Vacuum Pump Oils-Inland 45 vs. Inland 45Z

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I went to order vacuum pump oil for work today, and was presented with an option I'd not previously seen.

My go-to product for a while now has been Inland 45. This is a full synthetic pump oil, and its primary advantage in my application is the lower vapor pressure vs. "standard" Inland 19. This is going in the roughing pump(backing a diffusion pump) in a mass spectrometer, so the lower vapor pressure means a lower hydrocarbon background in my vac manifold and better sensitivity. This has been documented well, enough that Hewlett Packard(now Agilent) started shipping and recommending the use of Inland 45 in pumps on their mass specs in the early to mid 90s.

In looking today, I saw Inland 45Z listed as an option. The only thing I can find is a vague "Higher Viscosity than Inland 45."

I'm using this in a tiny little Edwards E2M1 pump, which many of us consider massively underspecced for this application, but HP/Agilent still insists on pumps of this size for their benchtop GC-MSs primarily because they're quiet. They are run EXTREMELY hot. Even back in the early 90s, when HP still shipped the larger E2M2, people would replace them with larger pumps. In the past, I've run nearly all my instruments on either Edwards RV3 pumps or on my favored Varian DS102(each bests the other in certain specs, but they're both a nice, cooler running upgrade with more pumping capacity and with lower ultimate pressures vs. the spec pumps). For what I'm working with now, replacing the pump is not in the cards in the short term, so I'm making do with what I have.

In my mind, if Inland 45Z is truly higher viscosity, it would be beneficial especially given how hot these little pumps run. I'd expect less oil "fogging" on start up, lower backgrounds in the instrument, lower foreline pressures(I typically run ~20mTorr now capped, and about 50mTorr flowing 1ml/min helium into the chamber), and lower ultimate pressures in the instrument. I don't know if it's worth it though, and I'd be interested in hearing thoughts on this.
 
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"The only thing I can find is a vague "Higher Viscosity than Inland 45."

maybe the 45 oil is hard to get and they are changing over to the slightly thicker version bUT untill you get seecs on both all is a guess.

So stick with what you know works the 45
 

bunnspecial

Thread starter
Messages
1,337
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"The only thing I can find is a vague "Higher Viscosity than Inland 45."

maybe the 45 oil is hard to get and they are changing over to the slightly thicker version bUT untill you get seecs on both all is a guess.

So stick with what you know works the 45
As best as I can tell, the 45 is by far and away easier to get. I checked several suppliers and only a handful even list 45Z. One of my regulars, SIS, which is a big time aftermarket Mass Spec player(and one of the big advocates in the 90s of using 45+bigger pumps on HP benchtop mass specs) doesn't list it. I only ran across it at Capitol Vacuum, which I usually use for rebuild parts.

I suppose, though, that the fact that SIS doesn't carry it is good enough.
 
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