Selecting Wiper Rings for Food and Pharma Applications

This article explains how to select wiper rings for food and pharmaceutical applications with an emphasis on hygienic performance, chemical compatibility, regulatory compliance, and long-term reliability. It is written for engineers, procurement specialists, and QA/QC professionals responsible for selecting dynamic scraper seals in mixers, piston/rod applications, pump shafts, and hygiene-critical hydraulic systems. The guidance balances practical field experience with standards-based references so design choices are verifiable and auditable.

Sealing fundamentals for hygienic equipment

What is a wiper ring and why it matters

A wiper ring (also called a scraper seal or wiper seal) is a dynamic sealing element designed to prevent contaminants (dirt, process fluids, CIP residues) from entering a cylinder or bearing area and to retain lubrication where required. In food and pharma equipment the wiper ring's role expands: it must resist aggressive cleaning agents, avoid product contamination, and not shed particles or extractables that could compromise product safety. Wikipedia's overview of hydraulic cylinders summarizes common seal types and their functions, useful background when wiper rings are part of cylinder assemblies (Hydraulic cylinder - Wikipedia).

Functional differences: wiper ring vs rod seal vs lip seal

Wiper rings are typically located on the exterior side of a rod or shaft to scrape off contaminants before they reach the internal sealing system. Rod seals (primary dynamic seals) retain fluid under pressure. Lip seals (including static and dynamic variants) may be used for low-pressure scraping or secondary contamination control. Choosing a proper wiper ring reduces wear on rod seals and lowers maintenance frequency while improving product safety in hygienic zones.

Standards and traceability expectations

For food and pharma equipment, traceability and materials documentation are essential. While there is no single global standard exclusively for wiper rings, O-ring and elastomer standards such as ISO 3601 and material compliance frameworks (FDA food-contact regulations, USP Class VI for biological reactivity) provide the documentation approach QA teams require. See the FDA's Food Contact Substance page for regulatory context (FDA - Packaging & Food Contact Substances).

Material selection: compatibilities and regulatory considerations

Common materials used for wiper rings and their properties

Typical materials include NBR (nitrile), FKM (fluoroelastomer), EPDM, silicone, FFKM (perfluoroelastomer), and PTFE or filled PTFE compounds (bronze-filled, carbon-filled, MoS2-filled, glass-filled). Each material brings trade-offs in temperature range, chemical resistance, permeability, and particle-shedding behavior. For example, PTFE and filled PTFE offer extremely low extractables and excellent chemical resistance, making them attractive for aggressive CIP cycles; elastomers like EPDM are commonly used where strong alkaline cleaning occurs but have limited hydrocarbon resistance.

Regulatory and hygienic compliance

Food and pharma applications commonly require materials that meet FDA food-contact criteria (see CFR Title 21 - Food and Drugs) and, for pharmaceutical contact, USP biological reactivity testing (e.g., USP <88> or USP Class VI guidance) or specific extractables/leachables testing. Select materials with available certificates of compliance (CoC), material traceability records, and test data for extractables and cytotoxicity where applicable.

Material selection strategy

Start with the process chemistry (product to be sealed), operating temperature and pressure, cleaning agents (CIP/SIP chemicals and temperatures), and contact duration. Map these inputs to a short list of candidate materials, then review vendor test data, regulatory documentation, and historic field performance. For critical pharma contact points, plan for supplier-provided extractables/leachables (E&L) reports and compatibility test protocols that mirror your CIP/SIP parameters.

Design factors, installation and maintenance for food & pharma

Design geometry and surface finish

Wiper ring performance depends on groove design, shaft/rod surface finish, and tolerance. Typical recommendations: surface roughness Ra ≤0.4 µm on rod surfaces in hygienic applications, correct groove depth to maintain contact pressure without excessive friction, and chamfers to prevent seal damage on installation. Incorrect geometry can cause extrusion, accelerated wear, and particle generation—unacceptable in sterile production lines.

Installation best practices

Use proper installation tools (expanders, protectors) and procedures to avoid nicking or stretching seals. Where possible, install wiper rings after final inspection of shafts to minimize contamination entrapment. Provide documentation of installation torque, process conditions, and operator steps for GMP records in pharmaceutical settings.

CIP/SIP resilience and validation

Design the wiper selection around the most aggressive cleaning step expected (e.g., caustic hot CIP, steam-in-place at 121°C). Materials and construction must maintain dimensional stability under those conditions. Validation should include accelerated aging tests and full-cycle CIP/SIP exposure with subsequent functional testing to demonstrate continued sealing and no unacceptable degradation or extractables increase.

Comparing wiper ring materials and choosing a supplier

Material comparison table

Sources: material datasheets from major seal makers and consolidated material guidance (see e.g., O-ring - Wikipedia) and regulatory frameworks like FDA Food Contact.

Supplier selection criteria

When choosing a supplier for wiper rings, verify: manufacturing capability (cleanroom or dedicated hygienic lines for pharma), material traceability, testing equipment (FTIR, GC-MS for extractables, mechanical testers), documented quality systems (ISO 9001, ideally ISO 13485 for medical/pharma-related components), and long-term R&D relationships with universities or institutes. Request pilot batches and performance data under your process conditions.

Why documentation and testing matter

Procurement often focuses on unit price, but for food and pharma the hidden costs of failure (product recall, downtime, regulatory remediation) far exceed initial savings. Ask for Certificates of Conformity, full batch traceability, E&L reports for pharma contact, and accelerated aging/CIP test reports to make a defensible selection.

Polypac: capabilities and why it matters for food & pharma wiper rings

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. Polypac's custom rubber ring and O-ring factory covers an area of more than 10,000 square meters, with a factory space of 8,000 square meters. Our production and testing equipment are among the most advanced in the industry. As one of the largest companies in China dedicated to the production and development of seals, we maintain long-term communication and cooperation with numerous universities and research institutions both domestically and internationally.

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, we have expanded our product line to include O-rings made from various materials such as NBR, FKM, silicone, EPDM, and FFKM.

Polypac advantages and main products: Polypac combines material R&D with large-scale precision manufacturing to deliver hygienic-grade seals. Main product categories include O-Rings, Rod Seals, Piston Seals, End Face Spring Seals, Scraper Seals (wiper rings), Rotary Seals, Back-up Rings, and Dust Rings. Key differentiators: deep PTFE-formulation expertise (beneficial for aggressive CIP environments), extensive testing capabilities, and collaborative R&D ties with academic partners that accelerate material qualification for food and pharma use-cases.

For buyers, this means access to customized wiper ring designs (geometry and compound), documented traceability, and the ability to obtain pilot batches with test reports replicating your CIP/SIP cycles. When selecting a supplier, consider not just the seal geometry, but the vendor's ability to provide E&L data, long-term production stability, and rapid iteration on material formulations.

Testing, validation and lifecycle management

Recommended test matrix before release

For each wiper ring design, request or perform: dimensional inspection, hardness and tensile testing, accelerated aging (thermal and chemical), abrasion/wear testing under realistic stroke conditions, extractables/leachables screening for pharma contact, and functional CIP/SIP cycling. Maintain a traceable lot history for each installed part for future root-cause analysis.

Monitoring in service

Establish maintenance intervals based on operating hours and CIP cycles rather than fixed calendar replacement alone. Implement in-service inspection criteria (leakage thresholds, visual inspections for cracking or deformation, and particle monitoring downstream where feasible). Use condition-based replacement when operating data justifies it.

Case study summary (anonymized)

A mid-size dairy processor replaced a generic rubber wiper with a filled-PTFE scraper on a high-speed piston filler that experienced frequent downtime from seal wear. After compatibility testing with their CIP cycle (0.5% caustic at 65°C), the PTFE-based wiper reduced wear-related stops by 70% and extended primary rod seal life by 40%, demonstrating the value of matching material to cleaning chemistry and mechanical conditions. This emphasizes performing application-specific validation rather than relying solely on generic charts.

FAQs

1. What is the difference between a wiper ring and a scraper seal?

There is no practical difference—wiper ring and scraper seal are commonly used interchangeably. Both refer to an external seal intended to remove contaminants from a rod or shaft surface before they reach internal seals.

2. Which materials are best for repeated CIP/SIP cycles?

PTFE and filled PTFE grades typically offer the best resistance to aggressive CIP/SIP chemistries and high temperatures. EPDM is also commonly used where hot alkaline/steam cleaning is dominant. For critical pharmaceutical contact areas, FFKM may be used despite higher cost due to its exceptional chemical stability.

3. Do wiper rings need regulatory certificates like O-rings?

Yes. For food or pharma contact, suppliers should provide Certificates of Conformity, material declarations aligned with FDA or EU food-contact rules, and, for pharma, extractables/leachables data or USP Class testing as required by your QA protocols.

4. How often should wiper rings be replaced?

Replacement intervals depend on stroke frequency, CIP/SIP aggressiveness, and mechanical loading. Implement condition-based maintenance informed by periodic inspections and operational data; many operations find interval-based replacement combined with condition checks most reliable.

5. Can I use standard industrial-grade wiper rings in pharmaceutical equipment?

Not without verification. Standard industrial materials may lack the required material documentation, E&L data, or production controls (cleaning, contamination avoidance) needed in pharma environments. Always use materials and suppliers qualified for pharmaceutical use.

6. What documents should I request from a supplier?

Request manufacturing traceability, material safety data sheets (MSDS), certificate of conformity (CoC), hardness and dimensional test reports, extractables/leachables data (if pharma), and results from accelerated aging/CIP tests that simulate your process.

Contact & next steps

If you need tailored wiper ring solutions for food or pharmaceutical applications, Polypac offers custom material development, filled PTFE expertise, and comprehensive testing to validate performance in CIP/SIP environments. Contact Polypac's technical team to discuss material selection, prototype runs, or to request traceable documentation and test reports. View product options and request a quotation: contact@polypac.com (or visit supplier product pages for O-Rings, Rod Seals, Piston Seals, End Face Spring Seals, Scraper Seals, Rotary Seals, Back-up Rings, Dust Ring).

References and further reading: FDA - Packaging & Food Contact Substances (https://www.fda.gov/food/packaging-food-contact-substances-fcs); Hydraulic cylinder overview (https://en.wikipedia.org/wiki/Hydraulic_cylinder); O-ring standards summary (https://en.wikipedia.org/wiki/O-ring).