Chemical Resistant Dosing Pump Selection: PVC, PVDF, PTFE or 316 SS Heads

A pump head that turns chalky, a diaphragm that blisters, a valve seat eaten away at the edge: nine times out of ten the material was wrong. Buyers shopping for a chemical resistant dosing pump tend to ask one thing, "what is the head made of?" But the head isn't the only part sitting in the chemical. The diaphragm, valve seats, balls and seals are wetted too, and if any one of them gives up, the pump leaks or loses accuracy. Below we go through the four common head materials, PVC, PVDF, PTFE and 316 stainless, and where each one belongs.

A Chemical Resistant Dosing Pump Is the Whole Liquid End

Look at metering pump wetted materials as a set. NEWDOSE solenoid pumps, for example, offer five liquid end combinations:

PPV: PP head, PTFE diaphragm and seats, ceramic balls, FKM seals;
PVT: PVC head, otherwise the same;
PVDF: PVDF head, otherwise the same;
SST: SS316 head, PTFE diaphragm, SS316 seats and balls, FKM seals;
PTFE: PTFE head, diaphragm and seats, ceramic balls, no elastomer seal.

The diaphragm is PTFE almost across the board. What really changes is the head, the seat and ball pair, and the seals. So when you send an inquiry, give chemical name, concentration and temperature, and the supplier can check the full set rather than one part.

PVC: The Default Chemical Resistant Dosing Pump Head for Water Treatment

PAC, dilute acids and caustic, sodium hypochlorite at normal strength: for room-temperature water treatment chemicals, PVC is the most common head. Its weak point is heat. Some supplier data gives PVC wetted parts a range of 0 to 50 °C, so if the solution runs warm or the dosing room gets hot in summer, don't run PVC at its limit.

Clear PVC heads have a bonus: you can see air bubbles inside, which makes priming and troubleshooting easier.

PVDF: Step Up When Temperature or Strength Is Uncertain

PVDF handles both chemicals and temperature noticeably better than PVC. At normal strength PVC is fine, but with warmer solution, fluctuating concentration, or stronger hypochlorite, PVDF is the safer chemical resistant dosing pump head. If you can't decide between the two, we usually lean toward PVDF, especially where each delivery of chemical arrives at a slightly different strength.

PTFE: The Fallback for Aggressive or Mixed Chemicals

PTFE copes with almost anything: strong oxidizers, blended products, industrial waste streams nobody can fully describe. A full PTFE liquid end is the low-stress option, and the NEWDOSE PTFE set even drops the elastomer seal, removing one more part that could be attacked.

The downside is that PTFE parts are harder to machine, so on a chemical resistant dosing pump it is normally chosen only when PVC and PVDF can't cope, not as a starting point.

316 Stainless: Usually Not for Chloride Chemicals

Many people assume stainless steel is the most chemical resistant dosing pump material. It isn't, at least not for chlorides. For chloride-bearing chemicals such as PAC, sodium hypochlorite and hydrochloric acid, an SS316 head is generally not recommended, because chloride causes pitting.

Stainless belongs elsewhere: some organic solvents, hotter liquids, and higher pressures where plastic heads aren't suitable. Some supplier data rates stainless wetted parts up to 80 °C, well beyond PVC. The NEWDOSE HND high-pressure mechanical pump uses an SS316 head and reaches around 30 bar.

Check the Selection Table Before Buying a Chemical Resistant Dosing Pump

Not every series offers all four heads, so confirm it on the selection table. For NEWDOSE mechanical diaphragm pumps:

NDJ, NDWS, NDWL: PVC, PVDF, PTFE and SS316 are all available;
ND1000, ND2000: documentation lists PVC, PTFE and SS316, but no PVDF;
HND: SS316.

The model code spells out the material. In NDWL-410-0.6-PVT-A-H, PVT is the PVC liquid end, A is a standard three-phase 380 V motor, and H is manual adjustment. Read that string and you know exactly what the wetted parts of a chemical resistant dosing pump are. The small-flow Evodose stepper range offers PVC, PVDF, PTFE and SS316 heads, and the logic is the same.

What to Put in a Chemical Resistant Dosing Pump Inquiry

To get metering pump wetted materials checked properly, include:

Chemical name, with components listed for blends;
Concentration, not just "industrial grade";
Solution temperature and dosing room temperature;
Whether the liquid carries particles or crystallizes;
What is used to flush the lines.

That last one catches people out. Some sites dose caustic every day and flush with acid now and then, so the head has to tolerate both. Piping, injection valves and back pressure valves need matching materials as well. Get the head right and the injection valve wrong, and it still leaks.

Conclusion

Choose a chemical resistant dosing pump by the whole liquid end, not the head alone. PVC suits ambient water treatment chemicals, PVDF is the step up for heat or uncertain strength, PTFE handles aggressive and complex chemicals, and SS316 generally stays away from chlorides but fits solvents, heat and high pressure. Check that your chosen series actually offers that head, and confirm temperature, concentration, flushing chemicals and accessory materials at the same time.

FAQ

Which chemical resistant dosing pump head suits sodium hypochlorite?

Normally PVC or PVDF, with PVDF for higher strength or temperature. Stainless is not recommended.

Can concentrated sulfuric acid go through a PVC head?

Check it separately. PVDF or stainless heads are usually considered, and seal material must be confirmed too. Don't carry over experience from dilute acid.

Will a PTFE chemical resistant dosing pump handle anything?

Its chemical resistance is the best of the four, but temperature and pressure still matter, and liquids with particles need the right valve design. Send the full duty for confirmation.

My head turned white after six months. Is it the material?

Most likely the material doesn't match the chemical or temperature, or the real concentration is higher than first quoted. Check actual strength and temperature before changing material.

My chemical isn't on the selection table. What now?

Tables list materials, not every chemical. Send name, strength and temperature to the supplier for a compatibility check.

Send your chemical, strength, temperature, flow and pressure, and contact us to get the head and accessory materials specified together.