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Caustic Soda (NaOH) Dosing Pump: Viscosity, Metallurgy & Seal Selection
Caustic soda (Sodium Hydroxide, NaOH) at 48% to 50% commercial concentration exhibits high viscosity (up to 100 cP at room temperature) and tends to crystallize when cooled below 15°C. For industrial neutralization and process dosing, heavy-duty SS 316 or PTFE plunger and diaphragm metering pumps with heated heads or oversized check valves ensure continuous, reliable dosing.
Corrosion & Dosing Dynamics: Caustic Soda (NaOH)
While caustic soda is an alkaline base rather than an acid, warm concentrated solutions attack ordinary aluminum, zinc, brass, and carbon steel. Furthermore, high-temperature caustic (>65°C) induces caustic embrittlement and stress corrosion cracking in unstabilized stainless steels. Cold 48% caustic soda becomes extremely thick and prone to salt crystallization on valve seats and gland packings, requiring heavy-duty spring-assisted check valves.
Recommended Engineering Specifications for Caustic Soda (NaOH)
| Parameter | JEW Factory Recommendation |
|---|---|
| Recommended Pump Type | Reciprocating Plunger Pump (GDP Series) or Mechanical Diaphragm Pump |
| Liquid End Metallurgy | SS 316 / SS 316L / Carbon Steel (Heavy Wall) / Pure PTFE |
| Plunger Rod Material | Hard Chrome Plated SS 316 / Solid Alumina Ceramic (abrasion resistant) |
| Check Valve Assembly | Spring-loaded SS 316 / PTFE Balls with generous flow orifices for viscous liquid |
| Gland Packing Style | PTFE Impregnated Braided Packing with adjustable lantern ring gland |
| Viscosity Capacity | Capable of handling up to 1000 cP with reduced stroking speed |
| Motor Power | 0.5 HP to 3.0 HP High-Torque TEFC Electric Motor |
| Calibration Standard | API 675 linear stroke output (0 to 100%) with ±1% repeatability |
Piping, Priming & Installation Best Practices
- Heat Tracing for Cold Environments: If operating in winter or outdoor plants where ambient temperatures dip below 15°C, install heat tracing and insulation on caustic lines to prevent crystallization.
- Oversized Suction Piping: Due to the viscosity of 48% NaOH, size suction pipe diameter one nominal size larger than the pump connection to minimize friction head loss.
- Flush Line at Shutdown: If the pump will remain idle for more than 48 hours, flush the head with warm demineralized water to prevent caustic crystals from locking check valve balls.
- Water Washing of Gland Packing: For plunger pumps, connect a low-pressure water flush to the lantern ring to continuously dissolve any caustic crystallization at the packing face.
Frequently Asked Engineering Questions
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Jagdish Engineering Works manufactures custom chemical dosing pumps and turnkey skids with 55+ years heritage. Delivered with Mill Test Certificates & Hydrostatic Test Logs.
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Jagdish Engineering Works, Mumbai – manufacturer of plunger and diaphragm metering pumps and pressure relief valves since 1969. Our engineers design, test and repair dosing pumps for water treatment, chemical, refinery, fertilizer, sugar and paper plants.
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