Selecting the right pump for corrosive chemicals is not just about picking a pump that moves liquid; it is about picking a pump that won't dissolve and won't leak.
The process involves a strict sequence of decisions. Here is a step-by-step guide to making the correct choice:
Step 1: Know Your Chemical (The "Hazard" Assessment)
Before looking at pumps, you must define the liquid's properties. This determines the safety requirements.
* Corrosiveness: Is it an acid (pH < 7) or a base (pH > 7)? (e.g., Hydrochloric Acid vs. Caustic Soda).
* Toxicity/Flammability: Is it dangerous if it leaks? (e.g., Chlorine gas is lethal; Benzene is explosive).
* Viscosity: Is it thin like water or thick like syrup?
* Solids: Does it have particles (slurry) or is it clean?
Step 2: Select the Pump Type (The "Mechanism")
Based on the chemical's behavior, choose the pump style:
* For Thin, Clean, Toxic/Flammable Liquids:
Choice: Magnetic Drive Pump or Canned Motor Pump.
Why: Seal-less design. No mechanical seal means zero chance of leakage. This is the gold standard for safety.
* For Thin, Non-Hazardous Liquids:
Choice: Standard Centrifugal Pump (with a good mechanical seal).
Why: Cheaper and easier to maintain.
* For Thick Liquids (High Viscosity):
Choice: Gear Pump or Progressive Cavity Pump.
Why: Centrifugal pumps cannot generate enough force to move thick chemicals.
* For Dirty Liquids (Slurry):
* Choice: Air-Operated Double Diaphragm (AODD) or Peristaltic Pump.
* Why: They can handle solids without clogging.
Step 3: Select the Material of Construction (The "Armor")
This is the most critical step. If you get this wrong, the pump will fail in days or hours. You must consult a Corrosion Resistance Chart.
Common Chemical Pump Materials:
1. Thermoplastics (Plastics):
* Polypropylene (PP): Low cost. Good for acids and alkalis. Limit: Low temperature resistance.
* PVDF: Stronger than PP. Better for higher temperatures and UV light.
* PTFE (Teflon): The "King" of corrosion resistance. Handles almost everything (including hydrofluoric acid). Used as a liner inside metal pumps or as the pump body itself.
2. Metals:
* 316 Stainless Steel: The standard for mild chemicals and food. Fails with chlorides (salt water).
* Alloy 20: Good for sulfuric acid and other mixed acids.
* Hastelloy (C276): The "Super Alloy." Extremely expensive but handles the most aggressive chemicals (strong oxidizers, wet chlorine).
* Titanium: Excellent for chloride solutions and seawater.
The Rule of Thumb:
* Strong Acids (H2SO4, HCl): Use PTFE, PVDF, or Alloy 20.
* Strong Bases (NaOH): Use PP, PVDF, or 316 SS.
* Salt Water / Chlorides: Use Titanium or Hastelloy.
* Everything Else: Check the chart.
Step 4: Select the Seal (If using a Standard Centrifugal Pump)
If you didn't choose a seal-less (Mag-drive) pump, you must protect the shaft.
* Single Mechanical Seal: For non-hazardous chemicals.
* Double Mechanical Seal: For hazardous chemicals. If the first seal fails, the second one holds. Usually requires a flush plan (API Plan 53 or 54) to keep the seal faces cool.
* Seal Materials: The faces of the seal must also be chemical resistant. Common pairings: Carbon vs. Ceramic or Silicon Carbide vs. Silicon Carbide.
Step 5: Calculate the Duty Point (Flow & Pressure)
You need to know how much liquid you need to move (GPM/LPM) and how hard you need to push it (Head/PSI).
If the chemical is very thick (viscous), you will need a larger motor than you would for water.
Summary Checklist
* Is it Toxic? -> Mag-Drive.
* Is it Thick? -> Gear Pump.
* Is it Acidic? -> PTFE/PVDF.
* Is it Chloride? -> Hastelloy/Titanium.
* Check the Temperature! (Plastics melt; Seals dry out).
Final Advice:
Always consult the pump manufacturer's IOM (Installation, Operation, and Maintenance) manual and their specific chemical resistance guide. If you are unsure, over-engineer (choose a more expensive, more resistant material) rather than risk a leak.