Rotary shaft seals for Pulp & Paper.
Pulp and paper mills run large shafts in punishing chemistry: caustic black liquor, hot white water, lime mud, hydrosulfide. The seal challenge is shaft size as much as chemistry — many pulp digester agitators use shafts six inches in diameter or more, often trapped between bearings that won't come off without a planned outage.
01The challenge
Why sealing this service is hard.
These are the failure modes our application engineers have catalogued from twenty-five years of pulp & paper installations. Most are visible only after a seal has been pulled.
- 01
Large shafts that can't be pulled
Pulp digester agitator shafts are commonly 4 to 8 inches diameter, welded into top-entry housings, and can't be removed without a turnaround. Split seals are the only practical answer.
- 02
Black liquor at 180 °F continuous
Hot black liquor is alkaline (pH 13+), high-solids, and crystallizes on cool surfaces. Standard seals foul in weeks. Outside-mounted designs (7600) keep the running gear out of the liquor.
- 03
White water with high grit content
Recirculated white water carries enough fiber and filler to act as a mild abrasive. Tungsten faces or silicon-carbide faces last several times longer than standard ceramic.
- 04
Lime mud and recovery cycle
Lime mud at the recovery boiler is hot, alkaline, and abrasive — the worst seal service in the mill. The 9700-WC is the standard recommendation for this duty.
02Recommended series
What we ship for pulp & paper.
9700 Series
When the process is mean — strong acids, hot brine, abrasive slurries.
View specsSeriesSPLITSplit Seal
Install without pulling bearings — for the shaft you can't dismantle.
View specsSeries76007600 Series
Outside-mounted single mechanical seal for thin liquids and mild corrosives.
View specsSeriesAST60AST60
Drop-in cartridge seal for ANSI B73.1 chemical process pumps.
View specs03Common equipment
Where we typically install in pulp & paper plants.
04Compliance & materials
Documentation we ship with the seal.
- Custom split housings up to 14-inch shaft for trapped digester drives
- EPDM secondaries rated for caustic black liquor at 200 °F continuous
- API plan 13 / 52 / 53A flush configurations on AST60 cartridge seal
- Pressure-rated to 50 psig with hydrostatic test certificate
05Engineering FAQ
What plant engineers ask before specifying.
Pulp & Paper · sized in 24 hours
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