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Pump seal selection considerations

04 January 2021

Paul Green explains how seals and support systems on food industry pumps can help food industry engineers meet many of their daily challenges as well as helping to meet sustainability goals. 

Food processing pumps are crucial to maintaining the uninterrupted operations on which a healthy profit margin relies so it makes sense that every component contributes to the overall reliability of the pump – and that includes the seals.

Industry specific pump seals can contribute significantly to minimising leakages, helping reduce product loss or contamination, and minimising unscheduled downtimes. 

Mechanical seal support systems can also bring the added benefits of reducing water wastage to virtually nil, cutting energy costs and improving reliability.

Ensure traceability
It should be remembered that pump seal components will often have incidental contact with food and are therefore subject to Regulation EC1935/2004 on materials and articles intended to come into contact with food (FCM Regulation) and Regulation EC2023/2006 on good manufacturing practices (GMP) for materials and articles intended to come into contact with food.

It is therefore important to source pump seals which come with certified material traceability. Always look at the label and if a mechanical seal comes in packaging that doesn’t clearly state its compliance, then do not use it!

Daily high pressure wash-downs present an ongoing risk to bearing life. Almost 50% of bearings failures are the result of contamination of the lubrication oil, by water ingress as well as process fluid or particles of dust and dirt.

Research indicates that water contamination as low as 0.002% – that’s 20 parts per million or just a single drop of water in a typical bearings chamber – can reduce bearing life in some oils by as much as 48%. 

The most advanced labyrinth bearing protection incorporates dynamic lift technology to facilitate the ‘breathing cycle’ required to ensure a healthy environment for bearings and ensure optimum efficiency, while preventing the ingress of contaminating dust and moisture. 

This involves using the centrifugal force of rotating equipment to open a temporary micro gap, allowing expansion of the oil/air mixture in the bearing housing and enabling the equipment to ‘breathe’. When the equipment stops rotating the micro gap immediately closes, forming a perfect seal against potential contaminants and moisture ingress.

Unlike commonly used lip seals, which are designed to contact the shaft, advanced bearing isolation can also offer significant energy savings due to its non-contacting design. 

Improve sustainability
Seal reliability depends on maintaining a consistent fluid film at the inboard seal face. 

Commodity processing plants operate in water soluble slurries. Centrifuges and evaporators separate and refine the finished product. As the product thickens and becomes sticky, seal reliability becomes critical. 

Traditional piping plans – such as plan 53-A or plan 54 – are insufficient to this task, and cross-contamination and inconsistent pressure controls are common problems faced by food processors.

Under a traditional plan 53-A set-up, the tank has a fixed volume of liquid pressurised by nitrogen or compressed air. During process upsets, this tank empties and the seals run dry. This can result in costly unscheduled stoppages, which for food producers working to tight schedules, can have serious implications down the line.

This issue can be eliminated by selecting double mechanical seals with a seal support system. These water management systems use an integral vessel to supply clean, cool flush water to the seal faces. Wastage through quench to drain or evaporation at the end of a process is reduced to virtually nil, offering significant cost savings as well as improved reliability. 

With sustainable water management systems the mechanical seal is consistently supplied with a compatible fluid at a pressure higher than the product pressure, ensuring a stable and clean fluid film is maintained at the seal faces. Because seal support systems can be connected directly to the plant water line, which becomes the system’s fluid and pressure source, the mechanical seals are protected from harmful products, making them, and therefore the pump itself, more reliable. 

Concerns about the risk of contamination from bacteria growth in the recycled fluid can be allayed by selecting water vessels which are specifically designed to meet stringent hygiene standards demanded by the food industry. Unlike standard sealed vessels – where access to the interior of the vessel is extremely limited making clean-in-place processes almost impossible –  look for solutions which can be disassembled for easy inspection and cleaning. 

When selecting a sealing solution for food processing pumps it is worth taking the following into consideration:

• Correctly specifying mechanical seals and installing advanced bearing isolation at the initial project stage can support superior reliability, as well as ensuring compliance with industry regulations.  
• Standard mechanical seals and support systems can be retrofitted onto OEM equipment, making upgrades uncomplicated and extremely cost-efficient.
• The use of double mechanical seals and support systems can significantly improve equipment reliability, dramatically enhancing production uptime and reducing plant downtime.
• Water usage reductions can also be made by the use of water management systems, removing the costs associated with ‘water to drain’ systems and the associated effluent management costs.
• Investment in non-contacting bearing isolation can dramatically reduce energy costs as well as supporting superior pump reliability. 
• A simple and effective hygiene solution can support industry specific requirements, ensuring regulatory compliance.
Remember, the question ‘how much will it cost’ should always be considered alongside ‘what return on investment does it offer’?

Paul Green is UK sales manager at AESSEAL.

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