Pumping salt water and condensate: the technology

Safely pumping chemically contaminated wastewater

Wastewater containing salt or chemical contaminants reliably pushes standard pumps to their limits. The consequences are pitting corrosion, crevice corrosion and premature wear – often only becoming apparent after several months, but then resulting in total failure. The problem lies less with the pump hydraulics than with the choice of materials.

Where chemically contaminated water is produced

Three sources are predominant in domestic and building services engineering:

• Water softening systems: During the regeneration of the ion exchanger, saline rinse water (sodium chloride) is produced. The salt content can be significantly higher than in many industrial processes.

• Condensate from condensing boilers: The condensate from condensing boilers is acidic. When the flue gases condense, dissolved acids are formed, which cause the pH value to drop into the distinctly acidic range.

• Industrial processes: Cleaning and treatment processes produce media with varying chemical compositions.

Why chlorides and low pH values corrode standard materials

Chlorides penetrate the passive layer of standard stainless steel in specific areas, triggering pitting corrosion – a localised, difficult-to-detect corrosion mechanism that penetrates the component wall. A low pH value further accelerates the widespread attack. A standard waste water pump made of Grey cast iron or standard stainless steel is not capable of withstanding these conditions in the long term.

The materials-based approach

The answer lies in the combination of materials. In the Willy 1003 CS, the open multi-channel impeller is made of glass-fibre-reinforced plastic, which is largely chemically inert; the motor shaft and motor housing are made of highly resistant stainless steel. This enables the pump to handle chemically contaminated wastewater with a salt content of up to 15 per cent – including the relatively high-salinity regeneration water from water softeners. Solids up to 20 mm in size are no problem.

The pump is designed for occasional, often mobile use: a directly fitted float (without a cable) controls its operation, whilst a removable suction strainer, together with the float lock, enables residual water to be drained down to a depth of 5 mm, and an automatic ventilation system ensures reliable start-up. The maximum fluid temperature is 35 °C, and the head is approximately 10.5 m.

Conclusion

In the case of saline or acidic waste water, the choice of materials determines the service life. Where standard pumps corrode, a combination of chemically inert plastic and highly resistant stainless steel withstands the corrosive attack. The specific choice will depend on the salt content, pH values and temperature of the medium.