Maintenance methods for rotary vane vacuum pumps

　

　　

　　 Maintenance methods for rotary vane vacuum pumps

　　1. First, you need to understand the type, characteristics, and current status of rotary vane vacuum pumps. Familiarize yourself with the usage requirements and define the repair objectives. Before starting the repair, make sure you have the necessary testing tools ready.

　　2. Identify the fault and confirm its nature. Accurate identification can save you a lot of trouble. Confirmation requires verification.

　　3. When troubleshooting, start with the simpler issues before tackling the more complex ones, and address easier problems before moving on to harder ones. Avoid disassembling components unless absolutely necessary. This approach helps minimize new damage caused by lack of specialized tools or improper handling, reduces the number of relocations, and shortens the run-in period. Generally speaking, spliced rotors are non-disassemblable; otherwise, their geometric tolerances will be compromised, rendering the rotor unusable.

　　4. For pumps that are toxic, harmful, or corrosive, users should first clean them and be informed of the necessary protective measures to ensure the health and safety of maintenance personnel.

　　5. Classification of Rotary Vane Vacuum Pump Faults

　　It is recommended to categorize faults into operational faults and performance faults.

　　Operational faults may include the pump failing to rotate, the pump temperature being too high, oil leakage, water leakage, and exceeding the maximum power rating.

　　Performance failures may include failure to meet or insufficient compliance with specifications for parameters such as ultimate pressure, ultimate total pressure, pumping efficiency, noise, oil injection, and gas ballast performance.

　　6. Examples of Fault Identification and Diagnosis

　　(1) The pump isn't turning. If the situation is unclear, do not start the pump yet, to avoid exacerbating the fault. Determine whether the pump can be turned by hand or not.

　　① The pump can be turned by hand but does not rotate. Possible causes include: coupling failure; belt slippage; incorrect motor wiring; motor damage; or no power supply.

　　② If the pump cannot be turned or is extremely difficult to turn, the reasons may include: the starting pump temperature being too low, resulting in excessively high viscosity of the pump oil; excessive backflow during pump shutdown due to design or manufacturing defects; excessive backflow caused by an excessively high oil level (due to overfilling, condensation of moisture vapor inside the pump, or condensation of water flowing back into the pump from the exhaust pipe); or the presence of foreign objects inside the pump (such as welding slag or oxides from the intake pipe, debris from pump components like vane springs, deformed vanes that have become jammed, or instances of mechanical seizure involving components such as copper sleeves, rotors, middle walls, pump covers, stators, and bearings).

　　(2) The pump temperature is too high. This refers to the highest oil temperature measured near the low-stage exhaust valve exceeding the value specified in the instruction manual. As the pump temperature rises, the viscosity of the pump oil drops significantly, and the saturation vapor pressure of the pump oil increases, leading to a higher ultimate vacuum and reduced pumping efficiency. It also accelerates the aging of rubber components. Thermal expansion narrows the operating clearances—particularly in the thickness direction of certain non-metallic vanes and in the clearance between the copper sleeve’s inner bore—thus compromising the reliability of pump operation. The causes of excessively high pump temperatures may include: excessively high ambient temperature around the pump, excessively high inlet gas temperature, failure of the inlet gas cooling system, prolonged continuous operation of the pump at an excessively high inlet pressure, insufficient cooling water supply for water-cooled pumps, poor design performance of the circulating water system, or failure of the temperature-controlled water flow regulating valve.

　　(3) Oil leakage can occur at various locations, including the shaft seals, sealing surfaces between the oil tank and pump components, drain plugs, oil level indicators, plugged oil ports, through-holes connecting the stator assembly to the support base, and the gas-boosting valve (e.g., 2X-8). Such leakage may be caused by aging of sealing elements, improper installation, damage or failure of seals, uneven surface conditions, presence of impurities, roughness, or porosity in cast parts. If oil flows back into the pump after it has been stopped, it may enter the gas-boosting valve; failing to close the gas-boosting valve properly could result in oil leakage.

　　When making rubber gaskets yourself, be sure to use oil-resistant rubber and follow the original design shape. If the sealing surface is too large, it won't compress tightly enough and will leak oil.

　　(4) Leaks can occur at pipe joints, the flat surfaces of water jacket covers, drain plug screws, drain valves, and other such areas. Additionally, leaks may be caused by water jackets being drilled through, casting defects, or freeze-induced cracks.

　　(5) Excessive high power. This can be caused by factors such as excessively high inlet pressure due to prolonged continuous operation, excessively high discharge pressure, foreign objects entering and causing seizure, excessively high pump temperature, too-small clearance between components like vanes, excessively high voltage, or excessive backflow of pump fluid into the pump itself—any of which can damage the motor. Therefore, it is advisable to avoid prolonged continuous operation near the maximum power setting whenever possible. If deposits accumulate on the surface, the unit should be periodically disassembled and cleaned.

　　(6) The maximum pressure does not meet the standard.

　　It can be caused by external leakage, internal leakage, blockage of oil passages, poor quality or contamination and deterioration of pump oil, the presence of condensable substances such as water vapor, distortion of instruments and meters, or abnormal pump operation.

　　When external leakage is significant, white vapor can be seen coming from the exhaust port. There will be numerous bubbles visible at the oil-level indicator, and you can feel exhaust pressure when placing your hand near the exhaust port. At the low-stage exhaust valve, the oil level will show a greater number of bubbles. Power output may also increase slightly. In such cases, the first thing to check is whether the gas ballast valve is properly closed. Since each newly manufactured pump has its ultimate pressure measured at the pump inlet, if external leakage occurs, you should carefully inspect the pump inlet as well as the pipelines, valves, and containers one by one. External leakage can also result from failure of the external shaft seal, lack of oil in the oil cup, or air leaks from plugged oil holes. Internal leakage may be caused by factors such as clearance gaps within the pump, the sealing surface of the exhaust valve seat, the sealing surface of the exhaust valve itself, the internal shaft seal, the pump cover surface, the intake pipe, and the seals on the gas ballast valve. Wear, corrosion, and seizing can all lead to increased operational clearances. If the oil hole becomes blocked, opening the oil-filling port will reveal that the pump’s noise level is reduced. Provided the oil tank is well-sealed, if you feel a suction effect when placing your hand near the exhaust port, it could indicate that the exhaust valve has failed.