Analysis of Common Causes of Slurry Pump Failures
Because slurry pumps are among the most widely used general-purpose mechanical equipment and are applied across various industries, the operating conditions differ among these industries. Therefore, equipment failures under different application conditions also vary. However, most failures are directly related to the initial equipment selection and the harsh operating conditions after use. The most common failures in alumina production are discharge blockage and severe vibration issues.
1. No discharge or poor discharge during operation
Slurry pumps failing to discharge or having poor discharge during operation is a fault encountered in almost all industries using slurry pumps. When a slurry pump fails to discharge after initial commissioning or major overhaul, it is related to the pump selection or replacement of spare parts, mostly caused by a low feed liquid level or incorrect rotation direction after pump operation.
The main reasons for sudden no discharge faults in slurry pumps under normal working conditions are as follows:
(1) Blockage of the impeller passage or pump inlet/outlet. A large part of the sudden no discharge fault in slurry pumps under normal working conditions is caused by blockage of the impeller passages or the pump's inlet/outlet pipelines. Since the slurry conveyed by the pump contains many solid particles, some of which are large in diameter, and the slurry generally has strong coagulation properties that easily form crusts, as well as the mixing of other flexible foreign objects, all these factors affect the normal entry of slurry into the pump chamber. Blockage of the impeller or inlet/outlet pipelines also makes it difficult for the slurry to receive the energy transmitted by the impeller. After this fault occurs, abnormal noises often accompany the pump chamber, and the motor current shows a significant downward trend.
(2) Cavitation occurrence. Cavitation is related to blockage of the slurry pump's impeller or pump inlet. Since blockage of the impeller or inlet itself affects the pump's discharge, cavitation not only further worsens the poor discharge but also generates noise and severe vibration, causing a decline in the overall performance of the slurry pump. In severe cases, it can interrupt the pump's discharge, and the motor current will show obvious fluctuations.
(3) Severe wear of flow-through parts. The wear of the main flow-through parts of the slurry pump is a gradual process, and as these parts wear down, the pump's performance gradually declines. The poor discharge caused by wear of flow-through parts has a long cyclical nature. In most cases, the pump runs very smoothly, and the motor current remains very low but stable.
2. Severe vibration of the slurry pump
Vibration is an inevitable phenomenon during equipment operation. According to the severity of vibration, it can be classified into different levels. Vibration within the acceptable level range is considered normal. If the equipment exceeds the normal vibration level, it will directly affect the stable operation of the equipment.
There are many causes of severe vibration in slurry pumps, generally including the following aspects:
(1) Impeller unbalance. The slurry pump impeller is dynamically balanced and aligned before leaving the factory, with relatively uniform mass distribution. However, after long-term operation, some wear or crust formation occurs, which to some extent causes unbalance in the rotating parts of the slurry pump. This unbalance after operation leads to severe unbalanced rotational forces, causing slurry pump vibration.
(2) Loose fixing bolts. The slurry pump is connected to the foundation by multiple anchor bolts, and bolts also maintain the stability of various components. Due to the presence of vibration, long-term operation of the slurry pump gradually causes these fastening bolts to loosen. This results in increased vibration because the pump loses the restraint of the fixing bolts. Meanwhile, the vibration and further loosening of bolts and component wear form a vicious cycle.
(3) Insufficient bearing lubrication or substandard lubricant grade. Good lubrication not only reduces component wear but also the oil film formed by lubricant between two parts absorbs a significant portion of vibration. During high-speed rotation of the slurry pump, the lubricant forms a sufficient oil film between the rolling elements of the bearing, reducing vibration. If lubrication is insufficient or the lubricant grade is substandard with inadequate viscosity, an effective oil film cannot form between bearings, or the oil film breaks prematurely, causing severe vibration and serious bearing wear.
Shaft seal leakage is the most common fault in slurry pumps, especially in the petrochemical industry, where over 80% of pump failures are due to shaft seal leakage. Therefore, the management of shaft seal leakage determines the pump's utilization rate and maintenance cost. Among shaft seal leakage faults, over 65% are caused by poor sealing of the sealing end face due to scaling of compression springs and cooling water. Thus, preventing shaft seal leakage focuses on softening the cooling water to reduce scaling speed.
