How to inflate the turbomolecular pump? (1) Why inflation? When the turbo-molecular pump is shut down or running extremely slow, the pump will no longer have a compression ratio large enough (pressure gradient within the pump) to stop the hydrocarbons present on the upstream side from flowing back into the vacuum chamber through the turbine blades. This phenomenon is called anti-proliferation or molecular regurgitation. Under static conditions, when the pressure in the entire system is equalized, the partial pressure of the oil is usually 10-4 ~ 10-6 Torr (or 13.33mPa ~ 133.3μPa) on the foreline side and finally reaches the pump inlet. When the pump is turned off, properly aerating the pump is an effective measure to control the flow of oil molecules and to keep the vacuum chamber free of hydrocarbons. When the pump is stopped, hydrocarbon reflux quickly passes through the pump into the vacuum chamber. If the system remains under vacuum, the hydrocarbons will stick to the surface of the clean blades and vacuum chamber. When the system is subsequently operated, it will be extremely difficult to remove the adhering hydrocarbons. On the other hand, if the pump is filled with dry nitrogen or dry air while the turbomolecular pump is out of operation, the dry gas will provide a protective layer of gas to the exposed surface, and after the system is inflated, the refluxed hydrocarbon The compound, due to its ability to mix with the charged gas, has a very low adhesion capacity and has a very small percentage of hydrocarbons in the gas mixture and can be quickly evacuated on the next evacuation. (2) Delayed Inflation: Although it is generally accepted that the pump should be inflated after the pump is disconnected from the power supply, it is not uncommon for turbopumps to decelerate gradually after the power is turned off. If the delay is a few seconds or a few It will be better to re-inflate in minutes. During pump deceleration to 30% ~ 50% of its normal speed, the pump can still play the role of suction and compression. The vacuum chamber can effectively be placed in a vacuum state and hydrocarbon reflux can be prevented. Delayed inflation can also allow enough time to close the valve, in the case of frequent power outages, delayed inflation is useful. To delay inflation, the foreline vacuum must be maintained within the range of 1 to 1000 μmHg (1 × 10 -3 mmHg to 1 mmHg or 133.3 to 133.3 Pa) so there must be a vacuum valve between the turbo-molecular pump and foreline pump or Inside the foreline pump is a control valve that isolates the turbo molecular pump from the foreline pump when the power supply is interrupted. Otherwise, the foreline is inflated by the forepump and results in oil contamination. (3) where to inflate? Aeration of the turbo-molecular pump's anterior stage forces the hydrocarbon to flow immediately through the turbomolecular pump into the vacuum chamber. On the other hand, if the turbomolecular pump is inflated on the suction side, the purpose of covering the surface with the cleaning gas can be achieved. And the gas flow to the turbomolecular pump (from top to bottom), can temporarily stop and delay the hydrocarbon reflux, and some turbo-molecular pump in the middle of the compression stage between the inflatable, it and inflatable control of hydrocarbons in the suction side Backflow is almost equally effective. Inflatable at compression stage is especially superior in ultra-high vacuum systems. Because intermediate inflation does not require a costly metal-sealed, baked inflation valve. (4) How to inflate? If the turbopump is placed in a clean, dry environment, the air inside the chamber can be filled. However, the location of the inflatable entrance must be carefully chosen. If the inflation inlet is located close to the outlet of the oil-sealed rotary vane pump, the vapor contained in the gas will inevitably contaminate the vacuum system, and if the air is wet, Time, so to be filled with dry nitrogen or air filtered through the dryer. In addition, it is not always necessary to fill the gas under atmospheric pressure. If the pressure of the gas is several Torr (several hpa), the dry gas is enough to control the hydrocarbon reflux. More pump valve expertise, please see: Fluid Encyclopedia?