Centrifugal pumps do not generate pressure in a vacuum environment
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Submersible centrifugal pumps can generate pressure normally in an atmospheric environment, but when the container is evacuated and the pump is started, the pressure at the pump outlet becomes negative. What is causing this? (The material is an organic solvent; other materials could be used to generate pressure before). Is it because NPSHr > NPSHa? Or for other reasons?
The operating conditions shall be in accordance with those indicated on the label of the control pump, and it is mandatory to meet these operating conditions. For reference.
In this case, a negative-pressure centrifugal pump is required, with vacuum before the pump and positive pressure after it.
There is a branch in the pump outlet pipe that leads back to the container; it remains open when the pump is running. Therefore, under vacuum conditions, the pressure at the inlet and outlet of the pump is the same. Previously, it was possible to build pressure normally, but recently it takes some effort to do so.