Common laboratory equipment and use of organic laboratory principle - vacuum pump

According to the scope of use and pumping efficiency can be divided into three types of vacuum pumps:

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

(2) oil pump, pressure up to 0.133 ~ 133.3 Pa (0.001 ~ 1mmHg) for the "second highest" vacuum.

(3) Diffusion pump with pressure up to 0.133 Pa and (10-3 mmHg) "high" vacuum.

Pumps and pumps are commonly used in organic chemistry laboratories for both pump and pump. Pumps can be used if low pressure is not required. If the pump is well constructed and pressurized, the pumping efficiency can reach 1067 ~ 3333 Pa ( 8 ~ 25mmHg). The lowest pressure the pump can draw is theoretically equivalent to the water vapor pressure at the time of the water temperature. 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.

To lower the pressure, it is necessary to use the pump, a good pump can be pumped 133.3Pa (1mmHg) below. The quality of the pump depends on its mechanical structure and the quality of the oil, which must be protected when using the pump. If the distillation of volatile organic solvents, the organic solvent will be the result of oil absorption increased vapor pressure, thereby reducing the pumping efficiency, if it is acid gas, it will corrode the pump, if it is steam will make the oil into milk Turbidity and vacuum pump. Therefore, when using the pump must pay attention to the following points:

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

Before distillation, the steam of the organic solvent in the system must be thoroughly drained by a water pump.

If you can pump the air, then try to use the pump, such as distillation of volatile substances can be reduced by pumping first pump, and then switch to the pump.

Decompression system must be kept airtight, all the rubber plug size and hole to be appropriate, rubber hose to use vacuum hose. Wear glass coated with vacuum grease.

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