At present, oil diffusion pump is widely used in vacuum equipment, long platoon car and some production equipment in laboratory. Because the glass system is transparent, easy to observe the internal conditions, easy to detect and repair leakage, easy to make, cheap, and easy to remove gas, so although it is easy to break, the glass wall is easy to infiltrate helium, the volume can not be made very large, so the pumping speed can not be very large, but it is still widely used in the small and medium pumping speed range.
An improved diffusion booster pump of oil diffusion pump: Although the oil diffusion pump has been invented for many years, it still needs to be improved in order to expand its use. The direction of improvement is to increase the limit vacuum degree and the pumping range.
For example, the exhaust of vacuum smelting, semiconductor purification, special electric vacuum devices and electric light sources requires a large number of gases to be rapidly removed between 10-2 ~ 10-5 Torr. In order to create a noise-free and vibration free environment, the laboratory needs to stop the work of mechanical pumps for a long time. All of these put forward special requirements such as high limit vacuum, large exhaust volume and high front pressure resistant exhaust equipment. Any single oil booster pump or oil diffusion pump is difficult to meet the above requirements at the same time. Oil diffusion booster pump can undertake this task.
Because the partial pressure of the extracted gas above the steam flow is greater than the partial pressure of the gas in the steam flow, the gas molecules continuously diffuse from the higher pressure area to the steam flow in the lower pressure area, and are collided by the supersonic steam flow molecules, so the gas molecules get a velocity component that points to the front of the pump. From the macroscopic point of view, it seems that the gas molecules are gradually moved by the steam flow Push down. The original gas with large volume and low pressure, after several stages of steam flow compression, has become a gas break with small volume and high pressure (more than 10-3 Torr) when it reaches the front stage space, and then is pumped away by the front stage mechanical pump. The steam from the nozzle flows to the wall of the water-cooled pump, is condensed into liquid and flows back to the fractionator, and then heated to become steam. Such repeated circulation will gradually form a low pressure area at the upper end and near the nozzle, and the pressure in the pumped container will continue to decrease.
The high-speed steam flow acts as a barrier to the high-pressure gas in the front stage vacuum chamber, preventing it from returning to the high vacuum end. The high vacuum end pressure of this kind of pump can be as low as 10-8 Torr, while the front stage pressure can be as high as 10-1 Torr. Therefore, the gas compression ratio is as high as 100 million times, which is also an advantage that other pumps cannot compare. However, due to various reasons, the vapor molecules in the pump liquid will inevitably return to the high vacuum end and pollute the vacuum system and the pumped containers or devices, which must be eliminated. After many years of research on the pump structure and pumping mechanism of diffusion pump, the research on the oil retaining efficiency of various types of wells under different conditions, the research on the problems of diffusion pump fluid, oil return mechanism and oil retaining cap structure, the diffusion pump technology has made considerable progress: the pumping efficiency (he’s coefficient) can be greater than 50%, and the maximum working capacity per kilowatt is higher than 1 Torr · L / s, before The stage reverse pressure is better than 0.5 Torr, the limit pressure of direct pumping without cold well is up to 1×10-9 Torr, the pumping rate is twice higher than that of old pump, and the maximum allowable discharge pressure and durability are enhanced.
Generally speaking, the key problem is that the development of low vapor pressure pump fluid and backflow control makes it possible to use oil diffusion pump to obtain ultra-high or extremely high vacuum and “clean” vacuum. As long as it can completely prevent the influence of dissolved hydrogen in materials, thoroughly bake and degassing, and prevent infiltration, that is to say, minimize the pollution caused by the degassing of materials and pump walls, it seems possible to obtain the ultimate ultimate ultimate ultimate pressure strength of 10-16 Torr with diffusion pump at present.