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Re: Vacuum Pump

Posted By: SVP Neon Equipment
Date: Saturday, 10 July 2010, at 2:12 p.m.

In Response To: Re: Vacuum Pump (Stephan Krasner)

> I'm using the pump for processing normal 10
> and 12mil tubing. Nothing elaborate like
> cold cathode or plasma work.

It doesn't have to be elaborate, but it does have to be "clean". For the sake of discussion, any size of neon tube from 5mm to 25mm is technically "cold cathode". The term refers to the type of electrode used, not the diameter of the tube. However, the operating current, in this context 30 mA to 250 mA+, determines the size of electrode used and also has an impact on how well the unit needs to be processed. As such, any luminous tube that operates like "neon" as we know it at 30-60 mA, and is internally bombarded (the common method in the U.S.), must be evacuated to less than 5 microns (millitorr - different name for the same measurement) before the glass temperature cools to below 175°C, with the final vacuum preferably less than that (think 1 or 2 microns).

> The guy I found is selling it for $150 and I
> got to see the demo in person. I'm not sure
> how good his gauge is, it's probably a cheap
> one, but it was meant for high vacuum. The
> range was -75 to +50 the needle went down to
> -71 cm hg when tested. I'm not sure what
> this would be in millitorr. Its not an old
> pump (MFD 2001) but he told me it got heavy
> use.

-75 to +50 what? Based on your next sentence, and assuming I am reading your numbers correctly and as intended, I will assume you mean -75 to +50 cm. This is not a high vacuum gauge at all - not even close. It is a *very* rough vacuum gauge. A high vacuum gauge never reads above ATM (usually no where close) unless it is a dual sensor, dual function gauge. In the high vacuum world these are not all that common and rather expensive for a "good one". However, in refrigeration service work (air conditioners, etc. where accuracy is not nearly as important) they are more common and, relatively speaking, cheap. And they are no where near as accurate - far from it.

Let's look at some numbers to see what kind of vacuum that pump is pulling. 1 cm = 10mm. So 75 cm = 750mm. (The accepted standard for atmospheric pressure at sea level is 760mm.) To go further, lets break the numbers down more. 1mm = 1,000 microns. So 750mm (75 cm) would be 750,000 microns (millitorr if you prefer).

You mentioned that you witnessed the pump pull down to -71 cm (-710mm, or 710,000 microns). To answer your question as to what that would be equivalent to in millitorr, it would be approximately 50,000 (FIFTY THOUSAND) millitorr! (76 cm - 71 cm = 5 cm, or 50mm = 50,000).

In a nut shell, the pump is junk. The MarVac you have works better if you are even able to light a tube with it to start processing.

There is some good info on my website if you care to take the time to read some of it. On the "Technical" page there are a number of articles including a vacuum levels chart. Here is a direct link to the vacuum levels chart:

http://www.svpneon.com/SVP_VacuumLevelsChart.html

Btw, ATM = 14.7 PSI = 760mm

Mark

SVP Neon Equipment

Messages In This Thread

• Vacuum Pump -- Stephan Krasner -- Friday, 9 July 2010, at 5:58 p.m.
  • Re: Vacuum Pump -- sean S -- Friday, 9 July 2010, at 7:23 p.m.
    • Re: Vacuum Pump -- SVP Neon Equipment -- Friday, 9 July 2010, at 8:24 p.m.
      • Re: Vacuum Pump -- Stephan Krasner -- Friday, 9 July 2010, at 9:59 p.m.
        • Re: Vacuum Pump -- SVP Neon Equipment -- Saturday, 10 July 2010, at 2:12 p.m.

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