venting a UHV system


“Venting” a UHV system is the controlled way to bring the UHV recipient up to ambient pressure, typically in order to open it such that something can be fixed.

You can easily destroy something in the UHV system or vent parts which you did not intend to vent. So before venting make sure that

  1. everything in the system is turned off, especially ion gauges, ion pumps, turbo pumps and so on.

  2. you only vent the part of the system you want to vent, i.e. you have closed the valves to the 

other system parts. If you use electro-pneumatic gate valves, it is a good idea to take off the electrical connection of the valve, too, in order to prevent accidental opening.


For venting the system, one should use dry nitrogen rather than just air. A possibility for inserting the nitrogen into the system is a venting flange mid-way in the rotor set of a turbo pump. This is shown in on the image. A venting valve is attached to the flange and a transparent tube is used to get the nitrogen into that valve. In practice, this can be done by dipping the other end of the tube in liquid nitrogen. This will boil and fill the tube. You can take off the valve end of the tube, dip it in nitrogen and then put it on the valve again. In this way you are sure that the entire tube is filled with nitrogen. Venting should then proceed slowly, such that no liquid nitrogen makes it into the pump.


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