The problem of excessive vibration in centrifugal pumps
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Hey everyone: Currently, my installation is experiencing the same vibration issues under different operating conditions in two pumps. 1. One 600m3 circulation pump, of horizontal type with a bearing housing (single support); the motor has a power of 110kw. During individual testing, the vibration level was very low, around 1.3 mm/S or less. However, once the pump was connected, the horizontal vibration on the side close to the coupling increased to 6.5 mm/S, while the vertical vibration was 3.4 mm/S and the axial vibration was 3.2 mm/S. The pump was aligned four times, a new coupling was installed, new front and rear bearings were used, and the impeller was removed for inspection and cleaning； 2. A 150m3 salt water pump, with exactly the same fault as the one mentioned above. The vibration parameters of the salt water pump are shown in the image below
What type of coupling is it? Could I see the data related to alignment? Is there any corrosion or thinning in the impeller, and should we check whether there are any issues with dynamic balance?
The coupling of the water pump has been removed; the salt water pump uses a diaphragm coupling, and the alignment is within 5 threads, which ensures no problems. The impeller is corroded, but it’s due to normal scale and corrosion. Dynamic balancing was not performed – only the roundness of the shaft was checked
Has the pipe stress been checked? It would be best to be able to measure the spectrum, as it helps in identifying problems. If dynamic balancing is not possible, static balancing can be done instead
For diaphragm couplings, what is the axial clearance? Dismantle the coupling and check the following: 1. Whether there is an interference fit between the inner diameter of the elastic ring and the outer diameter of the coupling bolts; 2. Whether the gap between the outer diameter of the elastic ring and the coupling hole is between 0.5 mm and 1 mm; 3. Whether the taper fit between the coupling bolts and the coupling hole is tight enough. 4. When tightening the coupling bolts, are there washers under the nuts? Is it ensured that the nuts, washers, bolts, and coupling are tightened firmly? 5 Two-coupling wheel axial clearance: 2 to 6 mm
Check whether the coupling is deformed by using a dial indicator to measure the flatness of its end face
It works fine after being used; new wheels have also been installed, and there’s no change in the vibration characteristics or level
Single diaphragm? Change the single diaphragm to something else
If there is corrosion, impeller and rotor-related spare parts are required. You might as well order another set of rotors, replace them and give it another try to see what the problem is. It is mainly to verify the dynamic balance of the rotor. Also, check that the opening spacing of the couplings is not too tight, as well as the foundation bolts and bearings. For reference.