Maintenance mode of vacuum pump
The quality of vacuum pump depends on its mechanical structure and oil quality. It must be well protected when using vacuum pump. When distilling volatile organic solvents, the organic solvents will be absorbed by oil to increase vapor pressure, thus reducing the pumping efficiency. If it is acid gas, it will corrode the oil pump. If it is water vapor, it will make the oil into emulsion and destroy the vacuum pump.
Therefore, the following points should be paid attention to when using vacuum pumps:
Absorption devices must be installed between the distillation system and the vacuum pump.
Before distillation, the vapor of organic solvents in the system must be thoroughly pumped out by water pump.
If pumps can be used to pump air, then try to use water pumps, such as distilled substances containing volatile substances, you can first use water pumps to reduce pressure, and then use oil pumps.
The decompression system must be airtight, all rubber plugs should be of appropriate size and aperture, and rubber pipes should be vacuum rubber pipes. The ground glass is coated with vacuum grease.
Vacuum pumps can be classified into three categories according to their range of use and pumping efficiency.
(1) General pumps, the pressure can reach 1.333-100 kPa (10-760 mmHg) for "rough" vacuum.
(2) Oil pump, the pressure can reach 0.133-133.3Pa (0.001-1 mmHg) for the "sub-high" vacuum.
(3) Diffusion pump, the pressure can reach below 0.133 3a, (10-3 mmHg) is a "high" vacuum.
If you want lower pressure, you need to use oil pumps, good pumps can pump up to 133.3a (1mmHg).
There are two kinds of vacuum pumps commonly used in organic chemistry laboratories: water pump and vacuum pump. If the pressure is not very low, water pump can be used. If the pump is well constructed and the water pressure is high, the pumping efficiency can reach 106 7-3333 Pa (8-25 mmHg). The minimum pressure pumped by the pump is theoretically equivalent to the vapor pressure at the water temperature at that time. For example, when the water temperature is 25, 20 and 10, the pressure of water vapor is 3192, 2394 and 1197 Pa (8-25 mmHg), respectively. When pumping, safety bottles should be installed in front of the pump to reduce water pressure and reverse suction of water flow. Before stopping pumping, the pump should be deflated first and then shut down.
