How is it the Vacuum Pump Becomes Sluggish in Use?
If the vacuum pump becomes sluggish, check the following three problems:
If there is no problem with the pipeline, it is generally caused by excessive wear of the blade in the pump body
If it is a vane vacuum pump, check whether there is oil.
If it is a water circulation vacuum pump, it is necessary to check whether the vacuum pump has been dehydrated.
Here are some common sense of vacuum pump maintenance:
The quality of vacuum pump depends on its mechanical structure and oil quality. When using vacuum pump, it must be well protected. If the volatile organic solvent is distilled, the organic solvent will be absorbed by the oil. As a result, the vapor pressure will be increased, thus reducing the evacuation efficiency. If it is an acid gas, it will corrode the oil pump. If it is water vapor, it will make the oil into emulsion and pump out the vacuum pump.
Therefore, the following points must be paid attention to when using the vacuum pump:
Between distillation system and vacuum pump, absorption device must be installed.
Before distillation, the steam of organic solvent in the system must be completely pumped out by water pump.
If the pump can be used for air extraction, the water pump shall be used as far as possible. If the distilled substances contain volatile substances, the pump can be used for pressure reduction first, and then the oil pump shall be used.
The decompression system must be kept airtight, all rubber stoppers should be of proper size and holes, and rubber tubes should be vacuum rubber tubes. Apply vacuum grease to the ground glass.
According to the scope of use and pumping efficiency, vacuum pumps can be divided into three categories:
(1) In general, the pressure of water pump can reach 1.333-100kpa (10-760mmhg), which is “coarse” vacuum.
(2) The pressure of oil pump can reach 0.133-133.3pa (0.001-1mmhg), which is a “sub high” vacuum.
(3) Diffusion pump, the pressure can be up to 0.133Pa or below, (10-3mmhg) is “high” vacuum.
If the pressure is low, the oil pump must be used. A good oil pump can pump up to 133.3pa (1mmhg).
There are two kinds of pressure reducing pumps commonly used in the organic chemistry laboratory: pump and vacuum pump. If the low pressure is not required, the pump can be used. If the pump is well constructed and the water pressure is high, the evacuation efficiency can reach 1067 ~ 3333pa (8 ~ 25mmhg). The lowest pressure the pump can pump is theoretically equivalent to the water vapor pressure at that time. For example, when the water temperature is 25 ℃, 20 ℃ and 10 ℃, the pressure of water vapor is 3192, 2394 and 1197pa (8-25mmhg), respectively. When pumping with water pump, safety bottle shall be installed in front of the water pump to prevent water pressure from dropping and water flow back to suction; before stopping pumping, air shall be discharged first and then the water pump shall be shut down.