Obtain Ultra-high vacuum method by oil diffusion pump

Oil diffusion pump is often used in high-vacuum pumping system by  taking some technical measures, you can get ultra-high vacuum and  the method is:

1. choose a good performance diffusion pump oil

Pump oil has a great influence on the ultimate pressure of the oil diffusion pump. Such as the use of 3 diffusion pump oil, the ultimate pressure can only reach 10 ^ -5Pa; instead of 275 silicone oil, the ultimate pressure can reach 10 ^ -7Pa, the ultimate pressure increased by 2 orders of magnitude. Second, the partial pressure of the evacuated gas also varies with the pump oil, which is the effect of the pump oil composition. To this end the oil diffusion pump to obtain ultra-high vacuum, you must choose a good performance diffusion pump oil. Diffusion pump oil requirements are: pump oil relative molecular weight to large, low vapor pressure at room temperature, thermal stability and oxidation resistance is better, the freezing point and low temperature viscosity is low, non-toxic, corrosion-resistant, low cost .

EVP diffusion pump oil as follows:

2. use a reasonable baking technology

Oil diffusion pump to obtain ultra-high vacuum system must be high-temperature baking, the purpose is to reduce the material out of gas rate. Materials in the atmosphere can absorb and absorb some of the gas, when in a vacuum, they produce desorption, the gas slowly released, in order to speed up the desorption, baking.

Different materials, the choice of baking temperature is also different. The principle is that the higher the temperature, can accelerate the gas, but also take into account whether the material can withstand high temperatures. Baking temperature to choose the right. Usually metal materials, such as stainless steel, baking temperature is 250 ℃ -450C; non-metallic materials baking temperature is 80 ℃ -100 ℃. Baking time 4h-8h above. Very high vacuum baking time in more than 24h. Typical metal oil diffusion pump system (after baking) performance and metal oil diffusion pump ultra-high vacuum system residual gas components.

3.increase the cold trap device to prevent pump oil reflux and migration

The phenomenon that the pump oil flows through the pump inlet to the drawn vessel is called back flow. The movement of oil molecules along the wall into the container is called reverse migration. Both the backflow and the anti-migration affect the vacuum system’s ultimate pressure. Cold trap is widely used in ultra-high vacuum system, which is installed between the pump inlet and the vacuum chamber, not only can effectively capture the diffusion pump reflux steam and partial split lysate, but also to extract the vapor from the vacuum chamber.

EVP cold trap using shutter type (A1, A2 type) and cone tower type (B1, B2) is shown as below:

4.reduce the anti-proliferation of gas pumping

Anti-diffusion of the evacuated gas is one of the factors that limit the diffusion pump to obtain ultra-high vacuum. Gas anti-proliferation and molecular quality, the smaller the quality, the more easily anti-proliferation. Diffusion pump hydrogen is easy to reverse diffusion to prevent hydrogen counter-diffusion There are two ways: First, reduce the diffusion pump outlet exhaust pressure, using two diffusion pumps in series to achieve; the second is the diffusion pump inlet pipe installation Liquid nitrogen-cooled titanium sublimes traps to trap counter-diffused hydrogen.

EVP offer a large number of diffusion pumps, pictures are as follows:

Tags:Oil diffusion pump,Oil diffusion pump oilCold trap

Edited by Nancy Zhang / EVP vacuum solution

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