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  • Maintenance of Vacuum Pump
    Jan 15, 2018

    The quality of the vacuum pump depends on its mechanical structure and the quality of the oil. It must be protected when using the vacuum pump. In the case of distillation of volatile organic solvents, the organic solvent is absorbed by the oil and increases the vapor pressure, which reduces the efficiency of evacuation. If it is an acid gas, it can corrode the pump and, if it is water vapor will make oil emulsion and the vacuum pump will be damaged.


    The following points must be noted when using a vacuum pump:


    ● Between the distillation system and the vacuum pump, an absorption device must be installed.

    ● The steam of organic solvents in the system must be completely removed by the water pump before distillation.

    ● Use the water pump as much as possible. If there is a volatile substance in the distilled substance, the pump can be reduce pressure by the water pump first, and then use the oil pump.

    ● Decompression system must be kept airtight, all the rubber plug size and hole to be appropriate, rubber hose to use vacuum hose. The ground glass is coated with vacuum oil.


    The vacuum pump can be divided into three types according to the range of use and the pumping efficiency:


    ● General pump, the pressure can reach 1.333 ~ 100kPa (10 ~ 760mmHg) for the "rough" vacuum.

    ● Oil pump, the pressure up to 0.133 ~ 133.3Pa (0.001 ~ 1mmHg) is a "second highest" vacuum.

    ● Diffusion pump, the pressure up to 0.133Pa, (10-3mmhg) is a "high" vacuum.


    The oil pump can pump lower pressure, and a good oil pump can pump out 133.3Pa (1mmHg) below.


    There are two kinds of decompression pumps commonly used in organic chemistry laboratory which are pumps and vacuum pumps. If there is no requirement for very low pressure, water pumps can be used. If the pump is well constructed and the water pressure is high, the Pumping efficiency can reach 1067~3333Pa (8~25mmHg). The minimum pressure that the pump can draw is theoretically equivalent to the water vapor pressure at the water temperature at that time.


    For example, the water vapor pressure is 3192, 2394, 1197 Pa(8-25 mmHg) when the water temperature is 25° C, 20 ° C and 10 ° C, respectively. Pumping with water pump, safety pump should be installed in front of the pump to prevent the pressure drop, the water flow suction; stop pumping before, you should deflate, and then turn off the pump.


    Lubricating Oil

    In the vacuum pump, vacuum pump oil not only as a vacuum medium, but also on the mechanical friction point lubrication, cooling and sealing effect. This is the most important performance of the vacuum pump oil, due to the vacuum pump requires a high degree of vacuum, the general use of paraffin-based narrow distillate lubricant. For diffusion vacuum pump, we can use silicone oil or other synthetic oil with low vapor pressure.


    Vacuum pump chamber volume changes continuously evolved to form the role of exhaust, and lubricating oil should have the appropriate viscosity and viscosity-temperature characteristics.


    Vacuum pumps continue to develop at a high speed. Due to the high friction between the vanes and the pump body, the oil temperature is increased, and the oil is easily oxidized and decomposed. In particular, the diffusion pump often operates under a very high temperature environment and increases the vapor pressure in the system. Decreased vacuum degree, vacuum pump oil is therefore required to have good thermal oxidation stability.


    If the vacuum pumps suck the corrosive gas, it will react with the oil and corrode the components in the pump. The inhaled air contains water vapor condensate, causing the vacuum pump oil to emulsify and corrode the metal, so it requires good corrosion resistance and anti emulsification.


    The main requirement is that the vacuum pump does not carry light components in order to avoid the saturated vapor pressure of the oil.


    The ultimate pressure is an important performance indicator of vacuum pump oil to understand the ultimate pressure of the vacuum pump at the lowest vacuum limit pressure.


    High Temperature of Motor

    The reasons for the high temperature of vacuum pump motor are analyzed as follows:


    (1) Large motor power, large working current and large calorific value.

    (2) The fan speed is low, the wind pressure is small, and the air volume is small.

    (3) The number of fan blades is less, and the amount of air produced is small.

    (4) The motor has dust and oil pollution, which reduces the heat dissipation capacity.

    (5) The bus voltage of the vacuum pump motor is 380V. Because the cable voltage drop and load distribution are uneven, the actual voltage added to the motor is only 365V, and the voltage is low, resulting in a large running current.


    Solutions

    The motor power and speed are matched with the vacuum pump, which cannot be changed. The fan is installed on the spindle of the motor. The speed of the motor is determined by the speed of the motor, and it cannot be replaced. Although increasing the number of fan blades can play a certain role, the dynamic balance is not easy to find after increasing the number of blades. If the right position is not right, it will cause the motor vibration to increase:


    (1) The original fan hood is lengthened 40cm, and an axial flow fan with the same diameter of the fan housing is added to it. The axial fan motor power is 850W, the speed is 1489r/min, and the voltage is 380V. The original fan continues to be retained. The axial fan has another power control, and the axial fan is not connected with the main motor. After the start of the vacuum pump to start the axial fan operation in time, the vacuum pump outage after 30min out of axial fan, so that the main motor is fully cooled;

    (2) Regularly remove the dust on the motor to keep the motor heat sink clean and increase its cooling capacity;

    (3) The voltage of the bus bar of the vacuum pump is adjusted to 400V.


    Result

    (1) As the axial fan speed is high, the wind pressure air volume is large, the cooling effect is greatly enhanced, the main motor temperature dropped 12℃ under the same ambient temperature and load current.

    (2) Axial fan can be artificially controlled, the main motor is out of service, the axial fan can still run, and the main motor can be fully cooled.

    (3) Try to balance the load distribution of the 2-phase busbar to prevent the voltage drop of some busbar due to overload.

    (4) After the voltage is adjusted, the operating current of the vacuum pump is reduced to 210A, and the calorific value is relatively reduced.

    (5) Slow down the insulation aging of the main motor, extending its service life.


    Smoking and Oil Injection

    (1) If the pump has just started to run and smoke, it is normal, if a long time in smoke is not normal

    Solution: the intake of the pump, including pipes, valves, and containers are repaired. After the leak detection, smoking will end.

    (2) Fuel injection shows that there are a lot of leaks outside the intake port, and even the air inlet exposes the atmosphere.

    Solution: seal the intake port of the pump and make the pump run. If there is no fuel injection, it is indicated that there are leak points, check the damage of the exhaust valve and replace the bad exhaust valve.


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