Maintenance and Management of High-Temperature Gear Pumps

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High-temperature gear pumps are essential equipment for transporting, pressurizing, and metering polyester melt. High-temperature gear pumps are more compact in structure, operate more reliably, consume less energy, and have higher volumetric efficiency compared to other types of melt pumps. They exert less shear force on the melt, maintain a stable flow rate under high viscosity and pressure conditions, and exhibit no fluctuations in outlet pressure. The unique advantages of this pump, along with its critical role in the production process, make it indispensable in polyester manufacturing. Nevertheless, if the pump is not operated properly and is not managed adequately, it will not only fail to perform effectively but may even suffer sudden damage. I. Structure and Working Principle A complete gear pump consists of a motor, a reducer, a coupling, and a pump head. The pump head is made up of a pump casing, front and rear side covers, a gear shaft, sliding bearings, and shaft seals. High-temperature gear pumps belong to positive-displacement pumps; they transport the melt by utilizing the changes in working volume that occur as a result of the meshing between the driving and driven gears during operation. The working volume is composed of the pump body, the tooth grooves of the gears, and the bearings that serve as side plates. When the gears rotate in the direction shown in Figure 1, the melt enters the tooth grooves of the two gears in the suction chamber. As the gears turn, the melt is carried from both sides into the discharge chamber. The re-engagement of the gears forces the melt in the tooth grooves to be extruded out of the discharge chamber and pushed into the outlet pipe. As long as the pump shaft rotates, the gears push the melt toward the outlet side; therefore, a very high pressure can be achieved at the pump outlet, while the flow rate is essentially independent of the discharge pressure. II. Operation Management 1. Routine Maintenance (l) The disassembly and cleaning of pumps, as well as operations related to raising or lowering temperature and starting or stopping the pumps, must all be carried out in strict accordance with established procedures to avoid unnecessary losses. (2) Attention should be paid to maintaining stable inlet pressure of the booster pump, so as to ensure its stable volumetric efficiency, which is beneficial for the proper operation of the pump itself and the stability of the spinning quality downstream. (3) For stuffing shaft seal pumps with negative pressure at the population, the pressure in the stuffing box should be maintained above the external atmospheric pressure. When the back pressure decreases, the pressure in the stuffing box should be adjusted promptly; otherwise, air will be drawn into the pump, causing the cast strip to break and affecting granulation, which in turn leads to discharge from the granulator. (4) The temperature of the heat transfer medium jacket should be checked regularly, and the temperature of the heat transfer medium in the main body and the front and rear covers must remain consistent. (5) Each time the output increases, it is necessary to record the current output, rotation speed, inlet and outlet pressures, as well as the current value. By comparing these data before and after, a thorough analysis should be conducted in order to detect any abnormalities as early as possible and take timely action. 2. Common faults and countermeasures are as follows: (1) Fault symptom: The pump cannot discharge fluid. Cause of the fault: a. Opposite rotation direction ； b. The intake or exhaust valve is closed ； c. No material at the inlet or insufficient pressure ； d. Excessively high viscosity prevents the pump from gripping the material. Solution: a. Verify the rotation direction ； b. Verify whether the valve is closed ； c. Check the valves and pressure gauge ； d. Check the liquid viscosity to see whether a flow rate proportional to the rotation speed occurs at low speeds; if there is a flow rate, then the inflow is insufficient. (2) Fault symptom: Insufficient pump flow rate. Cause of the fault: a. The suction or discharge valve is closed ； b. Low inlet pressure ； c. Clogged outlet pipeline ； d. Packing box leakage ； e. Low rotation speed. Countermeasure: a. Verify whether the valve is closed ； b. Check whether the valve is open ； c. Verify whether the discharge volume is normal ； d. Tighten ； When a large-scale leakage affects production, operations should be stopped and the equipment disassembled for inspection ； e. Check the actual rotational speed of the pump shaft ； (3) Fault symptom: Abnormal sound. Cause of fault: a. Large eccentricity of the coupling or poor lubrication; b. Motor failure ； c、Abnormality in the reducer ； d、Poor installation at the shaft seal ； e. Shaft deformation or wear: Countermeasures: a. Align or fill with lubricant ； b. Check the motor ； c. Check the bearings and gears ； d. Check the shaft seal ； e. Parking and disassembly inspection (4) Fault symptom: Excessive current. Cause of the fault: a. Excessively high outlet pressure ； b、Excessively high melt viscosity ； c、Poor shaft seal assembly ； d. Wear of the shaft or bearings ； e. Motor failure Countermeasures: a. Check downstream equipment and pipelines ； b. Test viscosity ； c. Check the shaft seal and adjust it as appropriate ； d. After parking, check by manually turning the shaft to see if it is too heavy ； e. Check the motor (5) Fault symptoms: The pump stops suddenly. Cause of the fault: a. Power outage ； b. Motor overload protection ； c. Damaged coupling ； d. Excessive outlet pressure, interlock reaction ； e. Abnormal seizure inside the pump ； f. Adhesion and jamming of the shaft and bearing. Solution: a. Check the power supply ； b. Check the motor ； c. Open the safety cover and rotate the shaft for inspection ； d. Check the instrument interlock system ； e. After parking, confirm by rotating the crankshaft in both forward and reverse directions ； f. Crankshaft rotation verification. Note: The above fault symptoms and corresponding countermeasures are in a one-to-one relationship. III. Measures to improve operational life: 1. Since the pump operates at high temperatures, hinge supports should be installed on the piping during installation in a cold state, to prevent the piping from shifting as the temperature rises. 2. The coupling must be aligned thermally after the pump body has warmed up, in order to avoid additional torque being generated during operation. 3. An interlock shutdown alarm should be installed at the pump outlet pressure monitoring point; otherwise, if the discharge pipeline is blocked, it can easily cause damage to the pump. 4. When starting the pump, do not increase the speed recklessly when no pressure has been established at the outlet, in order to prevent premature damage to the shaft or bearings. 5. When cleaning the pipette, do not use a pump to deliver the cleaning solution; instead, remove the internal components and reinstall them after the cleaning is complete, to prevent foreign objects from entering the pump. 6. The temperature of the heat medium jacket in the pump body can be slightly lower than that of the heat media in the front and rear jackets.