1、 Overview of faulty equipment

Vertical pipeline pump motor drive length is 1879.6 mm, shaft diameter is 88.9 mm, and wall thickness is 2.4 mm. The number of blades of the impeller is 2. The vertical pump shaft has broken for many times, and the broken part is close to the impeller compression nut. The fault phenomenon is that the vibration is large at the beginning (large at 3V and 4V), and the impeller compression nut is loose. Then use epoxy to stick the impeller compression nut, which can effectively prevent the nut from loosening. However, many pumps later suffered catastrophic damage from impeller shaft fracture.

Decide to monitor and analyze: measure vibration; Assess the severity of vibration; Diagnose potential faults; Propose effective troubleshooting measures.

2、 Vibration measurement data and fault analysis

1. Vibration measurement shows that the vibration of 3V and 4V measuring points is large. In the spectrum of 3V measuring point, the amplitude of 2 * RPM frequency 3570rpm component reaches 16.51mm/s peak, while the amplitude of 1 * RPM frequency component is only 4.60mm/s peak. Note: The number of blades of the impeller is 2, and the blade passing frequency BPF=2 * RPM.

2. Test results of hammering method: use hammering method to test the natural frequency of motor, shaft and pump. The natural frequency test spectrum of 4V measuring point shows that the dominant natural frequency is 3780rpm, which is only 210rpm or 5.9% different from the vibration frequency component of 3570rpm=2 * RPM=BPF of the spectrum measured in operation. In addition, there is the natural frequency of the 2009 rpm shaft guard. Since the natural vibration frequency of 3780rpm is too close to the passing frequency of the blade of the pump impeller or the double frequency of the pump speed of 3570rpm, the pump system resonance is easily aroused. Therefore, the supporting stiffness of the reinforced pump system used in the test changes the natural frequency of the system ("frequency modulation") to avoid resonance.

3、 Failure treatment and effect reinforcement scheme

The measured vibration of the pump system before and after reinforcement shows that the natural vibration frequency after reinforcement is increased to 3960 rpm, which is 180 rpm or 4.8% higher, so that it is effectively staggered from the BPF=2 * RPM excitation frequency to avoid resonance. The total vibration of 3V measuring point decreased from 18.14mm/s peak to 5.99mm/s peak, with a reduction of 67%. The amplitude of the 3570rpm component of the 2 * RPM frequency decreased from 16.51mm/s peak to 4.98mm/s peak, with a reduction of 70%.