1) There is a "harmful space" in the structure of the pump, and the gas in the space can not be excluded. When the rotary vane turns the exhaust valve, this part of the gas is compressed and returns to the suction space through the gap between the rotor and the pump chamber, so there are always some gases exhausted each time. The smaller the "harmful space" is, the higher the limit vacuum that the pump can reach.
2) The pump chamber is divided into exhaust space and suction space by a rotary vane. Gas in exhaust space is compressed to more than O.1 MPa, while gas pressure in intake space is maintained at less than 1 Pa. There is a great pressure difference between the two. Therefore, the high pressure gas will break through to the suction space through various possible ways, so that the limit vacuum of the pump will be reduced.
3) Pump oil is composed of high molecular hydrocarbons. During the working process, because the high temperature of the friction surface in the pump is enough to split the oil molecules, a large number of light fractions (such as ethylene, acetylene and other hydrocarbons) with high vapor pressure are released, which reduces the limit vacuum of the pump.
4) The pump oil will dissolve a large amount of gas and vapor in the process of circulating flow in the pump body. At a certain temperature, the volume of gas in the oil varies with the gas pressure. When the pump oil enters the suction space, due to the reduction of the external gas pressure, the dissolved gas and vapor in the pump oil will be released again, filling the pump chamber, so that the pump will be under the limit vacuum.
In view of the above factors, in order to improve the ultimate vacuum of rotary vane pump, many measures have been taken, such as improving the processing accuracy of pump body, rotor and rotary vane, minimizing assembly clearance and harmful space, selecting metal with high strength, good corrosion resistance and compact as the material of pump body and rotor, and selecting soft metal as rotary vane. Material, so that the rotary vane and pump chamber surface can maintain good contact and so on.
没有评论:
发表评论