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Hydrochloric Acid (HCl) Dosing Pump: Glandless Diaphragms & PVDF/PTFE Selection
Hydrochloric acid (HCl) is a severely aggressive reducing acid that rapidly dissolves stainless steels through chloride pitting and stress corrosion cracking. For 30% to 35% commercial fuming HCl, glandless diaphragm pumps with solid machined PVDF (Kynar) or virgin PTFE liquid ends and ceramic check valve balls are mandatory to guarantee 100% leak-free plant safety.
Corrosion & Dosing Dynamics: Hydrochloric Acid (HCl)
Commercial hydrochloric acid (30% to 35% concentration) is volatile and emits noxious, highly corrosive hydrogen chloride gas. Metallic materials—including standard SS304, SS316, and even basic nickel alloys—suffer rapid catastrophic pitting attack due to free chloride ions (Cl⁻). Only exotic alloys like Hastelloy B-3/C-276, Tantalum, or fluoropolymers (PVDF, PTFE) withstand continuous HCl service. Furthermore, traditional packed plunger pumps cannot be used because chloride vapors attack the plunger shaft and ambient air oxidizes escaping vapors into acidic fog.
Recommended Engineering Specifications for Hydrochloric Acid (HCl)
| Parameter | JEW Factory Recommendation |
|---|---|
| Recommended Pump Type | Glandless Mechanically / Hydraulically Actuated Diaphragm Metering Pump |
| Liquid End Material | Solid Machined PVDF (Kynar) / Virgin PTFE / Hastelloy C-276 |
| Diaphragm Construction | Pure PTFE (Teflon) bonded with high-tensile EPDM backing |
| Check Valve Balls & Seats | High-purity Ceramic (Al₂O₃) / Pure PTFE with PVDF knife-edge seats |
| Gland Packing | None (100% Glandless Hermetically Sealed Chamber) |
| Vapor Locking Prevention | Built-in manual/automatic vapor degassing bleed valve |
| Operating Temperature Limit | Up to 60°C (PVDF) / Up to 100°C (PTFE) |
| Accuracy & Turndown | ±1% accuracy across 10:1 stroke adjustment turndown ratio |
Piping, Priming & Installation Best Practices
- Zero Gland Leakage Mandate: Because hydrochloric acid vapors cause catastrophic rust on adjacent steel structures and motor housings, only hermetically sealed diaphragm heads should be deployed.
- Short Suction Piping: Due to HCl’s vapor pressure, keep suction pipe runs short, straight, and oversized to eliminate suction cavitation and gas breakout.
- Degassing Valve Integration: Off-gassing chloride fumes can accumulate in the liquid head during shutdowns. Equip the discharge with a degassing bypass line back to the day tank.
- Fume Scrubber Connection: Ensure chemical tank breathers and calibration pots are piped into an acid fume neutralization scrubber.
Frequently Asked Engineering Questions
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