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With reference to the aforesaid objectives, the experiments have been performed in the following sequence: A centrifugal pump is run with 24 vanes brass impellers at various conditions (of impeller like non-defective, one vane removed, two vanes removed, three vanes removed). Vibration signal and motor current signals are recorded during operation/working condition and the data is analyzed by the PULSE analyzer.

 

Equipment used:

For performing the experiments, following instruments were used:

1. Accelerometer (PCB, 353B33)
2. Hall Effect Sensor (TektronixA621)
3. PULSE analyzer (Bruel & Kjaer)
4. Centrifugal pump coupled with induction motor (1 hp, 1450 RPM, 240 V, make- Crompton Greaves)

Impellers used in pump are made of brass; with external diameter 100 mm; width 10 mm; vane length 25 mm and number of vanes is 24.

 

 

Experimental Procedure

 

• Firstly, the water tank was filled with water to such a height so that the inlet pipe is just below the water level. Then the accelerometer was placed on the casing of the pump (as shown in fig 5) to measure the vibration and it is connected to analyzer through the data cable (B&K). Hall Effect Sensor (Tektronix A621) (as shown in fig 6) is connected to the analyzer through the data cable to measure the instantaneous motor current.

 

• The centrifugal pump was switched on and readings were taken under different working conditions of impeller like normal impeller (all vanes present), one vane broken impeller, two vanes broken impeller, three vanes broken impeller sequentially.The PULSE analyzer (as shown in fig 7) is used to analyze the vibration signal and motor current signal.

 

• Four no. of tests have been performed with different impeller conditions (two experiments have been done with each impeller condition for repetition). For each test, current and vibration signal data were collected. For each of the signal data the following were recorded

i. Recording data for 10 s

ii. Time domain data for 4 s for both current and vibration signal

iii. FFT Spectra upto1.6 kHz forboth current and vibration signal.

 

Using the recorded time history data, maximum, minimum, mean, RMS, standard deviation, variance, skewness, kurtosis, crest factor, form factor were calculated. FFT (both current and vibration) analysis is done for getting rotating speed (RPS) of pump, Vane pass frequency (VPF), Sidebands (SBs) around VPF and their respective amplitude (in dB).

 

Experiments

 

Four different sets of data have been obtained from each test. The result of each set is presented as follows. The following results were taken at the full flow rate of the pump.

The data, which was collected with the help of an accelerometer, were analyzed using PULSE and the vibration spectra were obtained.

The vane pass frequency (VPF) has been found from the vibration spectrum and compared with their corresponding amplitudes (in dB) and their sidebands, SBs (at VPF ± RPS) for different impellers. VPF is calculated by the product of RPS and number of vanes of the impeller. The VPF and its sidebands are shown on the respective vibration spectra for each test .

 

Attachment: Video of the pump operating at two different conditions

 

Test1:The first test with a Normal impeller.

Test2:The second test with a defective impeller (with one vane missing).

Test3:The third test with a defective impeller (with two vanes missing).

Test4:The fourth test with a defective impeller (with three vanes missing).