Operation of the centrifugal pump in the unit—what to do if the pump gets evacuated?

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In actual production operations, it is common for centrifugal pumps to experience vacuum conditions. What should be done once a centrifugal pump reaches a vacuum state? Below is a summary of the pumping-out phenomenon in centrifugal pumps, its causes, and remedial measures, in the hope that it will be useful for your work. Dangers of pump evacuation: 1) The pump body vibrates severely, causing the moving and stationary rings of the mechanical seal to collide intermittently, which leads to leaks; in severe cases, the mechanical seal structure fails ； 2) The compression of the stationary and rotating rings in a mechanical seal is the sum of the medium pressure and the pre-tightening force of the spring; when evacuation occurs, the medium pressure disappears, the contact pressure between the stationary and rotating rings decreases, and the seal fails ； 3) After the pump is evacuated, the rotating and stationary ring surfaces of the mechanical seal, which rely on a self-flushing mechanism (that is, flushing with the pumped fluid), lose cooling and lubrication, resulting in dry friction and failure of the mechanical seal. I. Phenomenon of pump evacuation 1. Decrease in motor current. 2. Significant pressure fluctuations. 3. Abnormal fluctuations in traffic volume. 4. Emiting noise and abnormal sounds. 5. The pump body vibrates. 6. The pump cylinder temperature rises. 7. Causes damage to the impeller. 8. Cause traffic interruption. II. Reasons for pump evacuation 1. Air leakage at the inlet of the centrifugal pump. 2. Blockage has occurred at the inlet of the centrifugal pump. 3. The pressure at the inlet of the centrifugal pump is insufficient. 4. The temperature of the medium at the inlet of the centrifugal pump is too high, resulting in excessive saturated steam. 5. The inlet valve of the centrifugal pump is not open or the valve core has fallen off. 6. The outlet opening of the centrifugal pump is too large (too small). 7. The seal oil of the centrifugal pump contains water. 8. The liquid level in the centrifugal pump tower or container is low or absent. 9. The impeller or internal wear ring of the centrifugal pump is severely worn. 10. The motor of the centrifugal pump is running in reverse. III. Methods for dealing with pump evacuation 1. If there is air leakage at the inlet, the pump should be stopped to inspect the leaking inlet pipelines and flanges of the centrifugal pump. 2. If the inlet is blocked, the pump should be stopped to inspect the leaky inlet piping and impeller of the centrifugal pump; after purging, repairs should be carried out. 3. If the inlet pressure is insufficient, the back pressure at the liquid level should be increased. 4. If the temperature of the inlet medium is too high, the medium temperature should be reduced, and the steam inside the centrifugal pump should be completely vented. 5. If the inlet valve is not open or the valve core has fallen off, the valve should be opened or a new pump should be installed before proceeding with maintenance. 6. If the outlet opening is too large (too small), the openings of various valves should be adjusted accordingly. 7. If the sealing oil contains water, the sealing oil tank should be dehydrated. 8. If the liquid level in the tower or container is low, the outlet valve of the centrifugal pump should be temporarily reduced or the pump should be shut down; operation can be resumed once the liquid level rises. 9. If the impeller or the internal grinding ring is worn, it should be replaced in a timely manner. 10. If the motor rotates in the reverse direction, the rotation direction should be adjusted promptly.