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Subject: Re: Vacuum pumps
Date: Apr 22, 2:29 am
Poster: Dave Cooper

On Apr 22, 2:29 am, Dave Cooper wrote:

>Bidding on Varian SD-300 in VERY GOOD SHAPE, Alcatel 2033CP+ as roughing pumps - any comments? Very time sensitive... Not regarding the bid, any comments on the brands... Alcatel, Varian, Seargent Welch?....

I have used the SD-300 and Welch Pumps, no Alcatel experience. The SD's are direct drive which are running typically up to 5X the RPM of a belt drive pump. They are a bit smaller and lighter for the same capacity, usually reach a lower utlimate pressure, WHEN NEW. I have used an SD300 to reach about 8 x 10-6 Torr, way below the advertised 10-4 Torr. It was a new pump with a very clean Mass Spectrometer system, and I did give it lots of time.

To my ear at least), direct drives are less irritating to be around. The constant whirring sound is much less annoying than the ticka ticka ticka.. of the Welch, Belt drives.

But..... the Welch pumps run nearly forever... if you treat them to an annual oil change... and aren't put off by the shaft seal replacements, which are typically biennial and easy to do.

The innards are super hard steel and can really take serious abuse. The pyrolytic graphite seals are a bit delicate to install (just don't hammer on them) but the shafts seem to last and last. But... when the rotor gets worn... the ticking and clacking can be quite loud at low pressure.

In the direct drives, oil leaks typically come with wear on the shaft. Sometimes, new shaft seals will fix this. If not, it is NOT a simple low cost maintenance fix... since the pumps I have seen have the rotor and shaft as a one piece assembly. Worn shaft... replace the rotor too. $$$.

Hope this is helpful.

Dave Cooper