Chromatography Forum

Good to know, what vacuum units are you measuring; mTorr, Torr?

Sorry to jump around on units.

In HP/Agilent convention, I'm quoting foreline pressures in mTorr and hi-vac pressures in Torr.

The real fun ones are the Varian ion traps, where all the measurements are in millitorr. It can really leave you scratching your head when you see 10^-3 or so and wonder why on earth the pressure is so high. The Varian TQ is all over the place-the manifold is in torr, the collision cell in mTorr, and the source(which is somewhat separated from the rest of the manifold) jumps between Torr and mTorr depending on exactly what the pressure is/what mode you're using.

The concern over diffusion pumps was picked up by a coworker during an Agilent training session.

Here is a link to an older SIS article explaining why the small pumps get hot and fail:
https://www.sisweb.com/referenc/articles/sensit-1.htm

The concern over diffusion pumps was picked up by a coworker during an Agilent training session.

Here is a link to an older SIS article explaining why the small pumps get hot and fail:
https://www.sisweb.com/referenc/articles/sensit-1.htm

I'd be curious to know the full details on Agilent's reasoning. They DO say that their scroll pump can't be used with a diffusion pump, and I've been told tha thtis is because its pumping capacity isn't up to par.

The SIS article, which I've both read and referenced many times, makes the case for larger capacity pumps. SIS says they get better performance with a 100L/min pump located close to the 5971, and up it to 300L/min for remote mount pumps. It's worth noting that the RV3 is actually somewhat lower than this, at 2.3cfm(66L/min). My preferred Varian DS102 at 3.5L/min is right there.

All of these are still a lot higher than the E2M2 at 1.5cfm and E2M1.5 at 1.2cfm.

There again, referring to the SIS article, to my knowledge all 5971/5972s were fitted with diffusion pumps. The 5970 was always a turbo, and the 5973 and later offered both.

The concern over diffusion pumps was picked up by a coworker during an Agilent training session.

Here is a link to an older SIS article explaining why the small pumps get hot and fail:
https://www.sisweb.com/referenc/articles/sensit-1.htm

I'd be curious to know the full details on Agilent's reasoning. They DO say that their scroll pump can't be used with a diffusion pump, and I've been told tha thtis is because its pumping capacity isn't up to par.

The SIS article, which I've both read and referenced many times, makes the case for larger capacity pumps. SIS says they get better performance with a 100L/min pump located close to the 5971, and up it to 300L/min for remote mount pumps. It's worth noting that the RV3 is actually somewhat lower than this, at 2.3cfm(66L/min). My preferred Varian DS102 at 3.5L/min is right there.

All of these are still a lot higher than the E2M2 at 1.5cfm and E2M1.5 at 1.2cfm.

There again, referring to the SIS article, to my knowledge all 5971/5972s were fitted with diffusion pumps. The 5970 was always a turbo, and the 5973 and later offered both.

That is correct on the high vacuum pumps. I never understood why they didn't offer the turbo on the 5971/72, except there wasn't enough room in the form factor to fit the controller. I think there was a company that actually made a mod to put a turbo on them but that has been a long time ago.

We had two 5995s that had water cooled diffusion pumps on them that were as large as the whole 5971, that thing was terrible when a power outage occurred.

That is correct on the high vacuum pumps. I never understood why they didn't offer the turbo on the 5971/72, except there wasn't enough room in the form factor to fit the controller. I think there was a company that actually made a mod to put a turbo on them but that has been a long time ago.

We had two 5995s that had water cooled diffusion pumps on them that were as large as the whole 5971, that thing was terrible when a power outage occurred.

I've heard of a few folks fitting turbos to the 71/72, and it's something I'd be interested in doing if I had the spare time(and money). I imagine it wouldn't be a terribly "clean" install as you'd probably end up with an external/separate turbo controller.

On the 5995-is that the one you talked about a while back where the analyzer sits down inside the diffusion pump? I remember there being one that you said to ask Brenda if she would help me get it running and watch her throw something at me.

I'd be curious to know the full details on Agilent's reasoning. They DO say that their scroll pump can't be used with a diffusion pump, and I've been told tha thtis is because its pumping capacity isn't up to par.

My guess is that scroll compressors do not have stages that prevent backflow if power is interrupted. Also the precision fit of the contact area may not allow good ultimate vacuum; even though pumping volume can be high. Then there are the side vane seals as another leaking source.

I found an animation that may help....
https://www.youtube.com/watch?v=yNgqI4XPUZc

That is correct on the high vacuum pumps. I never understood why they didn't offer the turbo on the 5971/72, except there wasn't enough room in the form factor to fit the controller. I think there was a company that actually made a mod to put a turbo on them but that has been a long time ago.

We had two 5995s that had water cooled diffusion pumps on them that were as large as the whole 5971, that thing was terrible when a power outage occurred.

I've heard of a few folks fitting turbos to the 71/72, and it's something I'd be interested in doing if I had the spare time(and money). I imagine it wouldn't be a terribly "clean" install as you'd probably end up with an external/separate turbo controller.

On the 5995-is that the one you talked about a while back where the analyzer sits down inside the diffusion pump? I remember there being one that you said to ask Brenda if she would help me get it running and watch her throw something at me.

Yea that is the one, but the diffusion pump sits behind the analyzer. They look like you took a 5970 analyzer and mounted it with the interface going through the top of the GC and had clamshell doors enclosing the analyzer section.

I searched online and can't even find an image of one lol. Can find the MS Engine 5988/89 but not the 95s.