[labnetwork] Backing Vacuum Pump - Dry pumps vs Oil Pumps

[Ian Harvey]

Dear Pradeep and all,

Here are some thoughts and experiences:

At Utah we made the conscious decision to move to dry pumps and not allow any wet pumps into the facility as we moved into our new nanofab.  We cleaned and PM'ed every tool that was previously on wet pumps, and used all new downstream hardware.

This decision was based on:

1) the observation of pump oil saturating the downstream exhaust system and mixing with hazardous reaction products to create dripping toxic cocktails. This greatly complicates any modifications to the exhaust line, places trade workers at risk during modification or demolition, and places the exhaust system itself under corrosive liquid attack.

2) Not concerned for back pressure events contaminating chambers but instead concerned for the steady state back diffusion of volatile oils into the deposition chamber.  This is something an anti-suckback valve will not help, nor will other schemes such as molecular sieves (after a short period).  I would be very interested in any data that peers have to validate empirical observation of delaminating or non-adhering thin films onto oil contaminated surfaces.

3) The contamination of the lab itself from the leaky pumps.  Each pump sits in a drip tray and the volatile oils soon coat every lab surface, creating slippery floors and loading the HEPA filters.  Some individuals are sensitive to the effects of prolonged breathing of these vapors in what is otherwise considered a clean-for-breathing airspace.

4) Once a lab is contaminated with pump oil it is very difficult and expensive to revert back.

I have also seen failed oil-sealed pumps backstreaming oil up into the nitrogen ballast line, so that the needle valve, bb-style N2 rotameter was bubbling in oil.  This resulted in back contamination of the "ultra-pure" nitrogen line.

I shudder to think of a decision to revert from dry back to wet pumps with all the ramifications such a decision entails.

—Ian Harvey


Ian R. Harvey
PRISM Cleanroom Director
Princeton University
70 Prospect Avenue, Princeton, NJ 08540

609-258-5922 (office)
609-285-9951 (cell)
iharvey at princeton.edu<mailto:iharvey at princeton.edu>
PRISM-Cleanroom.princeton.edu<http://PRISM-Cleanroom.princeton.edu>


Begin forwarded message:

From: Pradeep Nyaupane <nyaupanepradeep at gmail.com<mailto:nyaupanepradeep at gmail.com>>
Subject: [labnetwork] Backing Vacuum Pump - Dry pumps vs Oil Pumps
Date: November 3, 2019 8:21:06 AM EST
To: "labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>" <labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>>

Dear All,

 We have been using Dry pumps for turbo pump backing for Sputters, E-beam evaporators. And are planning to swap to oil pump with an anti-suck back valve, whenever required (in case dry pumps go bad).

We would like to know whether any of you are using oil pumps are being used as backing pump for Turbo / Cryo / DP.

Any advice / suggestions would be greatly appreciated.

Thank You in advance.

Thanks & Regards,
Pradeep Nyaupane

Technical Superintendent,
Equipment Maintenance Team In-charge,
IITBNF, Electrical Engg Dept
IIT Bombay, India
Tel No. 02225764471(O)
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