Maintenance of two-stage rotary vane vacuum pump

Two-stage rotary vane vacuum pump maintenance

1. Current situation
First of all, we must understand the type, characteristics, and current status of the pump. Understand the use requirements and determine the repair goals. Before making repairs, prepare the detection means.

2. Failure judgment

Diagnose the fault and the diagnosis needs to be verified.

3. Troubleshooting

Simplify first and then complex. Do not disassemble what does not need to be disassembled. To reduce new injuries caused by lack of special tools and improper operation, reduce position changes and run-in time. Generally speaking, the spliced rotor cannot be disassembled, otherwise, the shape and position tolerance will not be guaranteed, and the rotor will be scrapped.

4. Harmful

For poisonous, harmful, and corrosive pumps, the user should be asked to clean them first, and inform the necessary protective measures to protect the health of maintenance personnel.

5. Fault classification

It is recommended to divide faults into operational faults and performance faults. Operational faults may include pump unrotating; performance faults may include ultimate pressure, ultimate full pressure, pumping efficiency, noise, fuel injection, gas ballast performance, etc. that are not up to standard or cannot meet requirements.

Two-stage rotary vane vacuum pump problem

1. Pump doesn't run

If the situation is unknown, the pump cannot be turned on first, so as not to aggravate the fault. 

If the pump can turn without rotating, the reasons can be coupling failure; belt slipping; motor wiring error; motor damage;

If it cannot be turned, the reason may be that the temperature of the starting pump is too low and the viscosity of the pump oil is too high; the reason for the design and manufacturing is that the pump stops and returns too much oil. If the oil level is too high, the pump stops and returns too much oil (too much refueling or water vapor condenses in the pump, or the condensed water in the exhaust pipe flows back into the pump); there are foreign objects in the pump (welding in the intake pipe) Slag, oxides; the debris of pump parts such as rotary vane springs; rotary vane deformation and jamming; occlusion occurred (copper sleeve, rotor, middle wall, pump cover, stator, bearing).

2. Pump temperature is too high

The highest oil temperature measured near the low-stage exhaust valve exceeds the value specified in the instruction manual. As the pump temperature rises, the viscosity of the pump oil will drop significantly, and the saturated vapor pressure of the pump oil will rise, which will increase the ultimate pressure of the pump and reduce the pumping efficiency; making the rubber parts easy to age; thermal expansion will reduce the running clearance, especially It is the thickness direction of some non-metallic rotary vanes and the inner hole clearance of the copper sleeve that affect the reliability of the pump operation. The reasons for the high pump temperature can be that the ambient temperature of the pump is too high, the intake air temperature is too high, the intake air cooling device fails, the inlet pressure of the pump is too high during long-term continuous operation; the cooling water volume of the water-cooled pump is insufficient, and the circulating water design effect is not good; Water regulating valve failure, etc.

3. Oil leakage

It can occur in the shaft seal, the sealing surface of the oil tank and pump parts, the oil drain plug, the oil mark, the oil hole block, the through-hole connection between the stator part and the support, and the gas ballast valve. It can be caused by aging of seals, improper installation, damage and failure, uneven surface, impurities, roughness, and loose castings. If the oil returns after stopping the pump, the oil will enter the gas ballast valve, and oil leakage may occur if the gas ballast valve is not closed.

When making a self-made rubber pad, be sure to use oil-resistant rubber, and follow the original design shape. If the sealing surface is too large, it will leak oil if it is not pressed tightly.

4. Water leakage

It can occur in water pipe joints, water hole screw plugs, water discharge valves, etc.

5. Power exceeding 

It can be caused by long-term continuous operation with too high inlet pressure, too high exhaust pressure, occlusion caused by debris entering, too high pump temperature, too small fitting clearance of rotary vanes, too high voltage, too much pump liquid returning into the pump, etc. will damage the motor. Try to avoid long-term continuous operation near the maximum power. If there are deposits on the surface, they should be disassembled and removed regularly.

6. The ultimate pressure is not good 

It can be caused by external leakage, internal leakage, blockage of oil holes, poor quality or pollution of pump oil, presence of condensable substances such as water vapor, distortion of instruments and meters, abnormal operation of pumps, etc.

  When there are a lot of external leakages, white steam can be seen at the exhaust port. There are more air bubbles at the oil mark, and the exhaust pressure can be felt by hand on the exhaust port. There are more air bubbles on the oil surface at the low-stage exhaust valve. Power will increase. At this time, check whether the gas ballast valve is closed. Since each new pump is shipped from the factory, the ultimate pressure is measured at the pump port, so if there is any leakage, the pump port, pipes, valves, and containers should be checked one by one. Failure of the outer shaft seal, no oil in the oil cup, and air leakage from the stuffy head of the oil hole can also cause external leakage. Internal leakage can be caused by the movement gap in the pump, the plane of the exhaust valve seat, the sealing surface of the exhaust valve, the inner shaft seal, the plane of the pump cover, the intake pipe, the seal of the gas ballast valve, etc. Wear, corrosion, and bite will increase the running clearance. When the oil hole is blocked, open the oil hole to listen, and the noise of the pump will be lighter. If the pump oil in the oil tank is clean and has not been used for a long time, open the gas ballast valve to purify the water vapor in the pump. If it is invalid, check the instrument. If the pump oil turns yellow and white and has been emulsified, the gas ballast can be fully opened, and the air ballast can be adjusted to purify the operation. If necessary, an appropriate amount of gas can be put into the pump port to run, which can speed up the purification process. If other volatile gases or liquids are pumped in, the oil should be changed in time, and the oil tank should be cleaned if necessary. In some pumps, the pumped liquid will deposit in the interstage air passage. In order to achieve a good oil change effect, try to discharge the deposited pump liquid.

The ultimate pressure is measured with a seated compression mercury vacuum gauge.

  When measured with a full pressure gauge such as a calibrated thermocouple vacuum gauge, the measured value will increase. Note that the gauges of thermocouple vacuum gauges should be calibrated in pairs. It is recommended to spare a gauge that was calibrated at the same time, in case of suspected gauge contamination distortion for comparison.

The increase in the ultimate pressure will reduce the pumping efficiency during the high vacuum period, and will also increase the ultimate total pressure. You can refer to the above introduction to judge, check and deal with the failures of the decrease of pumping efficiency and the increase of the limit full pressure.

7. Abnormal noise

The structural design of the pump, the noise of the motor and the pump bearing, whether the moving parts such as the rotary vane are smooth, too much oil intake, the noise generated by the fan and transmission parts, the intake air is large, the gas ballast is running, the pump internal parts are loose, vibration caused by the uneven installation will affect the noise of the pump.