Pump selection
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Our factory uses a negative pressure distillation process: the product is taken from the top of the tower while the residues are removed from the bottom; the negative pressure inside the tower is around 100 millimeters of mercury； The liquid waste discharged is highly alkaline, containing gums and heavy metals; its viscosity is similar to that of diesel, and its temperature is around 190 degrees. In the past, magnetic self-priming centrifugal pumps were used to remove this waste, but it was often impossible to pump it out. Even when it was possible to do so, the outlet pressure could only reach around 0.08 MPa, and the outlet valve could only be opened slightly – opening it further would cause the flow to stop ； Recently, it seems that the magnetic force has weakened, and it’s not possible to completely drain the pressure under negative conditions; therefore, we have to take the risk of releasing the pressure to positive levels in order to drain it. We’re seeking expert advice on selecting a pump that can operate stably. Given that our factory is relatively small, it would be ideal if the pump were also cost-effective.
A self-priming pump needs to be filled with liquid every time it is used for the first time. According to your description, the liquid inside the pump cannot be emptied; if it needs to be emptied, the pump must be filled with liquid again. (Maybe that’s why you can’t achieve negative pressure.) The total value of the negative pressure and the outlet pressure you selected is less than 0.1 MPa; it’s possible that the pump chosen is not powerful enough (the viscosity and specific gravity of the liquid need to be taken into account). The fact that the outlet can only be opened a little bit is likely due to this reason as well. Then your temperature is 190 degrees; if a magnetic pump uses samarium-cobalt magnets at this temperature (if neodymium magnets are used, demagnetization is likely to occur).
Talk about inlet pressure, flow rate, head, and effective net positive suction head.
I understand: the material should contain a certain amount of solids, and over time the solid content in the small tank in front of the self-priming magnetic pump increases, which prevents discharge. Unscrew the small tank and connect it directly to the pump inlet to see how it works