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**Abstract:**
Based on the vibration analysis of large-scale deep well pumps and various potential causes of vibration, this paper proposes a practical field method for identifying issues related to motors and pumps. Panzhihua Iron and Steel, located in the upper reaches of the Jinsha River, has constructed a large deep-well pump station. The facility consists of two 18-meter diameter deep wells, each 31 meters deep, with an upper plant structure. The river water is directed into the deep well through four Dg1200 pipes. The upper section of the well houses 20 sets of 30JD-19x3 sand control deep well pumps mounted on reinforced concrete frame beams with a cross-section of 1450 mm × 410 mm. After prolonged installation and maintenance, we conducted detailed investigations into the root causes of vibration.
First, the technical specifications of the deep well pump are outlined: Model 30JD-19x3, three impellers, flow rate of 1450 m³/h, drive shaft length of 24.94 m, shaft diameter of 80 mm, made of 40Cr, speed of 985 rpm, thrust tile oil temperature below 50°C, cooling water pressure of 0.8 MPa, ascending pipe inner diameter of 500 mm, head of 80 m, rubber bearing lubrication medium, single motor weight of 14 T, type JKL15-6 vertical motor, rated power of 500 kW, voltage of 6000 V, current of 60 A, motor rotor moment of inertia of 58 kg·m², motor weight of 4 T, and allowable vertical and horizontal amplitude of less than 0.10 mm. The water quality must not exceed 0.1% sediment, with particle size no larger than 0.2 mm, and the first impeller should be submerged at least 1 meter below the water level. During flood seasons in July and August, the water turbidity from the deep well pumps can reach up to 20%.
Second, the process of fault diagnosis for vibration is discussed. When vibration occurs during operation, the coupling between the motor and pump should be disconnected first to determine whether the source is the pump or motor. It is also essential to check if the motor base and pump connection bolts are tightened and if the installation level is within tolerance.
1. **Motor Vibration Sources and Diagnosis**
(1) Rotor speed close to critical speed: If the motor's rotational speed is near its critical speed, resonance may occur, especially when the pump frequency aligns with it. Motor speeds should ideally be at least 25% below or 40% above the critical speed. Additionally, the rotor’s mass distribution along the axis must be considered, as higher-order critical speeds (e.g., second and third order) can significantly affect performance.
(2) Rotor imbalance: This is one of the most common causes of vibration. For example, motors #17 and #19 showed vibration velocities of 9.8–10 mm/s, exceeding the ISO 2372 standard for Class III machinery (less than 4.5 mm/s). By balancing the rotor using parallel rails and adjusting weights, the vibration was reduced to 0.05 mm and 2.1 mm/s, respectively.
(3) Bearing wear and misalignment: After long-term use, checks should be performed for excessive bearing clearance, loose mounting screws, bent or worn shafts, and uneven air gaps. Stator ring gaps should not exceed 10%. Even if the motor is within acceptable amplitude limits, system-wide factors may cause vibration under load.
2. **Pump Body Vibration and Diagnosis**
(1) Installation and assembly errors: Improper alignment of the pump body, thrust plate, and vertical pipe can lead to vibration. The total length of the pumping pipe and pump head (excluding the filter) is 26 m, all suspended. Vertical deviation of the pipe must be controlled within ±2 mm, and the horizontal error should be less than 0.05/1000 mm. Impeller static balance tolerances must not exceed 10 g, and proper clearance should be maintained.
(2) Shaft whirl: Also known as "rejection turn," this self-excited vibration occurs due to insufficient lubrication, misalignment, or improper clearance. Long deep well pump shafts (24.94 m) are particularly prone to this issue. Inadequate lubrication or blockages can cause the shaft to rotate in the opposite direction, leading to bearing damage.
(3) Overload-induced vibration: Thrust pads made of tin-based Babbitt alloy can fail if overloaded. During startup, if valves are not fully open, it can result in sudden pressure surges and severe vibration. For example, pump #17 experienced such issues due to valve blockage.
(4) Outlet turbulence: Turbulent flow at the pump outlet, caused by valves and short tubes, creates pulsations that transmit energy to the pump body. When the turbulence frequency matches the system’s natural frequency, resonance occurs. Proper valve positioning, tube length, and additional bearings can reduce this effect.
(5) Torsional vibration: Due to the long shaft and flexible coupling, torsional vibrations from different angular frequencies can interact. This affects the thrust pad, so improving oil viscosity (from 68# to 100#) helps maintain dynamic pressure lubrication.
(6) Interference between pumps on the same beam: Pumps and motors installed on the same reinforced concrete beam form a two-degree-of-freedom system. If one motor vibrates excessively, it can affect the neighboring pump, even during idle runs. This interaction requires careful monitoring.
In conclusion, systematic vibration analysis and regular maintenance are essential for ensuring the stable operation of large deep well pumps. By identifying and addressing these key sources of vibration, efficiency and reliability can be significantly improved.