At the 33rd Queensland Water Industry Operators Association Workshop on The Gold Coast recently, a simple competition for Operator Teams has ignited a debate, which challenges the norm of using submersible pumps in sewage pumping stations.
The operators were asked on one exhibitor stand to overhaul a Gorman-Rupp self priming sewage pump, where the winners competed the task in just two minutes and thirty three seconds.
Ron Watts, spokesperson for Hydro Innovations , exclusive distributors for Gorman-Rupp in Australia, said that 13 separate teams competed in the event, including self confessed desk jockeys and pen pushers, and none of the teams took longer than 4.25 minutes to complete the overhaul task.
Ron Watts said that several teams were surprised at how easy the pump was to work on and many commented on how easy the pumps would also be to access, being located at up to 6.5 metres above the sewage, with no mechanical equipment actually needing to be in the wet well at all.
Ron Watts advised that many who competed and some spectators cited several reasons why self priming pumps would have many advantages over the use of submersibles in pump stations.
In summary, these included reduced O.H.&S issues, reduced maintenance costs and reduced inventory support needs.
With OH&S issues, Ron Watts said that most recognised that with self priming pumps there would be no need to open wet well lids and no need to enter the wet well at all.
Submersible pumps, on the other hand, throughout their service life, will need many wear ring changes, discharge elbow replacements, guide rail replacements etc, all requiring wet wells to be opened and exposing service personnel to confined spaces issues and associated dangers.
With inventory issues, Ron Watts said that most participants were surprised to learn that all pump duties from 10 litres per second through to 150 litres per second and all pump heads to 30 metres could be covered with just 5 Gorman-Rupp pump models, making the stocking of support inventory quite inexpensive.
In contrast, he said that some Councils and Water Authorities at the workshop spoke of having as many as 100 pumping stations, which may require as many as 30 different pump models and numerous different impeller trims to meet the many specific duties.
Cost of maintenance was, however, a glaring difference between the pumping styles according to Ron Watts. All participants were shown how easy it was to adjust the tolerances of a Gorman-Rupp Super T Self Priming Centrifugal Pump.
Ron Watts said that all were shown that internal impeller/wearplate clearances could be adjusted in under 5 minutes and without having to disconnect piping or drive unit. It is the opening up this clearance that causes a decrease in efficiency and an increase in blockages from stringy materials such as rags, plastics and underwear.
With submersible pumps, to minimise the loss in efficiency and decrease the incidence of blockages, the power needs to be disconnected, wet well lids need to be opened, a lifting device needs to be employed to lift the pump out of the wet well, the pump then needs to be cleaned, wear rings need to be chiselled out, new wear rings installed, the pump then needs to be lowered back into place.
Ron Watts added that with the Gorman-Rupp alternative, operators could keep tolerances tight (keeping pumps at their highest efficiency and reducing blockages) through up to 6mm of adjustments before an impeller or wear plate needs to be replaced.
He asked WIOA visitors to contrast this to submersible pumps which keep losing efficiency and increasing chances of blocking as tolerances keep opening up until wear rings and/or impellers need replacing.
Ron Watts says that while Gorman-Rupp pumps can be kept at 0.3mm clearances for the life of their wearing parts, submersible pump manuals recommend wear ring replacement when clearances reach 2.0mm, a tolerance Ron Watts maintains will attract blockages and cause pump to run at well below best efficiency.
Ron Watts said that delegates were also impressed with the new High Performance, High Head addition to the Gorman-Rupp range, the Ultra V. He said this new pump was the latest technology in self priming solids handling pumps, with heads capable of reaching 90 metres and new patented systems capable of handling stringy materials vastly better.