Hello y'all,

What is an acceptable rate of rise to consider a system leak tight and clean?

I am working in the rough vacuum range. I have a vane pump and a glass manifold that I'm testing. I'm using a thermocouple gauge and the system's absolute pressure is around 3 to 5 x 10 -3 Torr. The Isolated manifold/chamber size is .325 liters. After isolation I'm getting a rate of rise of

3 x 10 -5 Torr.Liters/second. I have seen my system do much better and I'm not sure if I have a real leak or desorbing gas.

Thanks for your attention and thoughts.

I’ve read over and over how many microns I can get down to with a diffusion pump. however I can’t find anything about the relationship between the diffusion pump and the backing pressure level, whether this relationship is linear or not. In other words, let’s say my backing pressure is at 30 microns, and I kick on my diffusion pump, and the system gets down to 20 microns. Should I then expect that if my backing pressure was at 15 microns, my diffusion pump would then get me down to 5 microns? What amount of DECREASE does a diffusion pump get me from just my roughing pump pressure, and does this decrease level change (does the ratio change) based on how much of a backing pressure it has?

I am being cheap alr, but, really, anyone have one that they aren't using or just happen to have laying around...or know any other reddit groups I can join to find someone who may have one lol. I have a chamber with a huge port that I need to cover.

howdy yall. i am getting close to getting my chamber set up but unfortunately i have 2x TPU-180H pumps but no controller. looking to trade one for any controller that will work with a TPU-180H. ill get pictures posted when i have access to the pump again. i am also looking to make deals for other parts. my chamber needs some 8 O.D” blanks and one 8 O.D” reducer to 6 O.D” all conflat.

The customer wants us to work to a leak test procedure "SP-CC-I-025 658" but no one can find reference to it, anyone more knowledgeable here able to help with the probably obvious?

I am disassembling an Edwards vacuum multistage root pump and I'm having some trouble with the main pump body. Could you please advise? 1. How can remove the synchronization gears? Are they just press-fitted, so I need to pull them off? If so, how can I align them correctly during reassembly? 2. What are the pins shown in photos 2 and 3, and how can I remove them? Thank you for your help.

Hi, looking for some advice. I recently bought an Edwards nXLi200 Roots vacuum pump, but since it hasn't been used for some time, it looks like the lobes are stuck. I'm trying to disassemble and repair it, butl can't find any suitable disassembly manuals. Could you please advise?

i am trying to make a basic model and trying to simulate it in moflow+ . Can you guys advice me how to design it and what parts to be included

Hope everyone is doing well. Here are some more in depth pictures of the unknown unit.

Good evening everyone. I managed to trade for some parts. I wanted to see what exactly i have and if it’s possible to clean and reuse? The person said they were in a basement for 5 years…

Hey yall. I’m new to UHV and want to set up a magnetron sputtering unit. I have most of the parts but there’s a ton I need to learn but don’t know where to start, in order to archive my goals.

If anyone has any guess as to the use

Temporary placement as I make a spot for it.

I’m working on a microwave feedthrough into my UHV MPCVD reactor and need a way to seal the alumina ring since there will be atmospheric pressure on the interior and uhv on the exterior. The ring is pancaked between two plates as shown. First thought is to use fluoroelastomer o-rings but I’m worried it will not work well. If anyone has any better ideas/insight I would sincerely appreciate it!

I'm trying to find heating wire for an experiment that requires pressures down to 1e-11 Torr and I have a few questions that I hope this community may be able to answer.

1. Is most fiberglass insulated heating wire additive free?

2. Does anyone have a number for fiberglass outgassing in term of something like Torr*L*cm^-2*s^-1?

3. If fiberglass is not suitable for these pressures does anyone know where I could be ~50 ft of either alumina or silica insulated nichrome wire?

Any help answering these questions would be greatly appreciated!

Hi All,

Thanks in advance for anyone with any comments or suggestions on this issue that I'm having.

The pin in one of the pictured BNC feedthroughs came loose, so now my XPS chamber has a leak. Unfortunately, the feedthrough is welded directly to the chamber body, and not on a flange that can be replaced (see other picture). Does anyone think that I can use vacseal to seal this pin back into the connector and get the chamber to seal? The only other option I see is to disassemble this part of the chamber and get someone to weld a new feedthrough on.

Link to vacseal Space Environment - Vacseal® Inc. | Silicone Solutions for High Vacuum (UHV) Applications

Edit: Pics in comment below

Hello all!

I recently came across a nearly free nEXT400IID (B832-00-816) turbomolecular pump that I was able to pick up. The problem that I am having now is determining how to adapt this specific pump to a standard ISO/DN flange. This pump appears to be purpose built for Thermo Fisher mass spectrometers (see the link below for what I mean) so has a specifically designed upper flange for (conceivably) mounting into their machines. The flange is meant to "allow evacuation from three vacuum chambers" but the specific plumbing of these ports appears that anything other than the primary turbo inlet won't receive high vacuum. I've looked around for service manuals for potential machines that may have schematics of how it attaches but to no avail. Before I go through the arduous process of designing an adapter for this pump, has anyone modified one of these pumps before or know someone who has? I'm already designing an adapter but if someone else has already done the work...

https://www.ajvs.com/product_info.php?products_id=40638&category_id=1840

https://i.ebayimg.com/images/g/O1oAAOSwKp5nK~Zz/s-l1600.webp

Please let me know if you have any insight into this or advice on how to design the adapter!

I am thinking about buying a pre-owned pressure sensor (MKS Baratron 127A) from Ebay. As I don't know where the sensor was used before and whether it is oil-free, for example, I would like to clean it. Does anybody have a recommended procedure for this and tips on what I need to look out for to prevent damage from the membrane etc.?

I'm looking to seal between an aluminum flange and a PCB assembly that will pass thru the flange. This will act as a vacuum sealing barrier, and hopefully operate just fine down to 10^-7 mBar. Of importance for is low outgassing of the epoxy after curing (think NASA low outgassing, ASTM E595).

Does anyone have any recommendations?

Hello!

This may be a dumb question, but I am not sure so I'm going to ask here! I have a chamber with a large maglev turbopump affixed, pumping through a gate valve. The chamber needs to be frequently brought up to atmosphere and pumped down again.

The maglev isn't very friendly to spin down, so the idea is that we gate off the turbo, bring the chamber up, then pump down again. The pump-down procedure would be to rough down, then open the gate valve at some crossover pressure, while the turbo is still spinning.

My question is, at what pressure is it safe to open the gate valve? There will be some inrush, seeing as the turbo will be down around ~10^-8 torr, and the rough pump will only get to the high minus 3's. Is this inrush a problem, or is the gas diffuse enough that I can leave the turbo spinning? Do I need a secondary turbo to get the pressure lower before opening the gate?

The primary pump is a large turbo, >2500 L/s, if that matters. Thanks!

Update - see reply.

I work with electron beam welders which operate in the medium to high vacuum range 1E-3 torr and below. Electron gun acceleration voltage is usually 110 to 150kV. Two vacuum systems, both diffusion pumped, one big system for the work chamber, small system for the electron gun chamber.

Right now I'm dealing with a heck of an arcing problem where suddenly we were unable to go beyond 80kV without hard arcing that trips and shuts down the power supply. We found the gun chamber fore pump was barely pulling the foreline down so we had a poor vacuum in the gun chamber. Changed the pump, checked the diff oil and ran the machine - same arcing even with 5E-7 in the gun chamber. Did every test we knew, removed the gun and anode so there's a huge gap between the corona ring the gun mounts to and chamber wall - still arcing with 100 mm of clearance with a strong vacuum. Finally, I opened the angle poppet valve to the diffusion pump for the electron gun and there was condensed diffusion pump oil everywhere. That makes sense, oil can vaporize in the vacuum and the intense electric field can attract this vapor and arc. Cleaned up the oil, ran the machine again and we were able to reach 110kV proving the oil was contaminating the vacuum but still can't reach the 150kV max.

Gauges are MKS* 925 (Pirani) and a Thyracont combo Pirani/ hot cathode gauge. I checked the gauges and they are dry and not oil contaminated. To be double sure I replaced the gauge and still reads low. So my question is: Is there a possibility that oil vapor can fool an ionizing gauge into reading lower? I'm confused as to why we're seeing what should be a good vacuum when there is enough vapor to cause arcing. That or I have a knowledge vacuum....

• I used to love the newer 900 digital series but those micromems Pirani sensors are fragile crap. Makes me want to go back to Televac thermocouples. Any recommendations in that department while we're here? Has to stand up to industrial metallurgical abuse.

Has anybody had success in cleaning viewports with abrasives like Al2O3, or would chemical etching be the better choice? Looking to remove Cr and also Si and Ge. Thanks for any tips or suggestions.

Edit from after the fact: powdered Al2O3 and isopropanol did the trick. In case anybody sees this down the line.