Re: vacuum pump on da ebay

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Tim S <stm800@xxxxxxxxxxx>

becareful when reading the label printed on the pump as to the 
ultimate pressure it can obtain.ratings on pumps usually are taken 
with almost no volume on the inlet just the measuring device.and in 
the days of old the measuring device standard was the McLeod gauge.
<http://en.wikipedia.org/wiki/McLeod_gauge>http://en.wikipedia.org/wiki/McLeod_gauge

this type of measuring gauge only reads partial pressure not total 
pressure like a pirani type sensor does, so the readings of 
the  McLeod gauge look better than they actually are and are subject 
to calculation error of true compression ratio.
still today pump manufactures and slick marketing skills to sell 
their pumps state the lowest pressure on the datasheet.
this i have seen personally and is on one of the best days with 
everything connected to the system totally heated and outgassed from 
moisture to obtain this ultimate pressure.
you definately need a 2 stage pump and then a simple turbomolecular 
compression type to get below 1x10-3 ragge. thats 1 microm or 1 millitorr.

i could go on but that is enough for me.
email me off list if more info of the desired thought process if desired..

tim



Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: "Mike"

Also has a 2 stage that's rated .1 micron/millitorr. Always thought a
diffusion or turbomolecular was needed for that low (almost low
enough to make your own vacuum tubes/caps/etc).

Mike
----- Original Message ----- From: "Tesla list"
To:
Sent: Wednesday, August 09, 2006 10:31 PM
Subject: Re: vacuum pump on da ebay


>Original poster: Tim S
>
>i'd be really surprised if that old single stage would hit 15
>microns with a decent 2 liter of volume to be removed. new oil tko19
>will be needed aditional 20 dollars plus shipping a gallon container.
>
>i guess i'm just spoiled to have new 2 stage pumps that truly hit 4
>microns absolute pressure.
>
>all the best tim
>
>
>Tesla list wrote:
>Original poster: Ed Phillips
>
>Any of those three pumps would be useful. I'd be surprised if
>the last two go for under a couple of hundred bucks each and worth it
>if in decent shape.
>
>Ed
>
>
>
>
>