Will a thin inlet pipeline of the shielded pump affect its operation?
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Our company uses a shielded pump from Dalian Haimitek, model CNF80-250, with a flow rate of 60 and a head of 67.5. The motor power is 21 kW. The inlet pipeline was originally 100 mm in diameter; after it was transferred to another device, the diameter of the pipe at the storage tank outlet was changed from around 3 meters to 80 mm. Once the pump started operating, it was found that if the outlet valve was opened slightly more, the pressure would drop, from 0.4 MPa to 0.2 MPa, and the pump would produce a slight humming noise. We suspect that the section of the pump’s inlet pipeline that was replaced with an 80mm pipe is too thin, which caused the pump to run dry. Could you please advise whether this is the reason or if there are other causes? If so, how should it be modified? I wanted to add a return pipe from the outlet to the inlet, but some pump maintenance companies said that this wouldn’t work and that it’s necessary to consider the diameter of the inlet pipeline. Please give me some guidance!
Because the traffic entering your system hasn’t changed, the return line is ineffective
If you don’t want to modify the main pipeline, you can connect another DN80 pipe to the inlet
Oh, thanks! It seems we’ll have to modify the inlet pipeline
The main reason is to avoid making holes in the storage tank. It seems that adding an 80-mm pipeline would be less effective than simply modifying the existing inlet pipeline. . .
At least buffer capacity needs to be increased on the import side; it depends on which method is more convenient for you
Is there an issue with the pump model chosen? A head of 67.5M, but an outlet pressure of only 0.4MPA? I suspect you have chosen a too high head and a too low flow rate. Judging from the pump’s condition, it seems that the inlet flow is insufficient; this could be due to a clogged filter, or it might be because the liquid level in the pipelines or tank is below that of the pump. However, your model is 80-250 – is the inlet pipe standardly DN80?
0.4MPA is the current operating pressure, as this pump was transferred from another location; the designed pressure before was supposed to be 2.0MPA. The filter has been checked and there are no issues. I initially thought that this pump model came standard with an outlet size of 80, but after asking a technician from Hamilton, I learned that for Hamilton pumps of this type, the outlet size is 80, while the inlet size is 100. . Now, it is planned to connect the inlet pipeline of the other pump in the storage tank in parallel with this pump; that should be sufficient.
It seems that cavitation has occurred; increasing the diameter of the inlet pipe is the simplest solution. Do you still want to lower the pump centerline height? Increase the height of the liquid-absorbing container? I estimated that the inlet flow velocity is around 3 m/s, which is quite high