What are the reasons for high vibration in shielded pumps?
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Hello, sea friend! Dalian Empire shielded pump, single-stage; medium: liquefied gas/propane. Problem: excessive vibration when starting the pump. Upon inspection, it was found that the thrust disk on the pump side was severely worn, the shaft sleeves were worn to varying degrees, and the bearings were damaged. Both pumps handling different media exhibited this issue. Manufacturer’s analysis: The size of the balance holes may be inappropriate, leading to increased thrust and rapid wear of the thrust disk; given the conditions at the site, incomplete exhaust can be ruled out as a cause. Question: The inlet pressure of the pump has decreased compared to before – it used to be 1.0 MPA but is now 0.7 MPA. I wonder whether this drop in inlet pressure could affect the thrust on the impeller
This post was last edited by 764970655 on 2016-3-9 at 11:56. Low pressure in the inlet pipeline can lead to cavitation; it is also a cause of severe wear on the thrust disc, varying degrees of wear on the shaft sleeves, and bearing failure. It is recommended to measure the vibration intensity; under normal conditions, operation should be possible as long as it is below 2.0 mm/s.
Regarding the change from 1 Mpa to 0.7 Mpa, I would say that cavitation occurs when the suction pressure is lower than the saturated vapor pressure of the medium. Cavitation is one factor; other possible causes to investigate include shaft misalignment and poor coaxiality in the foundation installation.
The size of the balance hole can lead to an increase in thrust; in addition, factors such as whether the temperature of the medium in use is high and whether the cooling system is adequate also play a role
The temperature of the medium does not change much, and it is at room temperature (ambient temperature); the cooling method is counterflow cooling.
Before starting the pump, we need to release air and conduct inspections; the same situation occurs when a new pump is installed, even though it worked fine before.
First, analyze the reasons from the perspective of the operation itself: Has the purging of the inlet pipeline ensured that the liquid medium being transported does not wash away metal particles or other impurities?； The inlet filter screen should not be too fine; a magnetic filter is preferred ； Fill the tank with liquid before starting the pump (pay extra attention when the inlet is under negative pressure) ； The inlet pressure cannot be reduced arbitrarily. Secondly, from a manufacturing analysis perspective: the size of the balance holes may be inappropriate, which leads to an increase in thrust and rapid wear of the thrust disk. Given the conditions on site, incomplete exhaust can basically be ruled out. The pressure at the pump inlet has decreased compared to before – it was 1.0 MPa previously but is now 0.7 MPA. A decrease in inlet pressure lowers the saturated vapor pressure of the liquid, increasing the risk of cavitation, which in turn affects the thrust on the impeller.
Try increasing the inlet pressure; if that doesn’t work, then the balance hole needs to be adjusted
I’ve encountered this situation before as well; check to see if the shafts are misaligned
Could you analyze the reasons for shaft misalignment? This phenomenon occurs quickly after installing new pumps or pumps that have been repaired.
We also use Dalian shielded pumps to discharge liquid ammonia; such pumps work fine in winter, but certainly not in summer. Also, if liquid ammonia at 0.7 Mpa is transported at room temperature, it will definitely vaporize at the pump inlet; therefore, it is normal for the pump to get damaged. Suggestions: 1. Pressurize the ammonia tank to above 1.0 Mpa (be mindful of the tank’s design pressure and the setting pressure of the safety valve; do not exceed these limits) ； 2. Replace it with a sliding vane pump (domestic ones are cheap and of good quality); there are many such pumps available in Shandong. For more details, search on Baidu ；