Pumping chemical or aggressive water safely: how to choose the right pump
David MeijerQuick answer: with chemical or aggressive water, first determine exactly what is in the water: which substance, which concentration, which pH and which temperature. Then choose a pump whose wetted parts and seals are resistant to it, usually stainless steel 316 (1.4401/1.4436) with Viton (FKM) seals. If flammable vapours are present, you need an ATEX version. If in doubt, call us before you order.
First the medium, then the pump
“Chemically resistant” does not exist in general terms. A pump that handles acidic condensate perfectly well can start leaking within weeks in a solvent. That is why the choice always starts with four questions:
- Which substance? Salt, acid, lye, oil, solvent, cleaning agent. The product's safety data sheet (SDS) gives the composition.
- Which concentration? Rinse water with a few percent of cleaning agent is something very different from the concentrated product.
- Which pH? Neutral is 7. Below 5 or above 10 it becomes critical for ordinary materials.
- Which temperature? Heat accelerates any chemical attack. Many submersible pumps are built for a maximum of 35 to 40 °C.
Materials and seals
| Component | What to look for |
|---|---|
| Pump housing and impeller | Stainless steel 304 for mildly aggressive water, stainless steel 316 for chloride and acids, plastic (glass-fibre reinforced) for salt and many acids. Cast iron only for neutral water. |
| Motor shaft | Often the weakest point. For harsh media, a duplex shaft (1.4462) or titanium. |
| Shaft seal | Silicon carbide against silicon carbide (SiC/SiC) is hard and highly chemically resistant. Carbon against ceramic is more sensitive. |
| O-rings and gaskets | NBR (nitrile) is standard and good against oil, but not against many acids and solvents. Viton (FKM) can handle much more. |
| Cable | Standard rubber cable swells in oil and solvents. Ask for a resistant sheath. |
The weakest link determines the service life. A pump made entirely of stainless steel 316 with an NBR gasket will last in a solvent only as long as that gasket.
Common situations
- Condensate from a condensing boiler or heat pump is slightly acidic (pH around 3 to 4). A small pump with a stainless steel motor and plastic housing, such as the HOMA Bully CH150 WA, is made for this.
- Salty rinse water from a water softener and brine will eat through an ordinary dirty water pump within a few years. Here too, choose a CH version.
- Process wastewater from the food industry, breweries, laundries or electroplating companies: a fully stainless steel pump with a large free passage, such as the HOMA CTP50 (stainless steel 1.4436, duplex shaft, SiC/SiC, Viton, pH 3 to 14).
- Mildly chemically contaminated water with sand on a construction site or during remediation: the SPT SPTE 370W in stainless steel with double jacket cooling.
- Seawater or salt water with chemicals: stainless steel 316, such as the Tsurumi 50SFQ2,75. See also pumping salt or brackish water.
Take care with flammable substances
If fuel residues, solvents or gases get into the water, the space above the water may be an explosion hazard zone. An ordinary pump is not permitted there, however resistant its materials may be. You then need an ATEX version as well as a suitable control panel and level switch. View the explosion-proof pumps and submit the zone classification to your safety expert.
Pumps for chemical and aggressive water
CONDENSATE AND BRINE
HOMA Bully CH150 WA
Stainless steel motor, plastic housing, automatic float switch, 230V.
View current price
STAINLESS STEEL, ALSO ABRASIVE
SPT SPTE 370W
Stainless steel pump with SiC seal and double jacket cooling, optionally with float switch.
View current price
STAINLESS STEEL 316
Tsurumi 50SFQ2,75
Pump housing in stainless steel 316 for chloride and acids, 25.7 m³/h, 400V.
View current price
PROCESS WASTEWATER
HOMA CTP50
Stainless steel 1.4436, duplex shaft, SiC/SiC and Viton, pH 3 – 14, 50 mm free passage. Also available as ATEX.
View current priceView all pumps for chemical and aggressive water or the stainless steel pumps.
Frequently asked questions
Which pump for chemical water?
A pump whose housing, impeller, shaft and seals are resistant to the substance, the concentration, the pH and the temperature of your water. Usually that means stainless steel 316 with a SiC shaft seal and Viton O-rings.
Is stainless steel always chemically resistant?
No. Stainless steel 304 is sensitive to chloride and strong acids. Stainless steel 316 is more resistant, but it has its limits too. Also check the gaskets: they often fail before the metal does.
Which pump for condensate from a central heating boiler?
A small submersible pump with a stainless steel motor and plastic housing, such as the HOMA Bully CH150 WA. Condensate is slightly acidic and attacks cast iron.
When do I need an ATEX pump?
When flammable vapours, gases or liquids can occur in or above the water, such as fuel residues or solvents. The zone classification then determines which version is mandatory.
Not sure whether a pump can handle your medium?
Send us the safety data sheet, or the substance, concentration, pH and temperature. We will compare it with the manufacturer's material data before you order.
Ask for free adviceView pumps for chemical water