What is the difference between small vacuum pump and large vacuum pump?

Large vacuum pump features: high power, high limit vacuum (absolute pressure minimum) (absolute pressure, the higher the representative of the vacuum degree is higher), and some can even do 10 negative Pa, very close to the theoretical vacuum. Pumping rate is large, usually " L/S (L / s) " as a unit. Industry has a very wide range of applications. Disadvantages: high price, large size, high weight, high noise, high energy consumption, the need for regular maintenance, not easy to move, etc.. Some large vacuum pump must use the vacuum pump oil or lubricating oil, the work will produce oil mist, the working medium has pollution. These shortcomings are particularly evident in some occasions, such as large vacuum pump, vacuum, but in low vacuum occasions but waste, like laboratory, just need to pump a small amount of gas gas sampling, gas analysis, gas circulation, vacuum adsorption, gas transfer, booster, indirect water absorption, drainage, etc., but exposed its many shortcomings. Therefore, this time with a small vacuum pump, vacuum (lower vacuum) can meet, and the volume is small, low noise, small power consumption, easy to operate, easy to carry, maintenance free, 24 hours continuous operation, but also allows the media rich in water. Most important, because it is dry, no oil, no need to pump oil or oil, so will not pollute the work medium, will not interfere with the analysis of the media, etc.. And the price is relatively cheap.