Pump vibration increases
Thread Content
One of our plants’ vertical tubular belt pumps is two-stage and over four meters long; the sections are connected by support tubes. Due to abnormal noises that were reported earlier, both the pump shaft and the graphite sleeves have become worn out. A new shaft and graphite sleeve have been installed. Due to a measurement error by the manufacturer, the thread pitch at the end of the pump shaft was mistakenly set from 10 inches per tooth to 1.75 millimeters per tooth; a gear (used to connect the pump to the motor) was then manufactured at a processing factory. After reinstalling it, the vibration increased and the pump can no longer be used. The concentricity of the motor and pump was measured several times with no issues, and the base was also adjusted, but it still doesn’t work. I would like to ask which expert can give me some guidance
Please share the data from the maintenance record.
The concentricity is around 5 degrees; normal vibration levels are 1.3 mm/s and 1.5 mm/s. After reinstallation, the vibration levels are 5.3 mm/s and 7.2 mm/s. Outlet pressure: 3.8 MPa. Pressure is stable, sound is normal; the measurement point is at the connection between the motor and the pump
The shaft is a newly manufactured one, over 4 meters long; it’s not possible to measure its verticality
How is the coupling sized, and what is the position of the rotor after it is connected?
After replacing the backrest wheel, the dynamic balance of the rotor was disrupted; it is necessary to perform low-speed dynamic balancing on the entire rotor.
On the outside of the mechanical seal, the gauge housing is located on the motor’s rear wheel; it is detached and not secured by bearings (there is only a gap between the graphite sleeve and the shaft, which allows for self-lubrication), and the shaft can move around. During installation, the shaft’s play was measured, and the intermediate value was obtained.
What’s an issue now is that the balance has been disrupted; a basic dynamic balancing procedure cannot be carried out. I would like to know what method can be used to address this. If nothing else works, could we simply use the original parts for welding and then re-machine the threads? Is that a viable option?
For vertical pumps, ensure that the clearance between the shaft and bearings is not excessive. The shaft needs to be run out. Even if it’s vertical, it still needs to be vibrated. The pulsation value shall meet the requirements of centrifugal pumps. The impeller needs to be statically balanced. If high precision is required, it would be better to perform balancing on a mandrel dynamic balancer.
Remove the motor and check its levelness. During operation, the motor housing needs to be measured, as well as the pump body; it is necessary to compare which one has a greater value, and both the amplitude and intensity need to be measured. I don’t know if you checked the pump cover area at that time. What was the bearing clearance at that time, and how was the turning of the shaft? Do not rule out the possibility that the motor is the source of vibration.