Vibration Fault Analysis of Large Long-axis Deep-well Pumps III
Vibration Fault Analysis of Large-Scale Long-Axis Deep Well Pump (3)
This issue has been observed during daily operations, where the pump can run for a short period before causing damage to the rubber bearings.
(3) Vibration caused by overload. The thrust washer in the pump is made of tin-based Babbitt alloy, designed to handle a load of 18MPa (180kgf/cm²). However, at startup, the lubrication at the edge of the thrust pad may be insufficient. Additionally, the outlet of the pump is equipped with an electric butterfly valve and a manual gate valve. If the electric butterfly valve fails to open due to sediment buildup or if the manual valve is accidentally closed, the exhaust process is delayed, leading to excessive vibration in the pump body. This can quickly result in the burning of the thrust pad. The #17 pump is a typical example of this problem.
(4) Outlet turbulence-induced vibration. At the pump outlet, there are several components such as a short pipe, check valve, electric butterfly valve, manual valve, pressure gauge, and a water hammer eliminator. The turbulent flow of water creates irregular pulsations. Each valve introduces significant local resistance, causing changes in momentum and pressure. These fluctuations exert forces on the pipe walls and the pump, resulting in vibrations that can be observed through the pulsation of the pressure gauge. The fluctuating pressure and velocity fields in the turbulent flow continuously transfer energy to the pump body. When the main frequency of the turbulence matches the natural frequency of the deep well pump system, resonance occurs, leading to increased vibration. To mitigate this, valves should be fully opened, the short pipe should be of appropriate length, and additional bearings should be installed. After implementing these measures, the vibration levels were significantly reduced.
(5) Torsional vibration in the deep well pump. The long-axis deep well pump is connected to the motor via a flexible coupling, with a shaft length of 24.94 meters. During operation, vibrations from different angular frequencies overlap. The combination of two simple harmonic motions with different frequencies does not necessarily produce a harmonic vibration, resulting in a two-degree-of-freedom torsional vibration within the pump. This type of vibration is unavoidable and primarily affects the thrust pad. To ensure proper lubrication, the original 68# oil was replaced with 100# oil to increase viscosity. This helps maintain a stable dynamic pressure lubrication film on the thrust pad, preventing its failure.
(6) Vibration interaction between pumps mounted on the same beam. The deep well pumps and motors are installed on two reinforced concrete beams with a cross-section of 1450 mm x 410 mm. Each pump and motor has a mass of approximately 18 tons. When two adjacent pumps operate on the same beam, they form a two-degree-of-freedom vibration system. If one motor experiences severe vibration during no-load testing—when the elastic coupling is disconnected and the motor is idling—the amplitude of the other operating pump motor may rise to about 0.15mm. This situation is often overlooked but requires careful monitoring and attention.
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