Pulp & Paper: Mechanical Seal Solutions for Stock, Liquor & Agitators

Paper mills run hard—abrasive fibers, fillers, high-pH liquors, frequent wash-ups, and hot condensate all stress conventional seals. The right mechanical seal design, materials, and support plan keep pumps and mixers leak-free, reduce dilution, and cut maintenance downtime.

Where seals are used in pulp & paper

• Stock & fan pumps (approach flow, machine chest, headbox feed)
• Medium- to high-consistency stock pumps and refiners
• Bleach plant & chemical dosing (chlorine dioxide, peroxide, caustic)
• White/green/black liquor circuits & recausticizing
• Washers, screens, thickeners and agitators
• Hot condensate / vacuum pumps around the dryer section

Typical sealing challenges

• Abrasive slurry: fibers, sand, kaolin, and fillers wear faces and springs
• High alkalinity & oxidizers: white/green/black liquor, ClO₂, H₂O₂, NaOH
• Dilution control: many positions must avoid flush water
• Air entrainment & dry-run during wash-ups and start/stop
• Shaft movement on large vertical and cantilever pumps
• Build-up (“stickies”) causing clogging around springs

Recommended sealing strategies

1) Stock & fan pumps (low to medium consistency)

• Design: Single balanced pusher seal; protected or non-clog springs
• Faces: Carbon vs. SiC for economy; SiC vs. SiC for longer life
• Flush: Plan 11/13 recirculation; add cyclone separator if grit is present
• Elastomers: EPDM in alkaline water, FKM if oils/solvents appear

Sakowitz fit: practical single seals such as MG1/MG12, Type 2/Type 82, 2100; plug-and-play cartridge versions available.

2) Medium-/high-consistency stock & abrasive duties

• Goal: No dilution and high reliability under poor lubrication
• Design: Double pressurized cartridge (Plan 53) with pumping ring
• Faces: Hard-hard (SiC/SiC or TC/TC) for abrasion
• Barrier fluid: Water-glycol or light oil, 1.5–2.0 bar above box pressure

Sakowitz fit: heavy-duty double cartridge assemblies (Cartex-DN class), custom sleeves/glands to match installed pumps.

3) Liquor circuits (white/green/black)

• Chemistry: high pH, sulfides, carbonate—corrosion risk
• Metals: 316L standard; Duplex 2205 where chloride stress is expected
• Elastomers: EPDM for alkaline water; PTFE in strong oxidizers (bleach)
• Design: Single balanced with Plan 32 clean flush or double when dilution must be zero

Sakowitz fit: double cartridge seals for liquor pumps; single balanced cartridge with PTFE/EPDM secondary seals for bleach plant service.

4) Agitators, washers, thickeners

• Design: Double seals with pressurized barrier and quench (Plan 62) to prevent crusting
• Options: Tapered faces & robust bearings to handle shaft deflection

Sakowitz fit: engineered double cartridge packages with integrated flush ports and quench features.

5) Hot condensate / vacuum pumps (dryer section)

• Design: Metal bellows seals (elastomer-free) to resist blistering
• Faces: Carbon/SiC or SiC/SiC with low heat generation
• Notes: Ensure proper venting and pre-lube to avoid dry start

Sakowitz fit: metal bellows series (M21/MFL) and compact cartridge versions for quick retrofit.

Materials selection guide

• Faces:
  • Carbon/SiC – value choice for clean stock or condensate
  • SiC/SiC – best all-rounder; handles abrasives and upset conditions
  • TC/TC – extreme abrasion on high-consistency or sandy stock
• Metals: 304/316 standard; Duplex 2205 for chloride/erosion; special alloys on request
• Elastomers: EPDM (alkaline water), FKM/Viton® (oils/solvents), PTFE (strong oxidizers)

Reliability tips for mills

• Set gland flush and barrier flows/pressures and log them on start-up
• Use particle separators/strainers to protect faces in gritty services
• Avoid dry-start: vent chambers and prime pumps after wash-ups
• For double seals, maintain barrier fluid 1.5–2.0 bar above box pressure

Why mills choose Sakowitz

• Application-driven engineering for stock, liquor and agitator positions
• Fast OEM cross-reference from pump model or old-seal dimensions
• Cartridge designs that cut install time and reduce start-up leaks
• Short lead times with stocked SiC/TC faces, 316/duplex metals, EPDM/FKM/PTFE

Featured products for Pulp & Paper

• Double Cartridge Seals – pressurized systems for medium/high-consistency stock, liquor pumps, and agitators (Cartex-DN class).
• Metal Bellows Seals – M21/MFL – ideal for hot condensate and elastomer-sensitive duties.
• General-Purpose Singles – MG1/MG12, Type 2/Type 82, 2100 – reliable choices for clean stock and utility water.
• Heavy-Duty Slurry Options – 318-type for fibrous/abrasive slurries where a robust single or double configuration is needed.

Need a one-to-one replacement? Send shaft size, box bore/length, pump model, and photos—we’ll match or upgrade with a Sakowitz solution.

FAQ

Q1: How can we avoid product dilution around the headbox?
 Use a double pressurized cartridge with a self-contained barrier system (Plan 53). It seals without adding flush water to the process.

Q2: What elastomer works best with white/green/black liquor?
 Typically EPDM for alkaline liquor. For bleach plant oxidizers, upgrade to PTFE.

Q3: When should we choose metal bellows?
 For hot condensate or services where elastomer blistering or shrinkage is an issue.

Q4: Can you adapt to our existing pump glands?
 Yes. We supply complete cartridge kits (gland, sleeve, hardware) and custom drillings/ports to fit your pump.