Type of vacuum pump

Vacuum pumps can be divided into three categories depending on the range of use and pumping efficiency:
(1) For general water pumps, the pressure can reach 1.333~100kPa (10~760mmHg) as "rough" vacuum.
(2) Oil pump, the pressure can reach 0.133~133.3Pa (0.001~1mmHg) as the "second highest" vacuum.
(3) Diffusion pump, the pressure can reach below 0.133Pa, and (10-3mmHg) is "high" vacuum.
The decompression pumps commonly used in organic chemistry laboratories are water pump and oil pump. If the pressure is not required, the pump 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 low pressure of the Zui pump can be theoretically equivalent to the water vapor pressure at the water temperature. For example, at a water temperature of 25 ° C, 20 ° C, and 10 ° C, the pressure of water vapor is 3192, 2394, and 1197 Pa (8-25 mmHg), respectively. When pumping with a water pump, install a safety bottle in front of the pump to reduce the water pressure and suck the water; before stopping pumping, first deflate and then turn off the pump.
For lower pressures, use an oil pump. A good oil pump can draw below 133.3Pa (1mmHg). The quality of the oil pump depends on its mechanical structure and the quality of the oil. It must be protected when using the oil pump. If the organic solvent with high volatility is distilled, the organic solvent will increase the vapor pressure by the oil absorption, thereby reducing the pumping efficiency. If it is an acid gas, it will corrode the oil pump. If it is water vapor, the oil will be milked. Drain the vacuum pump with the turbid liquid. Therefore, the following points must be observed when using the oil pump:
An absorption device must be installed between the distillation system and the oil pump.
The steam of the organic solvent in the system must be completely removed by a water pump before distillation.
If you can pump with a water pump, try to use a water pump. If the distilled material contains volatile substances, you can use a water pump to depressurize and then use the oil pump.
The pressure relief system must be kept tight and airtight. All rubber plugs should be of the appropriate size and size. The rubber hose should be vacuum hosed. The ground glass is coated with vacuum grease.

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