Oranmore Pumping Station
Oranmore Sewerage Pumping Station was a troublesome station for Galway County Council with the existing dry well pumps having to be refurbished every few years. The replacement of bearings, wear rings, seals and even impellers was commonplace since the initial installation 10 years previously. DPS were called in to find out the reason why the parts needed replacing so frequently.
After an investigative site visit, it was agreed that the pumps should be brought to the DPS workshop for further inspection.
When the pumps were stripped from the bottom up, the first signs of wear were visible on the outside of the impeller eye which, in all 3 cases, had been running to a greater or lesser extent, against the wear ring on the base of the volute. This indicated bearing wear that permits the shaft to move off the centre line. In two of the units, wear was visible but not extensive. The third unit had significant wear. Any wear incurred on a pump impeller results in an imbalance which increases bearing load and subsequent failure.
Single channel impellers are principally designed for solids handling capability rather than superior balancing and are therefore set strict parameters for operation. A combination of pump units in a series application and, operating in conjunction with a variable speed drive, can lead to difficulties with reliability. Further stripping of the pumps showed significant bearing wear and damage which had, in two of the three cases, resulted in bearing housing damage. In the other case the shaft was completely sheared.
For these reasons, and from the extensive repairs required, DPS recommended that all four pumps be replaced with new units. DPS also detailed a new control philosophy that set a more regimented pumping regime and removed the feed forwarding variables that we believed contributed to the difficulties experienced on site.
Previously, the pump in each series was operated at various speeds and not in conjunction with the other pump in its series. The first pump would operate for any length of time and the second pump would come into operation only if the volume of effluent increased. The pumps in series would alternate in this manner. By operating on its own for long periods of time, each pump would increasingly lose balance and cause wear in the parts described previously and, ultimately, fail.
The Council ordered new pumps and adopted an automated control philosophy. If both pumps were not running within a few seconds of eachother, the system shuts down to prevent damage to either of the pumps. DPS guaranteed the Council smooth operation of the new system under the new control philosophy and, to this day, the pumps are running at maximum efficiency without the need for any further troublesome repairs.