The first-line raw material storage and transportation system in our company utilizes a Φ1.6m × 8.5m pneumatic lift pump, which is powered by three Roots blowers. Over time, issues such as material blockage have been observed during the operation of the pneumatic lift pump. This paper aims to analyze the causes of these blockages and provide effective solutions. 1. **Roots Blower Failure** 1.1 **Low Pressure Setting on the Outlet Relief Valve** During early trial production, as the feed rate to the mill increased, material blockage began to occur. The current of the Roots blower was around 65%, which was within the normal range, but the outlet safety valve started to release air. However, the pressure gauge readings on-site did not reach the set pressure of 80kPa for the safety valve. After adjusting the pressure screw on the relief valve, the issue of material blockage was resolved. 1.2 **V-Belt Slipping or Burning** When the V-belt became worn or aged, and the tension was not properly adjusted, it could cause the belt to slip or burn. For example, the control room screen showed that the current of one Roots blower dropped from about 70% to the no-load level of 40%, while the other two blowers increased from 70% to 80%. Due to a lack of attention to the alarm, the standby blower was not switched in time, leading to material blockage in the pneumatic lift pump. On-site inspection revealed that the safety valves of all three Roots blowers had released air. The V-belt of the first blower had either slipped off or burned out, causing the motor to run idle. This resulted in an increase in current for the other two blowers. Switching to the backup blower resolved the problem. 1.3 **Failure of the Check Valve Spool and Wear of the Disc** The check valve at the outlet of the Roots blower is designed to prevent backflow of compressed air into the rotor chamber when the fan stops. The globe valve is controlled pneumatically, opening before the fan starts and closing after it stops to block the reverse flow. However, due to wear on the valve disc, some air could pass through the gap, causing the check valve spool to become dislodged over time. This led to material blockage, as shown by the following symptoms: The control room screen displayed the current of all three Roots blowers dropping instantly from about 70% to 40%, the no-load current. On-site, the pneumatic lift pump was blocked, but none of the safety valves were releasing air. Air from the faulty blower flowed through the exhaust pipe, into the rotor chamber, and then into the suction line. When the faulty blower was stopped and the shut-off valve closed, the current of the other two blowers jumped from 40% to 80%, and their safety valves released air. 2. **Damage to the Canvas Layer in the Pneumatic Lift Pump** If the canvas layer inside the pneumatic lift pump is damaged, the raw material fed into the pump may not be adequately vaporized, reducing its conveying capacity. If the feeding rate exceeds the pump's capacity, blockage occurs. At this point, the current of the three Roots blowers is typically around 80%, and the safety valves are releasing air. Solution: There is no need to stop immediately; the canvas can usually be replaced during scheduled downtime. On-site, it may not be necessary to open the pump’s manhole door to remove the material. Instead, the top bag dust removal fan’s inlet valve can be opened, and all three Roots blowers can be operated to pump the material out of the system. 3. **Incoming Wet or Caking Material** Material blockage caused by moisture is a common issue, especially when wet material from the humidification tower enters the pneumatic lift pump via the screw conveyor. This material cannot be fully vaporized, leading to blockage. In such cases, the control room shows the Roots blower currents at around 40%, which is the no-load level, and the safety valves do not release air. However, there may be visible material leakage at the feed chute, and tapping the pump body produces a dull sound. Solution: Stop the raw mill system, open the pump manhole, manually remove the material, clean the canvas layer, and restart the system.

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