The Mechanical Seal

The mechanical seal assembly (Figs 7.14 and 7.15) is now commonly used in both small and large fermenters. The seal is composed of two parts, one part is stationary in the bearing housing, the other rotates on the shaft, and the two components are pressed together by springs or expanding bellows. The two meeting surfaces have to be precision machined, the moving surface normally consists of a carbon-faced unit while the stationary unit is of stellite-faced stainless steel. Steam condensate is used to lubricate and cool the seals during operation and serve as a containment

Stirrer Gland Bearing Fermenter

Fig. 7.13. Packed-gland stirrer seal (Chain et a/., 1954) (Components: 1, agitator shaft; 2, stuffing box; 3, upper cap; 4, lock ring; 5, lower cap; 6, chuck; 7, greasecup; 8, lock ring; 9, lock nut; 10, distance ring; 11, half coupling; 12, half coupling; 14a, washer; 14b, nut; 15, impeller; 16, shim; 17, packing rings).

Fig. 7.13. Packed-gland stirrer seal (Chain et a/., 1954) (Components: 1, agitator shaft; 2, stuffing box; 3, upper cap; 4, lock ring; 5, lower cap; 6, chuck; 7, greasecup; 8, lock ring; 9, lock nut; 10, distance ring; 11, half coupling; 12, half coupling; 14a, washer; 14b, nut; 15, impeller; 16, shim; 17, packing rings).

barrier. Single mechanical seals are used with a steam barrier in fermenters for primary containment at level 1 or B2 (Werner, 1992), whereas double mechanical seals are typically used in vessels with the outer seal as a backup for the inner seal for primary containment at level 2 or B3 (Werner, 1992; Leaver and Hambleton, 1992; Fig. 7.15). At level 2 or B3 the condensate is piped to a kill tank. Monitoring of the steam condensate flowing out of the seal is an effective way for checking for seal failure. Disinfectants are alternatives for flushing the seals (Werner, 1992).

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