Vacuum

Joss Research: Vacuum: Diffusion Pumps

A Joss Research Institute
Informal Report:

Three Diffusion Pumps
and a Small Surprise


(13 September, 2008)

The Balzers Diff 650

This is the oldest of the three diffusion pumps that we seem to have here; it was recently given to us.

                       

As you can see, it is designed to pull 700 Watts at 110 V; I have no idea how much fluid it takes, or even what the proper fluid is.


The Big Varian in the Vacuum-UV Spectrometer

This pump actually seems to have a gatevalve on it, but I don’t think there’s a roughing pump in the box with it. It appears to have about a 6″ throat.

           


The Leak Detector

We seem to have a partly-disassembled leak detector. Here are some views of the guts:

           
           

The label is scratched up, and a bit difficult to read; the pump is a [rather old] Edwards SpeediVac 403A. It is water-cooled, has a 4″ throat, takes 100 cc of fluid, and pulls 500 W at 240 V. (I can make 240 V with a step-up transformer, and the heater shouldn’t care about the frequency.) I have checked the heater; it has reasonable resistance, and is not shorted to the case. So

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Joss Research: Vacuum: A New Manifold for the Roughing Pump

A Joss Research Institute Informal Report:

Construction of a New Roughing Manifold


(09 January, 2010, ff)

I am debugging a hollow-cathode laser head that I recently built, and having some trouble getting it to pump down to a suitable level. A good part of this appears to be an outgassing issue; silicone rubber caulk may not be particularly suitable for vacuum use, even at the minimal vacuum levels involved here. I have constructed a new active section for the laser, with epoxy joints; but in the meanwhile I also wanted to improve the performance of our little vacuum system in a general sense, and to change the manifold from a tangle of polyethylene tubes to something more recognizable. The poly tubing, on its own, pumped down to about 60 mTorr, which is not much of a vacuum even with just a forepump. (I have seen this pump reach 2 mTorr on the bench, running straight into a thermocouple gauge.)

Here are two photos, showing the initial version, before I added a connection to the laser:

           

(The Baratron tube [grayish blue cylinder with narrow red and silver band] is resting on a gray box that is not part of the » Read the rest

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Joss Research: Vacuum: Gross Leak Detection Techniques

A Joss Research Institute Informal Report:

Using an iPhone to Detect Gross Vacuum Leaks
and Making an Ultrasonic Sniffer for Smaller Leaks


(30 January, 2000)

I am debugging a largish nitrogen laser head that I have just built, and I wanted a good way to find the vacuum leaks that seem to be inevitable with any device of this sort. It is often possible to use a stethoscope with a small-diameter tube as its probe, but I have sometimes find it difficult to get good results that way, and last night it occurred to me that I should be able to use my iPhone with a hands-free device. (The opening for the microphone is no more than a millimeter across, and it is on a very small pod that sits on one of the earbud wires.) Rather than try to listen to the sound, however, I thought I would use an appropriate application to visualize the sound. (There are several of these; I chose one called Spectrogram.)

Sure enough, this technique is positionally sensitive, and at least for moderately large leaks it is quite good. As I continue working on this head I will have to deal with

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