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External Gear Pumps from Kelair Pumps Australia

Viking doses up solution to frequent maintenance

Viking's Composite Mag-Drive (CMD) range of pumps are non-metallic, seal-less, external gear pumps, consisting of two reinforced plastic rotors inside a reinforced plastic pump housing. The pumps have broad chemical resistance and are robust and easy to assemble.

Kelair was approached to investigate the possibility of using Viking CMD pumps to improve two chemical dosing systems which were requiring frequent maintenance. The first was a hydrochloric acid (HCl) dosing system. The second was a chlorine dioxide (Cl02) dosing system.

Each of the existing systems utilised a mechanically-driven diaphragm pump with the flow rate determined via a servo-motor which adjusted the stroke length of the pump. The pipeline material was fiberglass in the case of the HCl system and PVC for the Cl02 system. Pulsation dampeners had been installed in the suction and discharge pipe-lines of each pump in an effort to reduce the pulsation generated by the pumps.

The availability of both dosing systems was necessary to the plant process, meaning that any interruption had to be promptly dealt with by the plant maintenance team.

The client reported that issues with the pulsation dampeners, pipelines, and servo-motors on the dosing systems had caused seven unplanned outages in a one-year period. Apart from the impact on maintenance, these issues had safety implications.

Application of Viking CMD pumps for these dosing applications was not without challenges. Whereas the flow rate of stroke-controlled diaphragm pumps can be accurately set throughout the operating range by varying the stroke length, gear pumps by contrast tend to be less accurate at lower pressures and flow rates due to slip of liquid through internal clearances.

A further challenge was the client's requirement for the new gear pumps to be oversized and operated at between 10-50% of their capacity using variable speed drives. Lastly the HCl pump was required to dose into a pipeline with variable back-pressure which would affect the accuracy of flow from the gear pump.

To minimise the effect of back- pressure differences on the flow accuracy in the HCl application, it was decided to run the Viking gear pump at a higher flow rate and divert some of the flow back to the tank via an existing spill-back branch in the discharge pipeline. The Cl02 pump pipeline had less variation in back pressure and it was decided that even accounting for slippage, the Viking pump would be sufficiently accurate to dose directly to the process.

To reduce the possibility of over-heating, the motors were over-sized and checks were made to ensure the motor torque would be sufficient throughout the operating range of the drives.

The Viking CMD pumps were delivered on-time and success-fully commissioned in March 2012. The pumps have operated continuously since that time.

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