Problems encountered with rotor pumps when unloading methanol
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The rotor pump, with a head of 80 meters and a flow rate of 100 cubic meters per hour, is used to unload methanol from train tank cars. During the first three-quarters of the unloading process, the rotor pump operates normally; however, when there is only the last quarter of methanol remaining in each tank car, the pump generates abnormal noise, the outlet pipe vibrates severely, and the flow meter shows a very low flow rate. The person from the manufacturer said that it was due to excessive cavitation, and suggested using a portable low-flow rotary pump to transfer the remaining methanol from each tank truck into one tank before using the main rotary pump for transportation; this solution is utterly unreliable. I would like to ask whether it is due to quality issues with the rotor pump, resulting in insufficient pumping capacity and severe cavitation. Coincidentally, the liquid level in the tank truck is exactly at the height of the rotor pump’s suction inlet. I hope everyone can help analyze this situation. Thank you
The process flow involves using a dip pipe with a diameter of 100 to connect the rotary pump, which then transports the fluid to the tank area via a rotary pump with high flow rate and lift capacity. The diameter of the pipe before the pump inlet is dn125, while the main pipeline for transporting methanol has a diameter of dn200. The dip pipe extends down to the collection hole at the bottom of the tank truck, and it is equipped with claws, so there is no risk of blockage at the entrance of the dip pipe; everything was normal up to three-quarters of the way along. The filter before the rotor pump is also free of debris, and it is regularly cleaned and inspected
There are very few inlet and outlet elbows on the rotor pump, and the equipment layout is good; however, the liquid level in the tank truck at the height corresponding to the rotor pump’s inlet becomes abnormal
Calculate the net positive suction head of the unit
The manufacturer is right; the diameter of the imported pipe is a bit too small. The piping must meet the pump’s design requirements! It’s hard to say without the pictures of your details.
The description was incorrect; the pump inlet pipe is 150, and the manufacturer said our inlet pipe is too thick
Regarding cavitation, verify the final pressure conditions to prevent surging due to vaporization
This post was last edited by Raindrops fall silently on 2018-9-6 at 15:55. The 1/4 inch inlet might be allowing air to enter, which causes vibration and noise; the liquid level is below the inlet level
The pipe diameter should be one size larger than the pump inlet diameter.
When the pump is operating normally, the vacuum gauge on the suction pipe shows 0.03 MPa; this indicates that the suction pressure of the pump is lower than the absolute vaporization pressure of methanol at its operating temperature. As a result, gas obstruction occurs in the pipes, causing cavitation in the pump, which in turn leads to severe vibrations at the pump’s outlet.