When a shielded pump is operating normally, will the flow rate at the outlet increase or decrease when it is set to maximum flow?
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Today, one of the canned pumps suddenly didn’t perform as well as usual. Upon inspection, it was found that the pressure at the pump’s outlet was too low. After restarting the pump and reducing the opening of the outlet valve, its performance returned to normal. However, when I tried to increase the outlet opening to its previous higher level, the pump’s pressure didn’t change, and the flow rate continued to increase. Why is there such a big difference in performance for the same pump at the same opening level? Also, I would like to ask whether the outlet opening of a canned pump can be increased to its maximum
Cavitation occurs; when the flow rate at the outlet is increased, the flow velocity rises as well, and the pump’s net positive suction head also increases. Once the flow rate reaches a certain level, the device’s net positive suction head is no longer sufficient to prevent cavitation. Cavitation will occur in the pump. There will be a cracking sound inside the pump casing. The outlet pressure has dropped.
Then why, after that, was the experiment run for another ten minutes with no decrease in flow rate and no noises?
This is related to your inlet pressure; if there are changes in your inlet pressure, and the pressure is high, an increase in flow rate will not cause cavitation.
When a shielded pump is operating normally, opening the outlet to its maximum reduces the pressure drop in the pipeline and increases the flow rate; however, opening it too wide can cause the motor to burn out.
“When the shielded pump is operating normally, the outlet is opened to its maximum extent............... But no matter how further it is opened, the motor can’t – it’s already at full capacity; how can it be opened any further? ~~~~~~~ In your case, the issue isn’t related to the pump~~~ It’s the conditions of the inlet pipeline that are changing, which in turn causes changes in the outlet conditions; cavitation is not necessarily the cause ； Under ideal operating conditions, the outlet of a centrifugal pump is not throttled~~~ Regulation is achieved using variable frequency
In the performance of some shielded pumps, the head curve is relatively smooth； In other words, for 80% to 100% of the flow rate, the head and pressure remain largely unchanged, and since the motor has sufficient power, it is possible to keep the outlet valve open wide, resulting in a higher flow rate ； Additionally: Generally speaking, considering only the motor matching to the opening degree of the pump’s outlet valve is not sufficient; for shielded pumps, factors such as axial force and cavitation also need to be taken into account. Therefore, it is not advisable to deviate too much from the rated values