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, the system has experienced issues such as material blockage, which significantly affects production efficiency. This paper presents an analysis of the causes behind these blockages and offers practical solutions to resolve them. 1. **Roots Blower Failure** 1.1 **Improper Pressure Setting on the Outlet Relief Valve** During the initial trial phase, as the mill feed rate increased, the pneumatic lift pump began to experience material blockage. The current of the Roots blower was around 65%, which is within the normal range, but the outlet safety valve kept releasing air. However, the pressure gauge readings did not reach the set pressure of 80kPa for the safety valve. After adjusting the pressure setting on the relief valve, the issue of material blockage was resolved. 1.2 **Belt Slipping or Burning** When the V-belt became worn or aged, and the tension was not properly adjusted, it often led to the belt slipping or burning. For example, the control room screen showed the current of one Roots blower dropping from about 70% to the no-load level of 40%, while the other two blowers' currents increased from 70% to 80%. Due to a lack of attention to this alarm, the backup blower was not switched in time, resulting in material blockage. On-site inspection revealed that all three Roots blowers had their outlet safety valves releasing air. The V-belt on the first blower had either fallen off or burned out, causing the motor to run idle. Switching to the backup blower fixed the problem. 1.3 **Failure of the Check Valve Spool or Wear of the Disc** The check valve at the outlet of the Roots blower is designed to prevent backflow of pressurized air into the rotor chamber after the fan stops. If the valve disc wears out, air can flow back through the gap, damaging the spool over time. This failure leads to the following symptoms: The control room display shows the current of all three Roots blowers dropping instantly from 70% to 40%, the safety valves do not release, but the pneumatic lift pump is blocked. Air flows from the faulty blower through the exhaust pipe and into the suction line. When the faulty blower is stopped, the shut-off valve closes, and the other two blowers’ currents jump to 80%, with the safety valves releasing air. 2. **Damaged Canvas Layer in the Pneumatic Lift Pump** If the canvas layer inside the pneumatic lift pump is damaged, the raw material cannot be properly vaporized, reducing the pump's conveying capacity. When the feeding amount exceeds the pump’s capacity, blockage occurs. The Roots blowers show a current of about 80%, and the safety valves are deflating. Solution: There is no need to stop the system immediately; the canvas can usually be replaced during scheduled maintenance. On-site, there is no need to open the pump manhole. Instead, the top bag dust removal fan inlet valve can be opened, and all three Roots blowers can be operated to pump the material out of the system. 3. **Wet and Caking Material Entering the System** Material blockage caused by moisture is common, especially when wet material from the humidification tower enters the pneumatic lift pump via the screw conveyor. This material cannot be fully vaporized and causes blockage. The control room shows the Roots blower currents at around 40% (no-load), the safety valves are not releasing, but the feed chute is overflowing, and the pump body sounds dull when tapped. Solution: Stop the raw mill system, open the pump manhole, manually remove the material, clean the canvas, and then restart the system.

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FCX Metal Structure Co., Ltd. , https://www.fcxmetal.com