**Abstract:** Based on the vibration analysis of large-scale deep well pumps and the various factors that may lead to vibration, this paper proposes a practical method for identifying motor and pump issues in the field. In Panzhihua Iron and Steel, located upstream of the Jinsha River, a large deep-well pump station has been constructed. The station consists of two 18-meter diameter wells, extending 31 meters deep, with an upper plant configuration. Water from the Jinsha River, with a flow rate of 4,000 m³/h through pipes of DN1200, is pumped into the deep wells. The upper section of the well is supported by a reinforced concrete framework measuring 1,450 mm × 410 mm, where 30JD-19x3 type sand deep well pumps are installed. After long-term operation and maintenance, we conducted detailed investigations into the causes of vibration. **Technical Parameters of the Deep Well Pump** - Model: 30JD-19x3 (three impellers) - Flow Rate: 1,450 m³/h - Shaft Length: 24.94 m, consisting of 9 shafts - Pump Shaft Diameter: 80 mm - Shaft Material: 40Cr - Speed: 985 rpm - Thrust Oil Temperature: < 50°C - Cooling Water Pressure: 0.8 MPa - Pipe Diameter: 500 mm - Head: 80 m - Bearing Lubrication Medium: Water - Motor Weight (without): 14 tons - Motor Model: JKL15-6 - Rated Power: 500 kW - Rated Voltage: 6,000 V - Rated Current: 60 A - Motor Rotor Moment of Inertia: 58 kg·m² - Motor Weight: 4 tons - Allowable Amplitude (Vertical/Horizontal): < 0.10 mm The water quality requirements for the pump specify that sediment content should not exceed 0.1% and particle size must be less than 0.2 mm. The first impeller should be submerged at least 1 meter below the water level. During flood season (July–August), the sediment concentration in the Jinsha River can reach nearly 20%, which poses significant challenges for the system. **Vibration Fault Diagnosis** During operation, if the pump or motor exhibits vibration, the first step is to disconnect the coupling to determine whether the vibration originates from the pump or the motor. It’s also important to check the tightness of the vertical motor base and pump connection bolts, as well as ensure proper installation levels. **Motor Vibration Sources and Analysis** 1. **Critical Speed Proximity**: If the motor rotor speed is close to its critical speed, resonance could occur. Calculating the torsional stiffness and frequency helps identify potential resonance. The motor rotor speed should ideally be at least 25% below or 40% above the critical speed. Higher-order critical speeds should also be considered during analysis. 2. **Rotor Imbalance**: This is the most common cause of vibration. For example, motors #17 and #19 showed vibration velocities of 9.8–10 mm/s, far exceeding the ISO 2372 standard for Class III machinery (≤4.5 mm/s). By using a simple balancing setup with rails and adjusting the weight distribution, the amplitude was reduced to 0.05 mm, and the velocity dropped to around 2.1 mm/s. 3. **Bearing and Mechanical Issues**: Over time, excessive bearing clearance, loose mounting screws, or worn shafts can contribute to vibration. Additionally, uneven air gaps between the stator and rotor should be checked, with a maximum gap of 10%. **Pump Vibration Causes and Diagnosis** 1. **Installation Deviations**: Misalignment in the pump body, thrust level, or vertical pipe can cause severe vibrations. The vertical deviation of the pumping pipe should be within ±2 mm, and the horizontal error should be <0.05/1000 mm. 2. **Shaft Whirl (Rejection Turn)**: This self-excited vibration occurs when the shaft rotates in a direction opposite to the bearing motion, often due to insufficient lubrication. Long deep well pump shafts with rubber bearings (gap of 0.20–0.30 mm) are especially prone to this issue. 3. **Overload Conditions**: When the pump starts, if valves are not fully open or blocked by sediment, it can cause high pressure and damage the thrust pad. 4. **Outlet Turbulence**: Turbulent flow at the outlet, caused by valves and short pipes, can induce pulsations that lead to vibration. Ensuring full valve opening and proper pipe length can reduce this effect. 5. **Torsional Vibration**: With a 24.94 m long shaft, torsional vibrations from different angular frequencies can interact. Using higher viscosity oil (e.g., changing from 68# to 100#) helps maintain the lubrication film and reduce wear. 6. **Interference Between Pumps**: When multiple pumps are mounted on the same beam, their vibrations can interfere. One pump’s severe vibration can affect another, even without load, making it crucial to monitor closely. This comprehensive approach ensures early detection and resolution of vibration issues, improving the reliability and efficiency of large-scale deep well pump systems.

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