Impact of increasing the pump outlet diameter and installing a filter at the inlet, resulting in reduced water flow, on the pump
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As the title suggests, a filter screen is installed at the pump inlet; the rated pressure is 1.0 Mpa. After starting the pump, the pressure reading was 1.3 Mpa. As the pump outlet valve was gradually opened until the pressure reached 1.0 Mpa, the pump began to make noisy noises. What harm does this phenomenon cause to the pump? What is the principle?
Adding a filter is equivalent to using an inlet control pump to regulate flow, which very easily leads to cavitation. It causes severe damage to the impeller.
Is that noisy sound caused by cavitation?
Do you mean adding another one in addition to the inlet filter that the pump already has? What is your intention in doing this? My guess is that after installing the filter screen, insufficient supply of the medium led to the pump experiencing vacuum conditions, which generated that noise; this caused severe damage to the seal
Installing a filter at the inlet reduces the diameter of the inlet pipe, while an increased diameter of the outlet pipe leads to a severe shortage in water supply, causing cavitation in the pump and preventing it from functioning properly.
At the beginning of operation, it is advisable to install a filter screen; the main purpose is to prevent residues such as welding slag and other debris from remaining after installation. I have encountered cases where a brick was left inside the pipes, and in more extreme cases, items like safety helmets and work clothes as well. Therefore, it is worth installing such a filter for a certain period after installation. As for the mesh size, 60 mesh is sufficient.
I’m not entirely sure either; when the inlet filter of our boiler feed pump gets clogged, the pump starts making squealing noises and the outlet pressure drops, so we have to shut it down immediately.
This is clearly an inlet issue; insufficient flow is causing the pump to go into vacuum. A filter was added at the inlet, increasing the resistance of the inlet pipe; this resulted in insufficient flow at the pump’s inlet, causing the pump to run dry. There were noises inside the pump, along with significant vibration, and over time this led to damage to the mechanical seal. If it is to filter out impurities, given the current pumping conditions, it is recommended not to install the filter directly at the pump inlet; instead, it can be placed on the main pipe far from the pump. This serves a filtering function without having a significant impact on the pump!
In this situation, the pump is empty, which makes cavitation extremely likely to occur. It causes severe damage to the impeller and pump casing.
Due to the resistance of the filter, the higher the filtration precision, the greater the resistance. It increases the frictional losses in the pump’s inlet pipeline, resulting in a decrease in the head of water at the pump’s inlet. As a consequence, the net positive suction head available at the installation site may be lower than the required value for the pump; this can lead to cavitation. The manifestations of cavitation include noise and vibration, erosion and damage to the flow components, as well as a decline in performance. Long-term operation has a significant impact on the service life and reliability of the pump. Moreover, if the impurities filtered by the filter accumulate over a long period of time, the resistance may increase, which could have an even greater impact on the pump. When filtration is definitely required, it is essential to ensure the inlet pressure.
What was said earlier is correct; a 60-mesh screen is sufficient. If there are many impurities, the filter will need to be cleaned more frequently.