Doubling up: How dual mechanical seals can protect sensitive pharmaceutical processes

For a successful pharmaceutical business, contamination control is non-negotiable in every process. Microscopic contamination in rotating equipment can compromise product batches and affect production schedules.  

And there is a lot of technology under pressure. While pumps, mixers, vessels and agitators are major sources of contamination and emissions, mechanical seals are the first line of defence in bioprocessing, managing sterile production, solvent handling and high-purity formulations. 

Dry-running vessel, mixer and agitator seals, often in single or dual configurations, strengthen that defence and play a uniquely critical role in preventing contamination during agitation, heating, cooling, Clean-in-Place (CIP) and Sterilise-in-Place (SIP) cycles. 

The contamination challenges 

Pharmaceutical processes are equipment-led, with every element playing an equal role. Top-entry mixers, vessels and agitators all contribute to production success and are subject to scrupulous sterilisation processes. They create distinct issues for the process owner.  

Variable pressure environments 

Agitators and top-entry mixers are subject to pressure/vacuum cycling, foaming and splashing during CIP and SIP. These conditions can be intense – for example, SIP involves steam at up to 134 °C. For that reason, operators tend to mix wet seals and dry-running seals, depending on the equipment and operational function.  

Regulatory pressure for zero contamination 

Commercial pressure to maintain product integrity is one challenge, intrinsically linked to the regulatory compliance obligation. The Food and Drug Administration (FDA) and Good Manufacturing Practice (GMP) guidelines demand closed and sterile processes which create fully sealed, closed environments that eliminate human contact, reducing contamination risks and meet stringent FDA/GMP guidelines such as (EU Annex 1). Meanwhile, EHEDG guidelines outline the hygienic design considerations required for a risk-based approach to preventing product contamination. 

Barrier fluid ingress risks 

Barrier fluids can alter the chemical composition, pH or viscosity of the process, potentially inhibit chemical reactions or reduce product efficacy.  

Barrier fluid contamination concerns 

Wet lubricated seals risk barrier fluid ingress, and contamination of a high-purity product can ruin batches and affect the company’s ability to meet regulatory standards. 

Cleaning and sterilisation challenges 

Mechanical seals must withstand steam sterilisation, aggressive CIP chemicals and repeated thermal cycling without introducing particulates or wear debris.  

Dry mechanical seals: A step change in contamination prevention 

Dry mechanical seals use two flat faces, one stationary and one rotating, to create a barrier between two surfaces. The seal faces are in close contact with each other, creating a tight seal to prevent fluid or gas leakage, without using liquid barrier fluids that can reduce contamination. This offers several pharma-specific benefits: 

Supporting CIP and SIP: Dry/non-contacting mechanical seal technologies 

The Type 5280 is a hygienic agitator seal for steel vessels and is popular in ultra-clean pharmaceutical applications. It meets Qualified Hygienic Design (QHD) and GMP standards and guidelines to enable the cleaning and sterilisation of the product wetted process area with the seal in place (CIP, SIP).  

Modular in design, the Type 5280 is available in liquid-lubricated (Type 5280 W), gas-lubricated (Type 5280 G) and dry-running (Type 5280 D) versions as well as a unique gas/dry face combination (Type 5280 GD). This seal family includes the Type 5281 for glass-lined vessels and the Type 5282 for special alloy vessels. 

Similarly, the Type 32 dry-running agitator seal operates without external fluid lubrication, reducing contamination risks. Well-suited for water-sensitive or dilution-sensitive applications, it meets pharmaceutical processing standards, and the optional debris well facilitates easy flushing. 

Seal technology to support sterilisation and process demands 

Similarly, the CK series of vessel and agitator seals supports steel, glass-lined and alloy vessel designs. Exchanging the seal faces on the Type CK-725 vessel and mixer seal will convert from the liquid lubricated Type CK 725W to a contacting dry-running seal (Type CK 725D), and both offer particle-free performance during sterilisation.  

The Type CK-726 is designed for steel-made agitated chemical reaction vessels to DIN 28136, can switch between wet and dry operation, and offers debris well and cooling flange options. Meanwhile, the Type CK 728 is available in liquid-lubricated (W), gas-lubricated (G), dry-running (D) or a unique gas/dry face combination (GD) format. 

Our non-contacting gas seal technologies include metal bellows seals, including the Type 2874 HTC. It meets rigorous industry standards and requirements, offering another option for pharma processes. Flexible, corrugated metal components reliably seal fluids up to 425°C (800°F) using high-temperature, corrosion-resistant (HTC) metal bellows technology.  

Meanwhile, dry-running split seals, such as the Type 3740D, are often used on pumps and vessels, including mixers and agitators, in pharmaceutical setups and are suitable for use in equipment according to 2014/34/EU (ATEX 95) Group II, Category 2 GD. 

Pharmaceutical customers operate to particularly stringent sealing standards to protect product and environmental integrity. Having a tandem setup can offer that extra level of security. In the next part of our blog, we look at how dedicated seals, support systems and service agreements create an integrated sealing strategy to meet global standards.  

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