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A water treatment facility in the US recently turned to the Watson-Marlow Fluid Technology Group (WMFTG) when a new pump was needed to feed sodium hypochlorite under high pressure into its post-chlorination cycle. The previous diaphragm metering pump had serious issues with off-gassing, resulting in vapour locking that shut down the pump. After replacing the diaphragm pump with new peristaltic Qdos 20, which is specifically designed for high-pressure applications, the facility has significantly reduced downtime. Simultaneously, the pump’s fluid recovery features make it possible to avoid any chemical spills when replacing the line.
Victoria in Minnesota has around 8800 inhabitants and is located in Carver County. Residents here are supplied with drinking water from three groundwater wells. About 10 years ago, a water treatment facility was constructed to treat iron and manganese present in the water. Here, several chemicals are used in the water filtration, clarification and distribution process, including fluoride, sodium hypochlorite, polyphosphate and sodium permanganate.
Off-gassing issues
The diaphragm pump used to meter sodium hypochlorite at the post-chlorination stage was experiencing severe issues related to off-gassing. According to Clark Corbett, Sales Engineer for Vessco Inc, Victoria’s chemical feed equipment supplier, this is a common problem in such applications.
“The original diaphragm pump was losing prime, off-gassing to the point where bubbles were getting into the diaphragm and vapour locking it, so the pump stopped working,” he explains.
According to Mr Corbett, there were very few options when it came to sourcing a replacement pump that could deal with the application, which runs at relatively low flows (9-13.5 litres per hour), but high pressures (up to 7 bar on discharge). However, he pointed the water treatment works to a brand new technology, the Qdos 20 peristaltic metering pump from WMFTG.
Peristaltic pumps have no valves, seals or glands in the fluid path so are not affected by air entrainment or abrasive/corrosive fluids such as those found in water treatment. Importantly, the Qdos 20 ReNu pumphead eatures a tube material specifically formulated for high pressure sodium hypochlorite applications.
One-year trial
The Victoria plant ran a Qdos 20 trial model for more than a year – only replacing the ReNu pumphead once in that time. Operating at between 4.8 and 7 bar, and controlled by a 4-20mA input signal, the Qdos 20 pump significantly reduced maintenance downtime. As a result, the plant is currently in the process of replacing the trial model with a production unit.
Water plant operator Brady Lee says: “We like these pumps a lot. Maintenance is fast and simple, while controlling the pumps to increase flow as water demands change is very straightforward.”
WMFTG’s Qdos 20 is inherently designed to reduce maintenance. For example, the ReNu pumphead features an integrated leak detector that shuts off the pump to protect it in the event of any type of failure. Moreover, if the tube fails, operators just quickly and safely replace one component, the pumphead, without the need for tools or special skills.
The new pump has been developed to offer optimised performance life in sodium hypochlorite applications up to 7 bar at flow rates from 0.005-20 litres per hour. It is especially suitable for applications at the well sites of many smaller water treatment plants, where operators are often injecting into water lines at higher pressure.
Small plant flexibility
“Water applications need a reliable feed for chemicals, and it is especially important to keep sodium hypochlorite running,” explains Mr Corbett. “The Qdos 20 addresses the needs of small plants requiring more flexibility. Smaller towns tend to have limited maintenance personnel. With this technology, they only need to replace the pumphead, a low cost disposable part.”
Another feature liked by the plant is that the line can be replaced without spilling any chemical left in the tubing, a highly important safety feature considering that sodium hypochlorite used for this type of application is extremely corrosive.
The Victoria plant is considering acquiring a second Qdos 20 pump for its pre-chlorination sodium hypochlorite application. Also being contemplated is replacing a diaphragm pump used to meter permanganate. The long-term aim is to use Qdos technology for all of the plant’s chemical metering applications.
