Australian Water Management Review Vol 2 2013 | Page 38
Peristaltic:
first choice technology for caustic or abrasive pumping applications in the water industry
While few dispute that positive displacement (PD) pumps remain the preferred choice for metering highly caustic and corrosive chemicals, a new trend is emerging regarding pump selection. The challenge for engineers in the water industry is finding a pump that can withstand chemical attack and run reliably; can meter accurately to optimise chemical usage; and is quick and simple to maintain and operate. Meeting all three requirements, the latest peristaltic pumps are helping increasing numbers of plants reduce life cycle cost and drive gains in process efficiency.
Fit for purpose It is well documented that acidic and abrasive substances attack the valves, seals, stators and moving parts of diaphragm and progressive cavity pumps, causing disruptive downtime and high life cycle costs. By contrast, the use of peristaltic pumps allows engineers to mitigate these costs as they contain no mechanical parts in the product stream. The fluid only contacts the inside of a hose or tube, a low cost, low maintenance and easily serviceable component. Tube materials for peristaltic pumps for caustic chemical applications are today available in many different elastomers, formulated to balance mechanical pumping life with sustained resistance against acids, bases and solvents. Precise metering The inherent accuracy of PD pumps is another reason they are chosen when exact chemical metering or dosing is required – this is critical in water treatment. Peristaltic pumps provide metering accuracy better than 0.5% and flow proportional to speed. Complete tube occlusion gives them positive displacement action, preventing flow drop or erosion from backflow and eliminating the need for check-valves, which are typically the primary source of metering inaccuracy. For example, engineers at a well known WTP serving 50,000 people, Watson-Marlow’s new Qdos30 Universal Plus series metering pumps are used dosing sodium hypochlorite and sodium bisulphite. Dealing with sodium hypochlorite can be difficult as it is toxic and emits chlorine when in contact with acids. It releases tiny bubbles of gas, which tend to collect on the small ball valves found in diaphragm dosing pumps. This can cause gas locks in the system preventing the pumps from functioning. Because peristaltic pumps retain fluid completely within the
tube and have no valves that can leak or corrode, they can be used for the accurate metering of substances as challenging as sodium hypochlorite, without the associated gas lo ?????????????????????????????Q?????????????????????????????????????E??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????=?????????????????????????????????????????????????????????????????????????????????Q???????????????????????????!?????%?e???????????????????????????????????????????????]?????5????e?E??????????????????????????????????????????????????????????????????????Q????????????????????????????????????????????????????????????????????????????????1????????????????]??????????????????????????????????????????????????????????A?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
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