At our plant site, we have a steam turbine that operates a water pump through a step-down gearbox. Connected to the intermediate shaft of the gearbox is the primary lube oil pump. During startup, an auxiliary motor-driven lube oil pump is used. When gradually increasing the turbine speed from 1000 to 6000 rpm, the main lube oil pump struggles to take on the load and experiences overheating. However, when the turbine speed is rapidly increased, the pump is able to handle the load effectively. The main lube oil pump is positioned 1 meter above the oil console. Could the issue be related to suction lift problems?
It appears that there may be an issue with air getting sucked into the suction line, gear slippage on the shaft, or excessive internal clearances in the pump. These possible problems should be addressed to ensure optimal pump performance.
From your description, it does seem like you could be facing suction lift issues. Typically, the greater the suction lift, the lower the capacity of the pump. Your oil pump may be working harder at lower speeds due to the pressure differential created by the suction lift, causing it to overheat. Conversely, as you ramp up the speed quickly, momentum helps overcome the suction resistance, thus the pump doesn't struggle as much. My suggestion would be to either lower the pump closer to the oil console or consider the installation of a self-priming pump. However, I might also recommend checking all parts of the system for inefficiencies before making major changes. Things like worn seals, misalignment, or oil viscosity could also contribute to the issue.
It does appear that your oil pump might be dealing with suction lift issues. Given that the main lube oil pump is positioned a meter above the oil console, when the turbine speed is gradually increased, it might not generate enough pressure initially to efficiently lift and circulate the oil, causing it to overload and overheat. When the speed is rapidly increased, the pump quickly generates enough pressure to surmount the lift, hence operating effectively. You might want to consider repositioning the pump or alternatively, employing a booster pump to alleviate the suction load during startup.
It does seem like the pump may be experiencing issues related to suction lift, especially since it's positioned 1 meter above the oil console. However, the challenge doesn't seem to persist when you rapidly increase the turbine speed, leading me to think about other potential variables. One factor could be the viscosity of the oil. For example, when the turbine speed is gradually increased, the temperature of the oil rises slowly which can increase its viscosity and make it harder for the pump to operate. Conversely, a rapid increase in speed might not give enough time for the oil to heat, retaining its lower viscosity and allowing easier pumping. I would suggest checking the oil's viscosity at various temperatures to see if this could be an underlying issue. Also, consider the possibility of air entrainment or the formation of vapor bubbles due to lower pressure, which could be disturbing the oil flow and causing overheating.
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Answer: - The main lube oil pump may struggle due to suction lift problems, especially since it is positioned 1 meter above the oil console.
Answer: - Rapidly increasing the turbine speed may help overcome the suction lift issues, allowing the pump to handle the load more efficiently.
Answer: - Suction lift problems can lead to issues with pump priming, cavitation, and inadequate flow rates, which can affect the overall performance and efficiency of the gear pump.
Answer: - Potential solutions may include adjusting the pump's position to reduce suction lift, optimizing the piping layout for better flow, or considering the use of a different type of pump that is better suited for the application.
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