Due to the aforementioned rotor sag (along with friction from the mechanical seal faces and bearings), there will be contact between rotating and stationary components. However, the resistance should not be excessive, which would indicate mechanical interference between rotating and stationary parts. Once the rotor is turning, a competent repair facility will be capable of determining whether the rotor is turning freely or is inhibited by mechanical interference, which could cause premature failure of the pump.
Results of Retrofit
The boiler feed water pump in Alberta has been running since June 2007 and the retrofit has delivered everything plant personnel wanted:
- One pump now meets full load production demands.
- Risk of metal to metal seizure is dramatically reduced.
- The pump is running with very low vibration compared to previous levels.
As an added bonus, amperage draw on the motor has fallen by 5 percent. Using the rated power of 317-hp (237-kW) and assuming a power cost of $0.06/kWh (a typical price in North America), this is worth a lot of money: For this one pump, the plant will save roughly $6,200 for every year of operation.
The benefits of running a pump with reduced clearance at the wear rings and similar components are well documented by field studies and pump design texts. Composite materials allow pump repair facilities to reduce the clearance at the wear components to values substantially less than the recommended minimums for metal components as listed in API 610.
Furthermore, the latest generation composites have material properties which can stand up to tough services, process upsets, and off-design operation, reducing the risk of pump failure.
Quality pump overhaul practices help deliver the full benefit of composite materials with reduced clearance. Thorough component inspection, verification of rotor concentricity within the case, and proper composite installation methods contributed to the success of this application.
- Aronen, R., Boulden, B., and Russek, M., 2007, "Driving Pump Reliability Forward with Advanced Composite Wear Rings," Proceedings of the 23rd International Pump Users Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, Texas, pp. 15-19.
- Bloch, H. P., 1988, Practical Machinery Management for Process Plants Volume 1: Improving Machinery Reliability, Second Edition, Houston, Texas: Gulf Publishing Company.
- Bloch, H. P. and Geitner, F. K., 1985, Practical Machinery Management for Process Plants, Volume 4: Major Process Equipment Maintenance and Repair, Houston, Texas, Gulf Publishing Company.
- Komin, R. P., 1990, "Improving Pump Reliability in Light Hydrocarbon and Condensate Service With Metal Filled Graphite Wear Parts," Proceedings of the Seventh International Pump Users Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, Texas, pp. 49-54.
- Lobanoff, V. S. and Ross, R. R., 1992, Centrifugal Pumps: Design and Application, Second Edition, Houston, Texas: Gulf Publishing Company.
- Pledger, J. P., 2001, "Improving Pump Performance & Efficiency with Composite Wear Components," World Pumps, Number 420.
Pumps & Systems, November 2007