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A good deal.

Posted: Mon Sep 11, 2017 6:43 pm
by Finn Hammer
This pump, a VBC Microtorr became mine for around 100USD, some time ago, and with my newly gained ability to measure pressure, I thought it was time to start it up and check how it performs.
Of course, at that price, an Alcatel 3.4CFM pump is great in it's own right, when it comes with a small diffusion pump included, it gets much better.
I put the MKS 999 Quattro gauge on it and started the pump, and when it had become warm/hot after about a half hour, the pressure had setteled at 6.6Micron, which is not too shappy I should think. It is interesting how long time the pressure takes to drop, but it is good to get some hands on experience and get to understand how things work.
Opening the ballast does also open up to a heavy mist from the exhaust, so I will need to make an exhaust to the outside, but all in all this seems like a great deal.
IMG_20170911_185416.jpg
The new vacuum gauge readout in a second iteration, now fully battery powered. Disregard the "s"torr, being an artefact of experiments.
Turning the diff. pump on did make the preassure shoot up to over 100micron, but after 12 minutes, it setteled at 2.33 Micron, so there is some work to do with that pump.
IMG_20170911_192141.jpg
With the diff. pump, not a lot was gained. But of course, there has to be a reason for taking a pump out of service.
Anyway, good to know I did not throw money out the window this time.....

Cheers, Finn Hammer

Re: A good deal.

Posted: Mon Sep 11, 2017 7:41 pm
by Jerry Biehler
Work to do? It looks like it is working just fine.

Gas ballast opens the passage between the two stages to air to push out any condensable gases like water vapor and solvents. So if you were using it to desiccate something then you might use it but for general clean vacuum work stuff you dont need to use it.

Re: A good deal.

Posted: Mon Sep 11, 2017 9:03 pm
by Finn Hammer
Jerry Biehler wrote:Work to do? It looks like it is working just fine.

Gas ballast opens the passage between the two stages to air to push out any condensable gases like water vapor and solvents. So if you were using it to desiccate something then you might use it but for general clean vacuum work stuff you dont need to use it.
Jerry,

It is the diffusion pump, or perhaps the KF fitting between it and the Quattro that needs looking into.
The ultimate pressure of the diff. stage is 10E-6, and I am only getting 2.33E-3, so there is a long way to go.

Cheers, Finn Hammer

Re: A good deal.

Posted: Mon Sep 11, 2017 9:39 pm
by Andrew Seltzman
Be careful about connecting the quattro directly to the diffusion pump inlet without a trap, any back streaming oil vapor can damage the ion/pirani gauges.

Re: A good deal.

Posted: Mon Sep 11, 2017 9:47 pm
by Jerry Biehler
Ohh. Do you have enough oil in the diff? A little pump like that shouldn't take long to heat up and get going.

Re: A good deal.

Posted: Tue Sep 12, 2017 12:06 am
by Jerry Biehler
According to the manual you should have 55ml of DC704 in there. The instructions say how to empty it to clean so you might try emptying it into a beaker and measuring that.

Re: A good deal.

Posted: Tue Sep 12, 2017 1:50 pm
by Finn Hammer
Andrew,

I wonder what a proper trap would look like.

Jerry, I had already cleaned the pump as described in the manual, and also filled it with the 55ml of DC704.
Today I fitted a thermocouple thermometer to the heating element, and ran two separate pumpdowns, one with the thermocouple gauge, and one with a 901P

These are the data I get:
Udklip.JPG
The temperature is taken on the surface of the heating element, and there is _some_ temperature drop between element and diff pump vessel, however the tempereture is quite probably a lot higher than the recommended 220-230 degC.
https://diffusionpumpoil.com/diffusion- ... ure-guide/

The pump is an all sealed unit, so I guess there is litle that can be done with it.
I could cut it open and see the insides, perhaps attempt to weld it back together, but I am not sure it is worth the effort.
I have a brand new Varian HS-2 pump for the fusor, but this small pump would have been nice to use for smaller things, like glass work and calibrations.

Edit:

The pump had a lip weld at the bottom, which would lend itself well to a re-weld if should be, so I filed the seam off and took a peek inside the pump, this is what I saw:
IMG_20170912_171652 copy.jpg
A very small stack it has, and only 2 stages. To the left is the stack of my Varian HS-2 pump which, at 4 inches, is perhaps a bit too big but appeals to me a lot more.
The tiny ultratorr diff pump is going into storage for another time, when I have perhaps gained enough wisdom to appreciate it.



Cheers, Finn Hammer

Re: A good deal.

Posted: Tue Sep 12, 2017 5:11 pm
by Bruce Meagher
Have you checked transducer status @254T?;FF on you Quattro 999 to verify your hot cathode filament is ok (when the pressure is below 5mTorr)? As Andrew mentions make sure you have at least a 90 degree bend so the gauge doesn’t have line of sight to the pump. An instructive exercise would be to put your 901 gauge on the foreline with the Quattro 999 on the input of the DP, and then plot the two pressure curves together. From the picture you could have a leak in the DP housing (unlikely), the gauge, the kf fitting, or outgassing from contamination in the gauge or DP.

The boiler input power is directly related to the maximum pumping throughput of the DP. As long as you have enough cooling to support the input power, and the correct amount of DP fluid, I think the temp differential you are measuring from the bottom of the heater isn’t a sign of an issue.

Bruce

Re: A good deal.

Posted: Tue Sep 12, 2017 6:51 pm
by Nick Peskosky
Bruce nailed it before I had a chance to chime in as well. Check to ensure the Quattro is actually transitioning from the Pirani element to the hot-cathode sensing element in the gauge head. My Inficon BPG-400 will actually indicate a decrease in pressure and then between 15-30mTorr sensed pressure, increase in the reported pressure. This reported pressure increase also manifests itself again at <2.0E-5 Torr. [FWIW MKS should have a technical .pdf for this gauge head that displays the logarithmic Vout vs. Px graphs] I recommend checking the status of the cathode, degassing if able, and also pumping for a longer duration.

Re: A good deal.

Posted: Tue Sep 12, 2017 7:25 pm
by Finn Hammer
Bruce,
No I did not check transducer fault, and when I do over in the computer/electronics lab, I get @001ACKP;FF, meaning that pressure is too high to test.
I am starting to realize how ill equipped I am, having no powersupplies and PC's over in the mechanical workshop. I will look into that as a first thing.
Yes, I gues it is probably degassing that is the problem, a stern reminder to use more acetone...
I should also have pumped for a longer period, I see that now.
Thanks, all. I will regroup my gear and get back when I have something more usefull to say.

Cheers, Finn Hammer