Regarding the reverse circulation pipeline of shielded pumps
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Dear experts, I am working on a project where a reverse circulation pipeline for the pump is being used (mainly because the medium pumped by the pump tends to vaporize). The manufacturer of the canned pump recommends using such a reverse circulation pipeline to prevent cavitation in the pump, and it is required that this pipeline enter the gas phase area of the storage tank. Have any professionals encountered similar problems before? Please let me know how to resolve them.
The reverse circulation pipeline of the canned pump serves to cool and lubricate, reducing the temperature of the shaft; to a certain extent it can help prevent cavitation, but it is not a fundamental solution. To prevent cavitation, the key lies in the selection of pumps and motors, as well as the calculation of the cavitation margin and the inlet suction height.
If cavitation is likely to occur once all the equipment has been installed, the simplest solution is to increase the operating pressure of the pump inlet tank or tower.
The function of the reverse circulation line is primarily to flush and cool the stator and rotor temperatures, as well as to cool the shaft end bearings. It prevents equipment damage due to high temperatures and stops the medium from vaporizing at high temperatures, which could otherwise cause the pump to become evacuated. Therefore, the gas phase must be returned to the storage tank; generally, it is returned to the gas phase area from where it was taken, following the principle of proximity. If the properties of the media are similar and there are no process-related interference or negative effects, several pumps can share the same return area. Still, caution is required
Should it be gas that comes back? What is the relationship between the return pressure and the outlet pressure?
R/RW type shielded pumps require an anti-circulation pipeline, whose function is: A) The anti-circulation pipeline allows the liquid used for lubricating the bearings and cooling the motor to be returned promptly to the gas phase area of the tank, thereby preventing vaporization from occurring inside the motor chamber； B) During pump startup, even if a small amount of gas is present in the motor chamber, it can be expelled through the reverse circulation tube, enabling self-ventilation and preventing failure to start due to gas accumulation in the motor chamber ； C) Especially after the pump has been stopped for a while during operation, the motor remains hot; any fluid present within the motor chamber will turn into gas, and this gas can be discharged through the reverse circulation pipe when the pump is started again, ensuring smooth operation ；
What is returned is a liquid, but there is gas present; it looks no different from the flow back from centrifugal pumps – it’s still a liquid
This post was last edited by wsts00100 on 2023-1-6 at 13:20. BTY: I’m not trying to post ads; I’m just giving you the advice provided by the manufacturer.
These are mainly pumps for liquefied hydrocarbons and easily liquefiable gases; booster wheel canned pumps (Dalian Empire) can be used. We chose the Empire canned pump because the pipeline leading back to the tank with a tail section is too long, which makes it inconvenient