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	Typical machinery piping system

Southwest Research Institute (SwRI) has identified and solved many different types of pump problems for nearly 40 years. The following summaries describe some of the serious problems SwRI has helped clients with:

• Jetting Pump Rotor Critical Speed Problems

  Jetting pumps on a large bury barge began experiencing high shaft vibrations after initial satisfactory operations. Investigation and calculations indicated that as shaft and impeller seal wear occurred, the first lateral critical speed lowered to operating speed. Bearing and shaft modifications were made to alter the rotor critical speed so that the lateral critical speed would not become coincident with operating speed as the seals wore and reduced their stiffness contribution to the rotor.

• Pressure Pulsations in Pump Crossovers

  A major crude oil pipeline company experienced high noise and vibrations resulting in seal oil piping failures and increased rotor vibrations. The problem was identified as an acoustic resonance of the external crossover between the first and second stages excited by impeller vane pass. The solution included modifying the external crossover so that it would not be excited by impeller vane pass over the speed range of the turbine driver.

• Sea Water Cooling Pump Motor and Discharge Head Vibrations

  A large electric power generating plant had high motor vibrations resulting in trips of the pumps. Field investigation and modeling revealed that there was a mechanical resonance involving the motor, discharge head and roof of the pump sump structure. Structural modifications involving tying all three pumps together resulted in a detuning of the individual pump resonant responses allowing the pumps to operate with low vibrations.

• Impeller Vane Tip Failures

  A nuclear power plant had repeated booster pump impeller vane tip failures after an overhaul. Pressure pulsation and vibration data were taken and showed that discharge pressure pulsations were significantly higher than an adjacent pump. Measurement between the impeller and pump cutwater were less than 2 percent of the impeller radius. The cutwater/impeller gap was increased to 6 percent of the impeller radius based on head end capacity calculations and the pump was operated satisfactorily without further impeller failures.

• Identification of Bearing Housing Resonance

  A large chemical plant experienced high outboard bearing vibration problems at five times running speed or impeller van pass frequency. Impact response analysis identified a mechanical resonance of the bearing housing at five times running speed. The bearing housing was modified by stiffening the external portions, shifting the resonant response to between 5 and 6 times running speed. The pump then operated with low bearing housing vibrations.

For more information about SwRI's full range of capabilities and experience in machinery vibration services or how you can contract with SwRI, please contact  Robert J. McKee at rmckee@swri.org or (210) 522-3000.   Give us the opportunity to become an extension of your engineering department.

| Fluids Engineering Department | Mechanical & Materials Engineering Division | SwRI Home |

Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

November 04, 2008