5973 vacuum system choice

[sllimbri]

If you were doing environmental work and were offered a 5973 ms, would you choose a turbo pump or a diffusion pump option and why?

[AICMM]

It would depend on if my environmental analysis were going to be the same for the next ten years. If all it had to do were VOA's I would chose the diff stack because it will not fly apart or seize any bearings. If I had to choose between semivoa and voa and swap columns to move back and forth I would be more tempted by the turbo with an eye to the potential future failure (expensive) of the the pump. This is because a turbo will pump down more quickly. The other thing I would think about is a no-vent option and staying with the diffusion pump option.

I have had very good luck with the diff. stack if you pay attention to a few key things like flow rates.

Best regards.

[Cmdr Keen]

If you're doing "normal" GCMS with standard applications I would always prefer the diff pump although everybody else will say the turbo pump is more up to date.
A diff pump is very very rough and doesn't need much service. Even the yearly recommended oil change can be skipped if you have your system under control and have a look at the oil when doing some service on the GCMS system.
If a turbo pump isn't neccesary because of pump down speed or special application issues (high flow rates e. g.) a diff pump is the cheapest and most confidental thing.
We operate a 5973N with a 6890 since 10 years and NEVER had ANY problem with the diff pump or the pre pump (Edvards). Two other devices with a Pfeiffer turbo pump get broken almost every two years (each time about 7000 Euro per pump) - just a short time after warranty period is over...!

[Bigbear]

My vote is a turbo. I have limited experience with diff pumps but that experience was not plesant. We had an early HP 5995 that backstreamed every time there was a power glitch. We also had a 5988 with two huge diff pumps.

We have 4 5973's the oldest dates from 1999, and have never lost a turbo. The only turbo lost was on a 5970 faairly early in it's life span. It was replaced with a Varian turbo with ceramic bearings and ran fine for years. When we retired it the pump was doing just fine.

just my $0.02.