1、 First of all, we need to know the type, characteristics and current situation of the two-stage rotary vane vacuum pump. Understand the use requirements and determine the repair objectives. Prepare the test method before maintenance.
2、 Judge the fault and confirm the fault. It’s easy to judge accurately. The diagnosis should be verified.
3、 To eliminate faults, first simplify, then complex, first easy, then difficult. Do not dismantle those that do not need to be disassembled. In order to reduce the new damage caused by the lack of special tools and improper operation, and reduce the position change and running in operation time. Generally speaking, the spliced rotor is not detachable, otherwise the form and position tolerance will not be guaranteed, and the rotor will be scrapped.
4、 For toxic, harmful and corrosive pumps, users shall be invited to clean them first and inform necessary protective measures to ensure the health of maintenance personnel.
5、 Fault classification
It is suggested to divide the faults into operation faults and performance faults.
Operation failure may include pump not running, performance failure may include limit pressure, limit full pressure, air extraction efficiency, noise, fuel injection, gas ballast performance, etc. which are not up to standard or fail to meet requirements.
6、 Examples of fault judgment and diagnosis
1) The vacuum pump does not run. If the condition is unknown, the pump cannot be started first to avoid aggravating the fault. Can and cannot be turned by hand.
The vacuum pump can be turned without turning. The causes can be coupling failure, belt slipping, wrong motor wiring, motor damage, power failure, etc.
The reason why it can’t be turned or heavy can be that the temperature of starting pump is too low and the viscosity of pump oil is too high; the reason of design and manufacturing is that there are too many oil returns from pump stop. Too much oil is returned due to too high oil level (too much oil is added, or water vapor condenses in the pump, or water flows back to the pump due to condensation in the exhaust pipe); there are foreign matters in the pump (welding slag and oxide in the intake pipe; debris of the pump parts such as the vane spring; the vane is deformed and stuck; there is occlusion (copper sleeve, rotor, middle wall, pump cover, stator, bearing).
2) The pump temperature is too high. It means that the maximum oil temperature measured near the low-level exhaust valve exceeds the value specified in the operation manual. Due to the increase of pump temperature, the viscosity of the pump oil will be greatly reduced, and the saturated vapor pressure of the pump oil will be increased, the ultimate pressure of the pump will be increased and the pumping efficiency will be reduced; the rubber parts will be easy to age; the operation clearance will be reduced due to the thermal expansion, especially the thickness direction of some non-metallic spinners and the clearance in the inner hole of the copper sleeve, which will affect the operation reliability of the pump. The reasons for the high temperature of the pump can be that the ambient temperature of the pump is too high, the air inlet temperature is too high, the air inlet cooling device fails, the inlet pressure of the pump’s long-term continuous operation is too high; the cooling water volume of the water-cooled pump is insufficient, the design effect of the circulating water is not good; the temperature control water volume regulating valve fails, etc.
3) Oil leakage. It can occur in the sealing surface of shaft seal, oil tank and pump parts, oil drain plug, oil mark, oil hole bulkhead, through-hole connection of stator part and support, air ballast valve (such as 2x-8), etc. 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 the pump is stopped, the oil will enter the gas valve, and oil may leak if the gas valve is not closed.
When making the self-made rubber pad, oil resistant rubber must be used. It should be in accordance with the original design shape. If the sealing surface is too large, it will leak oil if it is not pressed tightly.
4) Water leakage can occur at water pipe joint, water jacket cover plane, drain hole plug, drain valve, etc., water jacket drilling through, casting defects, frost crack, may also lead to water leakage.
5) High power exceeds the standard. It can be caused by too high inlet pressure, too high exhaust pressure for long-term continuous operation, occlusion of sundries entering, too high pump temperature, too small matching clearance of spinneret, too high voltage, too much pump fluid returning into the pump, etc., which will damage the motor. Long term continuous operation near the maximum power shall be avoided as far as possible. If there is sediment on the surface, it should be removed regularly.
6) The ultimate pressure is not up to standard.
It can be caused by external leakage, internal leakage, oil hole blockage, poor quality or pollution deterioration of pump oil, condensable substances such as water vapor, distortion of instruments and meters, abnormal operation of pump, etc.
When there is a lot of leakage, white steam can be seen at the exhaust port. There are many bubbles at the oil mark, and the hand can feel the exhaust pressure at the exhaust port. There are many bubbles on the oil surface at the low-level exhaust valve. Power will increase. At this time, first check whether the gas ballast valve has been closed. Since the limit pressure of each new pump is measured at the pump outlet, if there is any leakage, check the pump outlet, pipeline, valve and container one by one. The failure of the outer shaft seal, the lack of oil in the oil cup and the air leakage in the oil hole can also cause the outer leakage. The internal leakage can be caused by the movement clearance 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 air inlet pipe, the sealing parts of the air ballast valve, etc. Wear, corrosion and engagement will increase the running clearance. When the oil hole is blocked, open the oil filling hole to listen, the noise of the pump will be lighter. If the pump oil is clean in the oil tank and is not used for a long time, open the gas control valve to purify the water vapor in the pump. If not, check the meter. If the pump oil turns yellow and white and has been emulsified, fully open the gas ballast, adjust the air ballast for purification operation, and if necessary, put a proper amount of gas into the pump port for operation, so as to speed up the purification process. If other volatile gas or liquid is pumped in, the oil shall be changed in time, and the oil tank shall be washed if necessary. Some pumps will deposit pump fluid in interstage airway. In order to achieve good oil change effect, it is necessary to try to discharge the deposited pump fluid.
The ultimate pressure is measured by a compression type mercury vacuum gauge.
When using the calibrated thermocouple vacuum gauge and other full pressure gauges, the measured value will increase. Note that the gauge of thermocouple vacuum gauge should be calibrated in pairs. It is recommended to reserve a gauge calibrated at the same time for comparison in case of suspected contamination and distortion of the gauge.
The increase of the limit pressure will decrease the pumping efficiency in the period of high vacuum and increase the limit total pressure. Refer to the above description to judge, check and deal with the failure of air extraction efficiency reduction and ultimate total pressure rise.
7) Noise. The structure design of the pump, the noise of the motor and the pump bearing, whether the moving parts such as the rotating blade are smooth, whether the oil inlet quantity is too much, whether the noise and the air inlet quantity of the fan and the transmission parts are large, whether the parts in the pump such as the opening gas control operation and the oil baffle are loose, and whether the installation inequality causes the vibration, will affect the noise of the pump.
8) Fuel injection. To prevent the size, position and sealing condition of the oil return hole of the oil box for oil injection, the design and installation of the oil baffle, the demister, oil baffle cap and gas separator at the exhaust port, the height of the oil level and the size of the oil inlet will affect the oil injection of the pump. When the pump valve is open for air extraction, the air flow speed at the exhaust port of the direct coupled pump can be as high as 30m / s. when the oil level is opened, the circulating oil and air flow in the pump will be brought out The oil will test the measures to prevent oil injection.
7、 Other precautions
Some pumps have oil pumps, oil separators, one-way valves on the oil circuit, demisters, inlet filters (for preventing the return of oil and steam), inlet dust filters and other components or accessories, which should also be inspected. The failure of the oil pump will make the lubrication and sealing of the pump fail, the demister fail, which may increase the exhaust pressure, power and damage the motor. The failure of the inlet filter may increase the intake resistance, decrease the pumping speed and the pumping efficiency.
8、 Cleaning. It is not suitable for immersion, so as to avoid the detergent entering into the splicing and turning inside, which is not easy to discharge.
9、 Disassembly and assembly. It should be carried out in order according to the recommendations and regulations of the use instruction book, and the location should be recorded and placed reasonably to avoid wrong installation.