Diaphragm Valves for Pulp & Paper Industry
Knife gate valves, diaphragm valves, ball valves (CS/SS), and pinch valves for kraft pulping, black liquor handling, bleaching chemical circuits, and paper machine wet-end service.
Which diaphragm valves are used for pulp & paper industry?
Pulp and paper mills handle one of the most chemically diverse and mechanically demanding process fluids in industry: wood pulp suspensions at 3–14% consistency, black liquor (a highly caustic, high-solids alkaline solution at elevated temperature), white liquor (NaOH + Na₂S), bleaching chemicals (ClO₂, H₂O₂, NaOH, SO₂), and paper machine white water with fine fibres and fillers. Valve selection must account for abrasion from fibres, chemical attack from strong alkalis and bleaching agents, and the stringent availability requirements of a continuous paper machine.
Diaphragm Valve (Chemical / Bleach Plant)
Zero leakage for bleaching chemicals (ClO₂, H₂O₂, NaOH) - no packing in contact with aggressive bleaching agents
Critical Requirements
- Abrasion resistance for pulp fibres - natural rubber or EPDM liners with hardness 60–70 Shore A for knife gate seats
- Full-bore, self-draining design for pulp stock - prevents fibre plug formation when valve is closed
- Chemical resistance to bleaching agents: ClO₂, H₂O₂, NaOH, SO₂ - PTFE or PVDF diaphragms for oxidising bleach chemicals
- High-temperature capability for black liquor (up to 150°C) - SS 316 or alloy steel body; A217 WC6 for recovery boiler steam
- IBR certification for valves on recovery boiler steam lines (high-pressure steam service)
- Replaceable wear components (sleeves, liners, diaphragms) - essential for minimising mill downtime
Service Challenges
- Black liquor (pH 12–13, sodium carbonate, sodium sulphide, solids up to 65%) at 90–150°C - highly alkaline, scaling; SS 316 minimum
- White liquor (NaOH + Na₂S, pH 13–14) - strongest alkali in process; SS 316L or duplex for valves on white liquor lines
- Pulp stock (fibrous suspension, 3–14% consistency) - abrasive, plugging in dead legs; knife gate or pinch valve preferred
- ClO₂ (chlorine dioxide bleaching stage) - powerful oxidiser; PTFE-lined diaphragm valves or PVDF-bodied valves only
- H₂O₂ (peroxide bleaching) - oxidising; PTFE or PVDF wetted components, avoid carbon steel
Vajra Diaphragm Valves
Elastomer-lined valves for corrosive, abrasive, and sterile applications.
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