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Packing: Braided Flexible Graphite Replaces Filament Yarn

Waterous has changed the packing material used in our centrifugal fire pump product line from filament yarn graphite packing to braided flexible graphite (BFG), effective August 2002. This change was made after extensive testing of various packing materials over a two-year period upon learning that filament yarn graphite packing material would no longer be available from the manufacturer.

Waterous pump users should be aware of certain differences in the performance of the BFG packing material. The differences are highlighted below:

Temperature of packing gland and stuffing box area: BFG packing is designed to transmit heat away from the impeller shaft, and the result is the packing gland and stuffing box area may heat up. During initial run-in of the packing, temperatures up to 300°F (150°C) may be experienced with steam or bubbling of flush water coming in contact with the heated packing gland.

Packing adjustment and leakage rate: Desired leakage rate is 10 to 120 drops per minute through the packing, although we have determined through testing that leakage may diminish and/or start at zero leakage and may not respond to loosening of the packing nuts to restore or develop leakage. Any necessary packing adjustments should be accomplished with 1/2 to 1 flat increments to the packing nuts. Each adjustment should be allowed to run in for 10 to 15 minutes between adjustments.

Indications that packing needs to be replaced: Packing gland and stuffing box temperatures in excess of 300°F (150°C) or excessive leakage that does not respond to adjustment.

Material: We no longer combine filament yarn graphite packing and flexible graphite packing in the stuffing box, we now use straight braided flexible graphite (BFG) packing in the stuffing box.

Details

The difference in the performance of the new BFG packing material and the filament yarn graphite are due mainly to differences in heat transfer capability and temperature limitations. With traditional packing such as the filament yarn graphite, flush water is required to cool and transfer the frictional heat created between the rotating impeller shaft and the packing ID. Maintaining an observed drip rate from the stuffing box during pump operation ensures this cooling. If this frictional heat is not dissipated, the packing will fail, and the heat that is generated will, most likely, ruin the impeller shaft.

The BFG packing dissipates the frictional heat generated between the impeller shaft O.D. and the packing I.D. Its natural characteristic is to transfer the heat through the cross-section of the packing to the next closest material (the stuffing box and packing gland). This will cause the packing gland and the stuffing box (pump body) to heat up, in some cases to the point that it is very hot to the touch. This is desirable. The damaging heat transfers away from the rotating impeller shaft and into the housing of the pump body. Steam or bubbling of the flush water coming in contact with the heated packing gland may be seen. The packing gland and stuffing box and pump body may reach temperatures up to 300°F (150°C), but should not exceed 300°F (150°C).

If you have any questions regarding this information or need any assistance, please contact us at: 
Telephone: 651-450-5200
Fax: 800-488-1228
service@waterousco.com

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