle generation and residue adhesion but often cost more and require supportive energizer systems. Elastomers are economical and forgiving on shaft misalignment but can swell, harden, or degrade under aggressive chemicals or high-temperature steam. FFKM gives the best chemical/thermal profile but at significantly higher cost; use it where process purity justifies the expense (e.g., critical pharmaceutical filling lines).

Polypac: capabilities for sanitary rotary sealing solutions

Polypac is a scientific and technical hydraulic seal manufacturer and oil seal supplier specializing in seal production, sealing material development, and customized sealing solutions for special working conditions. Founded in 2008, Polypac began by manufacturing filled PTFE seals (including bronze-filled PTFE, carbon-filled PTFE, graphite PTFE, MoS2-filled PTFE, and glass-filled PTFE). Today, Polypac's product range includes O-rings made from NBR, FKM, silicone, EPDM and FFKM, as well as bespoke rotary seals designed for hygienic applications.

Polypac's custom rubber ring and O-ring factory covers more than 10,000 square meters with 8,000 square meters of factory space. Production and testing equipment are among the most advanced in the industry, and Polypac maintains long-term collaboration with numerous universities and research institutions domestically and internationally. These partnerships support material development (e.g., low-extractable elastomer formulations) and advanced testing such as accelerated aging, E&L screening, and tribology testing for rotary interfaces.

Key Polypac product strengths relevant to food & pharma sanitary seals:

• Material variety: filled PTFE, FFKM, silicone and food-grade elastomers for CIP/SIP compatibility
• Custom designs: cartridge rotary seals, face seals with PTFE lips, dual-seal arrangements with barrier flushing
• Quality & traceability: material certificates, batch traceability, and cooperation on validation protocols
• Testing capability: torque/friction testing, accelerated thermal aging, and contact compatibility studies

Polypac's main sanitary sealing products include: O-Rings, Rod Seals, Piston Seals, End Face Spring Seals, Scraper Seals, Rotary Seals, Back-up Rings, and Dust Rings. For projects that require sanitary-grade rotary seals, Polypac can provide material recommendations, prototype runs, and technical support for CIP/SIP validation.

FAQs

1. What is the best material for rotary seals in CIP/SIP environments?

There is no single 'best' material; selection depends on temperature, chemical exposure and application specifics. PTFE and FFKM provide superior chemical and thermal resistance for repeated CIP/SIP cycles; EPDM performs well for steam and alkaline cleaning in aqueous processes; silicone is useful for thermal tolerance but may have mechanical wear trade-offs. Always validate materials under your exact CIP/SIP profile.

2. Can I retrofit existing equipment with sanitary rotary seals?

Often yes. Retrofits should address not only the seal lip material but also gland geometry, surface finish and drainability. Cartridge seals or custom housings can simplify retrofits and improve hygienic performance. Work with a supplier to evaluate shaft runout, gland clearance and housing modifications.

3. How do I validate seals for pharmaceutical aseptic contact?

Validation typically includes material certificates (USP/ISO), extractables & leachables testing tailored to your formulation, biocompatibility if relevant, and sterile process qualification (e.g., microbiological challenge or media fill where applicable). Engage your regulatory/QC team early and collaborate with seal suppliers on documentation.

4. How long should rotary seals last under CIP/SIP?

Service life varies widely: some seals last months under aggressive CIP/SIP and high mechanical stress, while others last years in gentler operations. Factors include material, surface finish, shaft alignment, and operating temperature. Implement condition-based inspections and maintain spare inventory with controlled storage.

5. Are PTFE seals prone to extrusion or leakage compared to elastomers?

Pure PTFE has low elasticity and can be more sensitive to extrusion under pressure. That is why many PTFE-based solutions use energized designs (elastomer energizers or spring-energized PTFE face seals) or back-up rings to prevent extrusion and ensure consistent sealing under pressure and shaft motion.

6. Where can I find certified food-grade seals and documentation?

Reputable suppliers provide certificates of conformity to FDA or EU regulations, raw material declarations, and sometimes specific testing reports. For pharmaceutical uses, request USP-related documentation and E&L studies. Polypac supplies material certificates and supports validation documentation for its seal products.

If you need assistance in selecting rotary seals for a specific food or pharmaceutical application, request a technical consultation or product samples. Contact Polypac to discuss custom sanitary sealing solutions, material validation, and prototype runs. For product inquiries and technical support, visit Polypac's product pages or contact their sales engineers for tailored recommendations and testing assistance.

For product details, technical datasheets, or customized sanitary rotary seal solutions, contact Polypac's technical team to request drawings, material certificates, and validation support.

References and further reading: FDA food contact guidance (fda.gov); EC No 1935/2004 (eur-lex.europa.eu); EHEDG hygienic design guidance (ehedg.org); general material information (PTFE, O-ring).