{"id":1772,"date":"2016-05-24T15:47:02","date_gmt":"2016-05-24T22:47:02","guid":{"rendered":"http:\/\/www.rbdinstruments.com\/blog\/?p=1772"},"modified":"2021-05-24T04:36:55","modified_gmt":"2021-05-24T11:36:55","slug":"finding-vacuum-chamber-leaks","status":"publish","type":"post","link":"https:\/\/www.rbdinstruments.com\/blog\/finding-vacuum-chamber-leaks\/","title":{"rendered":"Finding Vacuum chamber leaks"},"content":{"rendered":"

When it comes to locating vacuum chamber leaks, there are a few different methods that can be used depending on the vacuum level of the leak.<\/p>\n

I like to categorize leaks into three types- Gross leaks, mid vacuum leaks and high vacuum leaks.<\/p>\n

Gross leaks are the type where the chamber will only pump down somewhere between atmosphere and the low 10-2 Torr range.\u00a0\u00a0 With this type of leak the vacuum is not good enough for an ion gauge to turn on.<\/p>\n

The first thing that you want to do with any leak is to make sure that all the flanges you worked on have been tightened correctly and appear uniform. If a flange has a wider gasket gap on one side than the other, then that flange may not be seated properly.<\/p>\n

Next you will want to make sure that your pump (usually a turbo pump) can reach vacuum when not pumping on the vacuum chamber. Then while monitoring the vacuum on your turbo pump or rough pump with a TC gauge, squirt some isopropanol or methanol on suspected flanges while watching the vacuum gauge.\u00a0\u00a0 Typically the vacuum will come down (pressure will go up) when the isopropanol or methanol finds its way into the leak. Then vent and replace the suspect gasket.<\/p>\n

The other technique useful for gross leaks is to slightly pressurize the system with nitrogen and then squirt the suspected flanges with Snoop<\/a> (or soapy water). For most vacuum chambers you do not want to pressurize them with more than 3 PSI. The reason that you do not over pressurize a vacuum chamber is because viewports are slightly concave and designed to hold vacuum, but not designed to hold pressure. Over pressurizing a vacuum chamber can cause the viewports to blow out \u2013 not good and also a safety hazard.\u00a0\u00a0 When you find the leak, you will see bubbles forming.<\/p>\n

For mid vacuum leaks, the ion gauge will function and the vacuum will be somewhere between the low 10-3 Torr and the high 10-8 Torr range.\u00a0\u00a0 For this type of vacuum leak, monitor the ion gauge while squirting some isopropanol or methanol onto the suspected flanges. In this vacuum range when the isopropanol or methanol makes its way into the leak, the vacuum may improve or degrade, but you will see a definite change in the vacuum. Sometimes the isopropanol or methanol will plug up the leak momentarily and the vacuum will improve noticeably. You can use a heat gun to evaporate the isopropanol or methanol on the flange where you noticed the vacuum change. Then after the flange cools down, repeat the procedure to confirm the location of the leak.<\/p>\n

For high vacuum leaks in the low 10-8 Torr to the low 10-9 Torr range, squirting the flange with isopropanol or methanol usually will not work. In those cases, you may need to use an RGA (residual gas analyzer) to find the leak. To use an RGA you would need to vent the chamber and install an RGA on one of the flanges, then pump back down and possibly even bake the chamber out depending on the level of the leak. For example, if the leak is in the low 10-9 Torr then you will probably need to bake out the chamber in order to get down that low.<\/p>\n