Chemical Compatibility Chart for Metering Pumps | Apex Flow
A chemical metering pump is only as reliable as its wetted materials. When the pump head, diaphragm, valve balls, seats, and O-rings are matched to the fluid being dosed, a metering pump will run for years with predictable accuracy. When they are not, the result is swelling, embrittlement, cracking, loss of prime, and — in the worst case — a chemical leak. This compatibility chart helps you specify the right wetted-material package before that happens.
Apex Flow Solutions supports water treatment, chemical processing, and industrial dosing operations with metering pumps and the chemical-resistant components that go with them. The tables below summarize how the most common metering-pump materials perform against the chemicals dosed every day in those industries.
Chemistry, concentration, and temperature all change the answer. If you are dosing a blend, an oxidizer, or anything above ambient temperature, contact our team and we will confirm the right liquid-end materials before you order.
How to Read This Chart
- The A–D Compatibility Rating Scale
- Metering Pump Wetted Materials Explained
- Master Chemical Compatibility Chart
- Diaphragm & Elastomer Seal Selection
- Temperature & Concentration Effects
- Standards & References
- Frequently Asked Questions
The A–D Compatibility Rating Scale
Compatibility data across the industry uses a four-tier letter scale. The ratings in this guide follow the same convention and assume ambient temperature service near 70°F (20°C). Higher temperatures, higher concentrations, and continuous (versus intermittent) exposure all reduce real-world performance.
| Rating | Meaning | Field Guidance |
|---|---|---|
| A | Excellent | No significant effect. Suitable for continuous service. |
| B | Good | Minor effect. Suitable for most service; verify at temperature. |
| C | Fair | Moderate effect. Intermittent service only; expect shorter life. |
| D | Not Recommended | Severe effect. Do not use — swelling, attack, or failure likely. |
A metering pump liquid end. The pump head, diaphragm, valve balls and seats, and O-rings are the wetted components that must each be chemically compatible with the dosed fluid.
Metering Pump Wetted Materials Explained
"Wetted" materials are any component the dosed chemical physically contacts. On a typical diaphragm metering pump, that means the pump head (liquid end body), the diaphragm itself, the suction and discharge valve balls and seats, and the O-rings. A compatible package requires every one of these to survive the chemistry — a PVDF head with an incompatible EPDM O-ring will still fail.
| Material | Typical Component | Max Temp (Typical) | Best For |
|---|---|---|---|
| PVC | Pump head | 140°F (60°C) | Acids, caustics, hypochlorite at ambient temp |
| PVDF (Kynar) | Pump head, valve seats | 250°F (120°C) | Oxidizers, strong acids, higher temps |
| PTFE (Teflon) | Diaphragm face, balls, seats | 400°F+ (200°C+) | Nearly universal chemical resistance |
| 316 Stainless | Pump head, balls | 500°F+ (260°C+) | Solvents, fuels, high pressure — NOT chlorides/hypochlorite |
| Polypropylene (PP) | Pump head | 180°F (82°C) | Acids, bases, many salts |
| Ceramic (Alumina) | Valve balls | High | Abrasive slurries, oxidizers |
| FKM (Viton) | O-rings, seals | 400°F (200°C) | Acids, fuels, oils — NOT caustics/amines |
| EPDM | O-rings, seals | 300°F (150°C) | Caustics, ketones, hot water — NOT petroleum |
Master Chemical Compatibility Chart
The chart below rates the most common metering-pump wetted materials against the chemicals dosed most often in water treatment and industrial systems. Ratings are for ambient temperature and typical dosing concentration. A = Excellent, B = Good, C = Fair, D = Not Recommended.
| Chemical | PVC | PVDF | PTFE | 316SS | PP | FKM | EPDM |
|---|---|---|---|---|---|---|---|
| Sodium Hypochlorite (12.5%) | A | A | A | D | B | A | C |
| Sulfuric Acid (<50%) | A | A | A | C | B | A | D |
| Hydrochloric Acid (37%) | A | A | A | D | A | A | C |
| Sodium Hydroxide (50%) | A | B | A | A | A | D | A |
| Ferric Chloride | A | A | A | D | A | A | B |
| Hydrogen Peroxide (35%) | B | A | A | B | B | A | B |
| Polymer / Coagulant | A | A | A | A | A | A | A |
| Citric Acid | A | A | A | B | A | A | A |
| Aluminum Sulfate (Alum) | A | A | A | C | A | A | A |
| Sodium Bisulfite | A | A | A | C | A | A | A |
Note the recurring pattern: 316 stainless steel is excellent for solvents, fuels, and caustics but is attacked by chlorides and hypochlorite, which are the backbone chemicals of water disinfection. For most municipal and pool/spa dosing, a PVC or PVDF liquid end with PTFE or ceramic balls is the safe default.
Diaphragm & Elastomer Seal Selection
The diaphragm and the O-rings are where most "compatible-on-paper" pumps still fail, because elastomers swell and harden long before a thermoplastic head shows any damage. Most modern metering pumps use a PTFE-faced diaphragm, which is chemically near-universal. The bigger decision is the O-ring/seal elastomer, where FKM (Viton) and EPDM cover opposite ends of the chemical map.
| Seal Elastomer | Strong With | Avoid With |
|---|---|---|
| FKM (Viton) | Acids, fuels, oils, hydrogen peroxide, hypochlorite | Strong caustics, amines, ketones, hot water/steam |
| EPDM | Caustics (NaOH/KOH), ketones, hot water, mild acids | Petroleum oils, fuels, hydrocarbons |
| PTFE | Nearly all chemistries; the universal choice | Molten alkali metals, fluorine gas (rare) |
When a single pump must handle two opposing chemistries — for example a plant that alternates between caustic CIP cleaning and acid dosing on the same skid — a PTFE diaphragm with PTFE-encapsulated O-rings is usually the only package that satisfies both.
Temperature & Concentration Effects
Every rating in this chart degrades as temperature climbs. A material rated "A" at 70°F may drop to "C" at 120°F. As a rule of thumb, derate one full grade for every 30–40°F above ambient, and verify against the manufacturer's chemical resistance data for the exact concentration. Concentration matters just as much: dilute sulfuric acid is benign to many plastics, while concentrated (>70%) sulfuric acid becomes a powerful oxidizer that attacks materials it otherwise tolerates.
Two practical reminders. First, sodium hypochlorite off-gases and degrades with heat — keep it cool and use a degassing or auto-deaeration pump head to prevent vapor lock. Second, sodium hydroxide above ~40% concentration can crystallize at room temperature, so heat tracing and EPDM-compatible materials are both required for reliable caustic dosing.
Standards & References
Compatibility selection for metering pumps draws on several standards bodies. For drinking-water systems, wetted materials should carry NSF/ANSI 61 certification. Thermoplastic pressure ratings follow ASTM D1784 (PVC/CPVC cell classification) and ASTM D3222 (PVDF). Stainless steel grades reference ASTM A276, and elastomer compounds are classified under ASTM D2000. For chlorine and hypochlorite handling specifically, consult the Chlorine Institute pamphlets and AWWA guidance. These standards govern the material itself; the pump manufacturer's published chemical resistance chart governs the assembled liquid end and should always be the final authority.
A compatibility matrix at a glance: green (A) materials run continuously, yellow (B/C) need verification, and red (D) combinations should never be installed.
Frequently Asked Questions
What is the best metering pump material for sodium hypochlorite?
A PVC or PVDF pump head with PTFE or ceramic valve balls and FKM (Viton) or PTFE seals is the standard choice for 10–12.5% sodium hypochlorite. Avoid 316 stainless steel — chlorides in hypochlorite cause pitting and stress-corrosion cracking.
Can I use a 316 stainless steel metering pump for acids?
It depends on the acid. 316SS handles dilute sulfuric and most organic acids reasonably well, but it is rapidly attacked by hydrochloric acid, ferric chloride, and any chloride-bearing solution. For those, use PVC, PVDF, or PTFE wetted parts instead.
Why did my metering pump diaphragm swell and crack?
Swelling and cracking are classic signs of elastomer incompatibility — the seal or diaphragm absorbed the chemical. The most common cause is using an FKM seal with a caustic or amine, or an EPDM seal with a petroleum-based fluid. Switching to a PTFE-faced diaphragm and PTFE-compatible seals usually solves it.
Does temperature change chemical compatibility?
Yes, significantly. Compatibility ratings assume roughly 70°F. As a working rule, derate one letter grade for every 30–40°F above ambient and confirm against the manufacturer's data at your actual operating temperature.
What does NSF/ANSI 61 certification mean for my pump?
NSF/ANSI 61 certifies that wetted materials do not leach harmful contaminants into drinking water. If your metering pump doses chemicals into a potable water stream, specify NSF/ANSI 61-certified liquid-end components.
Related Resources
- Metering Pump Calibration Guide — verify dosing accuracy after material selection
- Chemical Metering Pump Troubleshooting Guide — diagnose loss of prime, leaks, and vapor lock
- Common Chemical Compatibility Chart for Fluid Handling — the broader material reference
- Technical Resource Center — all selection and sizing guides
Shop related products: Metering Pumps | Chemical Metering Pumps