A mechanical seal in pharmaceutical service has to keep its wetted parts from altering the product, through every cleaning and steam-sterilizing cycle the plant runs on it. In practice that means a hygienic design, and faces and elastomers chosen for steam and cleaning chemicals. It also has to arrive with the documents the plant needs to verify its materials.

Which Regulations Apply to a Pharmaceutical Mechanical Seal

The regulations that apply to a pharmaceutical mechanical seal are the US CGMP rules in 21 CFR 210 and 211 and EU GMP, through their clauses on production equipment. No regulation covers the seal as a product; these rules regulate the drug maker, and the US clauses that reach the seal are:

  • 21 CFR 211.65(a): surfaces that contact the product must not be “reactive, additive, or absorptive” so as to alter the drug product. This clause covers a seal’s wetted materials.
  • 21 CFR 211.63: equipment must be designed for its intended use and for its cleaning and maintenance.
  • 21 CFR 211.67: equipment must be cleaned, maintained and, where the drug requires it, sanitized or sterilized at appropriate intervals under written procedures.

EU GMP Chapter 3, clause 3.39, sets the 211.65(a) requirement in nearly the same words.

ASME BPE, a voluntary consensus standard for bioprocessing and pharmaceutical equipment, addresses mechanical seals directly. Its sealing-components part is Part MC in the 2024 and 2026 editions (older documents call it Part SG). ASME BPE-2026 was issued on 1 May 2026 and takes effect six months after that date, so name the edition the spec cites.

The work splits accordingly. The seal supplier qualifies and certifies its materials, biocompatibility testing included; the plant specifies the seal, verifies the materials at installation and keeps the cleaning and maintenance records.

FDA Material Compliance

For a seal’s elastomers and plastics, “FDA compliant” means the compound meets a food-contact listing in 21 CFR 177, on its maker’s own determination. The usual sections are 177.2600 for rubber articles intended for repeated use and 177.1550 for perfluorocarbon resins, PTFE included.

Both sections are food-contact regulations, written for food. Treat an FDA statement as the minimum for wetted elastomers and plastics, and ask for the compound maker’s compliance statement or letter of guaranty naming the 177 section.

USP Class VI and the 2026 Revision

USP Class VI is one of six plastics classes defined in USP chapter <88>, and the revised <88> that becomes official on 1 December 2026 deletes the classification.

ASME BPE-2026 removes all Class VI references and asks for in vitro cytotoxicity testing only, per USP <87> or ISO 10993-5.

For a replacement seal, Class VI documents already on file may stay usable, because ASME BPE can accept applicable past in vivo results as biocompatibility evidence. For new compounds, ask for <87> cytotoxicity or ISO 10993-5 results.

EU Rules for Seal Materials

The EU rule that binds a pharmaceutical plant is EU GMP Chapter 3, clause 3.39, which requires that product-contact parts not affect product quality and leaves the choice of material to the manufacturer.

Seal suppliers usually cite EU food rules:

  • Regulation (EC) No 1935/2004: covers materials and articles intended to contact food, and requires a written declaration of compliance where specific measures apply.
  • BfR Recommendation XXI: German recommendations for natural and synthetic rubber in contact with food.
  • EHEDG Guideline 25: design of mechanical seals for hygienic and aseptic food applications.

Hygienic Design

A pharmaceutical seal has to be cleanable and drainable in place: no crevice, shelf or dead leg that CIP fluid or steam cannot reach and drain from, and wetted metal polished well beyond a standard machined finish. The features to check on the drawing:

  • O-ring grooves: grooves, threads and metal-to-metal joints form crevices, so hygienic seals enlarge the groove clearances to let CIP fluid and steam reach the elastomer, and isolate internal threads with static O-rings or replace them with hygienic fittings.
  • Drainability: continuous sloped surfaces, with no flat area that pools liquid.
  • Dead legs: no area without circulation or drainage, including flush ports; a gland port used for cleaning is angled so it drains.
  • Surface finish: wetted metal is electropolished or mechanically polished.

For pumps in WFI service, wetted surface roughness is held below 0.5 µm Ra. ASME BPE sets acceptance criteria for process-contact surface finishes in its Part SF; write the finish grade for the seal’s wetted metal into the purchase spec.

Withstanding CIP and SIP

A pharmaceutical seal has to survive repeated saturated-steam sterilization and hot chemical cleaning without leaking, losing elastomer properties or trapping residue.

Steam sterilization is referenced to 121 °C for at least 15 minutes in the European Pharmacopoeia. The plant’s own SIP temperature and hold time are the figures to put on the seal spec.

CIP usually runs once per batch, with caustic and/or bleach solutions at elevated temperature. In a dual seal with an oil barrier, the barrier oil is heated above 110 °C (230 °F) to sterilize the seal cavity.

ASME BPE carries a nonmandatory appendix of standard process test conditions that simulate SIP and CIP cycles, with leakage, intrusion into the flow path and condition after exposure as the criteria. Ask the supplier whether the seal design has been tested to it.

Seal Materials

Wetted metal parts of a pharmaceutical seal are 316L stainless steel or a higher alloy such as AL6XN or 2205. The other seal material choices are the faces and the elastomers.

Seal Face Materials

Silicon carbide is the face material for WFI and other hot purified water, run against a second hard face wherever carbon dust must not reach the product.

Hard-against-hard face combinations need a liquid film or low speed and cannot run dry, so they are usually run inside a dual seal with a barrier fluid.

Some suppliers offer tungsten carbide. In a liquid, its metallic binder, cobalt in the common grade, is the phase that corrodes and releases binder metal into the fluid. If tungsten carbide is offered, ask which binder it uses.

Elastomers

Between EPDM and FKM, EPDM is the default for water and steam, and FKM belongs in steam service only in a peroxide-cured grade. FFKM is for duties with both steam and aggressive chemicals, where its cost is justified. EPDM’s weakness is chemical resistance, and both EPDM and HNBR lose their resistance above 150 °C.

Standard FKM is bisphenol-cured and fails early in hot water and steam. Peroxide-cured FKM grades resist steam, and newer compounding lets FKM withstand steam-cleaning regimes up to 200 °C.

A compliance label does not make two compounds equal. Specify the compound by maker and compound number, and hold the supplier to it.

Single or Double Seal

A pharmaceutical application needs a double mechanical seal when any of these apply:

  • Vacuum or sterile boundary: the outboard seal keeps air and atmospheric contaminants out of the process.
  • Particle-free product: the barrier lubricates hard-face pairs, so no carbon face sheds dust into the batch.
  • Containment on failure: if the inboard seal fails, the outboard seal holds the process and the repair can be planned.

ASME BPE draws pressurized and unpressurized dual seals for pumps and pressurized dual seals for top-entry agitators, with numbered seal support plans, so the same terms work in a pharmaceutical spec. The barrier or buffer fluid has to be compatible with the product, such as purified water, mineral oil or glycerin.

Seals by Equipment

The equipment changes the seal arrangement, while the regulations and materials above apply to every seal.

Process Pumps

A seal on a pharmaceutical process pump has to drain with the pump for SIP, and in hot purified water it is best served by a double seal with silicon carbide faces. The seal chamber and gland must have no pocket that holds condensate after SIP.

Reactors, Mixers and Dryers

A seal on a pharmaceutical reactor, mixer or dryer shaft has to keep carbon wear dust out of the batch and keep air out under vacuum, often on a vertical shaft where the seal runs dry.

Three arrangements meet those two needs:

  • Debris well: a labyrinth, also called a sanitary gland, mounted between the seal and the vessel catches the carbon dust; it needs clean-out ports for CIP or SIP and must drain.
  • Liquid dual seal: the barrier lubricates hard faces and the outboard seal keeps air out under vacuum, at the cost of a barrier fluid that has to be heated for sterilization.
  • Gas-lubricated seal: contacting or non-contacting faces run on sterilized gas, with non-contacting faces lifting off to cut wear further; it removes the hot barrier fluid but needs a more complicated seal and support system.

Documentation and Traceability

A pharmaceutical seal should arrive with documents that let the plant verify every wetted material and trace it to its source:

  • Certificate of conformance: for polymer and other non-metallic parts; ASME BPE specifies the content it must carry.
  • Biocompatibility evidence: USP <87> cytotoxicity or ISO 10993-5 results for the wetted elastomers and plastics, or historical USP Class VI results for legacy parts.
  • FDA compliance statement: the compound maker’s statement or letter of guaranty naming the 21 CFR 177 section.
  • Metal inspection certificates: for wetted metal parts; EN 10204 type 3.1 is the certificate commonly requested.

The seal should also come with the supplier’s operating and maintenance instructions, which the plant’s installation qualification collects under EU GMP Annex 15.

A replacement seal should be built from the same compound, and the supplier should tell the plant before it changes the compound or its manufacturing process.