The Challenge:

The South Central Connecticut Regional Water Authority faced a problem with off-gassing from sodium hypochlorite that rendered its feed pumps ineffective.

Pumps would lose prime, run dry and fail to deliver disinfectant chemicals when needed most, especially during startups when no operators were on site. The authority addressed the challenge by switching to progressive cavity pumps, improving disinfection reliability while reducing maintenance costs and callouts.

Seeking reliability

The authority serves some 430,000 residents in 15 counties, operating a network of unstaffed well fields. Inconsistent sodium hypochlorite dosing had posed a persistent challenge. At the seven well field sites, operators aim for a 1.1 mg/L chlorine residual at all times.

The existing feed pumps struggled, according to Jesse Culbertson, assistant chief operator of water treatment. “The well fields operate based on system demand, sometimes for one hour a day, sometimes around the clock,” he says. “We would find pumps airlocked from off-gassing, failing to prime and just moving air instead of chemical.”

Sodium hypochlorite naturally off-gasses when stored or pumped, creating problems for some pump types. The issue is pronounced in facilities that operate intermittently. At South Central Connecticut, some well fields run as infrequently as once per week. Inconsistent run time and pressure demands up to 120 psi created a perfect storm of dosing unreliability.

When pumps failed to dose properly, emergency callouts were required. Operators had to manually purge systems, often during nights and weekends. Looking for alternatives, Culbertson and his team tested various feed systems and pump types, including those with automatic purging features, but continued to experience problems.

Then the authority partnered with Roto Pumps for a 90-day trial of an RJCP aggressive chemical dosing pump, a progressive cavity model designed to handle corrosives, off-gassing and viscous fluids.

“We installed the pump at one well field and immediately saw a drop in our callouts,” Culbertson says. “Chlorine residuals were steady. The pump held prime between intermittent starts. It was a night-and-day improvement.” In response, the authority began standardizing on the new pump type across their well fields; it is now deployed at six of the seven sites.

Design advantages

Progressive cavity pumps are a type of positive displacement technology in which a single helical rotor rotates within a double-helix elastomeric stator. As the rotor turns, it forms sealed cavities that progress along the pump length, transporting fluid in a smooth, laminar motion.

Progressive cavity pumps are inherently self-priming even after long periods of inactivity, especially beneficial in remote or intermittent-use sites. The geometry of the rotor-stator cavity creates a smooth, low-shear fluid transfer with virtually no pulsation, ensuring steady and precise dosing.

The continuous flow path and absence of air-entrapment pockets prevent vapor lock, an issue exacerbated by sodium hypochlorite’s off-gassing. The RJCP pump allows gas to pass without disrupting the liquid feed. The pumps can handle pressures up to 350 psi without pulsation dampeners or external pressure stabilizers.

The flow rate is directly proportional to speed, enabling fine control through manual adjustment or integration with variable-frequency drives. The pumps deliver ±1% dosing accuracy to meet target chlorine residuals.

All wetted components in the pumps are constructed from corrosion-resistant materials, including optional stainless steel, Hastelloy or titanium rotors. The stator is molded with integral sealing gaskets that prevent media from contacting the stator housing or adhesives. This extends life and prevents degradation from sodium hypochlorite, an oxidizing agent known for attacking seals, coatings and elastomers.

Modular architecture also contributes to ease of service. The rotor, stator and shaft seal are easily accessible for inspection or replacement and the plug-in shaft design enables quick disassembly without disturbing pipework or motor alignment. 

The dosing pumps are designed to handle corrosive, off-gassing and viscous fluids.

 

Setting a standard

During the trial phase, the pumps early wear on some stators, but Roto Pumps worked with the authority’s team to adjust plumbing configurations. “We had to experiment with a few setups,” Culbertson says. “Once we figured out the right arrangement, we ran the pump for a long stretch with no issues. That’s when we knew we had something that worked.”

Since the new pumps were rolled out across its network, the authority has saved significantly on maintenance and downtime. Maintenance kit costs are about half those for the previous pumps. No oil reservoirs mean no risk of cross-contamination if a failure occurs. Few moving parts and easy disassembly allow operators to complete repairs with basic tools.

“When we need a part quickly, we call Roto and it gets shipped out immediately,” Culbertson says. “Even when we didn’t have the part number, just a general idea, they made sure we got what we needed.”

By maintaining prime between runs, the pumps require less attention and eliminate most night-time or weekend site visits, reducing labor costs and operator fatigue. Culbertson says operators appreciate the intuitive layout and quick-access parts.

Most important, the pumps deliver steady, accurate disinfectant dosing, helping operators set and forget dosing parameters with confidence. Whether running for an hour a day or continuously, the pumps adjust with demand. This means more consistent chlorine residuals, reducing regulatory risk.

Delivering quality

The transition to progressive cavity pumps solved more than a mechanical problem: it strengthened the authority’s ability to deliver safe drinking water reliably, consistently and with fewer staff interventions.

The experience demonstrates how a strategic shift in equipment and vendor collaboration can yield immediate and lasting gains in uptime, safety and cost control. With fewer callouts, simplified maintenance and more stable chlorine residuals, the utility has laid the groundwork for scalable, modern disinfection practices, especially in decentralized or intermittently operated systems.

“We’ve tried every pump out there,” Culbertson says. “These are the ones that worked.”

Read Full article at: https://www.tpomag.com/editorial/2026/01/off-gassing-disinfectant-a-change-of-pumps-provides-the-answer?news