Side Stream Pump Overhaul & Test

THE CHALLENGE:

Torishima was tasked with the overhaul for a Side Stream Pump (Model: AZ 250-400) installed in 2002 for one of our clients. This pump had a rated power of 136kW and a pump duty of 1200m³/h generating 30m head and had a purpose of providing cooling water for side stream filtration in a cooling tower system. The customer reported pump failure due to the equipment being submerged in water, following a flood.

Upon inspection of the pump, it was found that there was a bearing failure, the non drive end bearing had collapsed, the drive end bearing was excessively worn, and the circlip could not be located. This in turn had created excessive axial movement of the shaft and the impeller had run into the suction wear ring face, causing 10mm of axial and radial wear on the end suction end of the impeller and internals of the casing. As a result, the shaft had heavy fretting on bearing locations and the shaft shoulder for the bearing is badly damaged.

THE SOLUTION:

To address these issues, Torishima supplied two new casing wear rings subject to API 610 running clearance to take up the radial gap, thus minimizing the volumetric losses. An 'L-Shaped' impeller wear ring was also supplied, recovering some of the axial wear on the impeller eye and acting as a buffer in preventing future wear in and around the area.

Consumable parts such as bearings were replaced, minimizing the vibration. Upon further inspection, it was found that it was the repeated loosening of the lock nut on the end of the shaft that caused the damage to the shaft. To prevent the impeller lock nut loosening in the future, Torishima supplied a newly designed lock nut to fit a propriety (ISO9001) 'Nord Lock Washer,' creating a wedge effect underneath the bolt head or nut.

Torishima testing the unit post overhaul, after renewal of the internal clearances and repair, the verified results found a 6% increase on the efficiency when compared to the of the original test. This highlights the excellent work carried out by Torishima engineering team and will now reduce the customer’s net spend required to operate the pump.

IMPROVEMENTS:

Improvements provided to this unit as a result of TSSE overhaul & OEM knowledge are as follows:

• New shaft supplied to the OEM standard to replace  the  existing  shaft  which  was extensively damaged.
• Balance  and  vibration  testing  to  ensure mechanical integrity of the pump and rotating elements.
• Clean up of the inboard side of the impellers fine annular clearance to a nominal size.
• New  wear  rings  to  take  up  radial  gap, minimizing volumetric losses, thus increasing efficiency.

COMMERCIAL AND ENVIORNMENTAL BENEFITS:

Torishima continually looks to provide a benefit for our customers through ease of maintenance, improved efficiency or reliability. Torishima always considers the commercial and environmental impact on any overhaul, in this instance:

*Estimating 0.2kg of CO2 emissions per KWh of wasted energy.

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