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Large Diameter Seals For Many Applications

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Edited by: Andrew Long
Last Updated: 15th April 2011

FTL Technology supplies to order, bespoke high-performance seals for larger applications. These can be as OEM in association with plant manufacturers or as replacements to industrial customers. So far, the largest supplied has been 2,880mm (9' 5") diameter PTFE vacuum ring seal. 

To design these large seals, we need a great deal of specific information on its geometry and performance requirements including:

- Chemical composition of the media to which the seal may come into contact

- Operating parameters such as operating pressures & temperature ranges either side of the seal and vibration characteristics

- Maintenance requirements - e.g. need to open/break the seal - target seal life in service

- Geometry and tolerances for the mating parts including coefficients of expansion requirements (a significant factor for large plant seals)

- Risk analysis for the consequences of a seal failing - i.e. its security requirements.

FTL Technology's experts take this information and seek the most appropriate specialist seal manufacturer to meet the plant's needs. For large plant seals, FTL works with ElringKlinger who manufactures PTFE seals.  Currently, they have the capacity to make seals up to 2,880 mm (9' 5") diameter from a choice of more than 600 compounds.

Individual designs of seal require a number of manufacturing steps in the process and this can take several days for each seal.  The sintered blank once cooled, then machined to the required profile and to the design tolerances.  The final geometry and characteristics can range from a simple ‘O' ring, spring-loaded U/V ring to labyrinthine profile seals.

As an example, FTL commissioned ElringKlinger to manufacture a 1,150mm (45") diameter spring-loaded PTFE ‘U' ring vacuum seal for a double-motion agitator that rotated at a rim speed of 2.5m/s.  Also, it was for a service life of 2,000hrs.  Large seals like this need careful handling, support and packaging to avoid over-stressing it during storage, carriage from factory to the customer's plant, and locating it in the machine's groove.  

Large PTFE parts are not only supplied as seals but as structural parts for large plant machinery and pipelines.  The material's excellent non-stick properties, chemical resistance and high thermal stability make PTFE an excellent choice. 

Common applications are movement joints (bellows) between to parts of a machine or pipeline connections to machines used in the chemical industry that need to withstand temperatures up to 200°C, be resistant to aggressive chemicals and the surface must have non-stick properties to avoid scaling.  The PTFE construction admirably fits the bill.

Rectangular and irregular shaped PTFE constructions are also available.  One such application is the interleaved spacers for plate heat exchangers which then ensures longer maintenance intervals between dismantlings.