GNB Baffles Dramatically Reduce Backstreaming

While commissioning a large vacuum coater we encountered a serious problem with oil backstreaming from the halo-baffle-equipped 32 inch diffusion pumps. After only a few days we would see DC-704 silicone oil dripping from components situated above the throat of the diffusion pumps. This level of contamination was unacceptable for our process.

We surveyed the manufacturers of chevron baffles and selected GNB because of their low price and low-profile design. Their design made it easy for us to fit the chevron baffles between the pump inlet flange and the valve above. GNB quickly fabricated two of their 32” multi-coolant chevron baffles and shipped them to us. We removed the halo baffles from two of the diffusion pumps and replaced them with standard cold-caps. Then we installed the chevron baffles above the diffusion pumps and cooled the baffles with 15C water. The only additional components required were some longer threaded rods for the pump’s inlet flange and a short extension for the pump’s foreline.

The results were dramatic. The backstreaming rate dropped to about 6% of the rate generated by the halo-baffle equipped pumps. Lower backstreaming rates could be achieved by cooling the chevron baffles to a lower temperature. However, this rate was small enough to be acceptable for our purposes. The surfaces above the pump went from dripping wet to faint oil deposits that were only detectable by weighing witness samples on sensitive balances.

The overall pump speed of the pumping system dropped to only 87% of the speed achieved with the halo-baffle equipped pumps. If we assume that the pumps were pumping at their rated speed of 25600 liter/sec, we calculate that the conductance of each chevron baffle is about 6500 liter/sec.

In conclusion, we found that for our system, we eliminated a contamination problem at a minimal penalty in the overall pump speed of our system by using GNB’s chevron baffles.

Baffle Backstreaming (xls)
Baffle Pump Speed Test (xls)

Paul Diffendaffer
CEO, Venture Technology, Inc.

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July 31, 2009

View Original Letter (pdf)

Dear Ken:

I thought it might be appropriate to share with you my observations on “what it is like” to be a GNB customer.

As you know, in my past life as President-CEO of Denton, we had the occasion to use GNB on several occasions.  Build quality was excellent but there was always “something lacking” during the process.  Sometimes it was a failure of the GNB engineering team to be proactive.  On some occasions communication was poor.  In other cases mysterious schedule slippages occurred.  None of these were deal killers (as the final build quality was ALWAYS there) but the overall end feeling was akin to eating “lite” ice-cream.  Nice, but not completely satisfying.

Under your tenure and the changes that you and your team have instituted, a literal transformation has occurred.  The bar on build quality has been raised; the new chamber I commissioned from you at RNT exceeds (I didn’t think it could be done!) the performance of the “mother” chamber GNB  built for me 4 years ago at Denton.  GNB’s sales team was proactive, tenacious, and persistent; working with me to drive a design that met my budget and performance requirements.  Your engineering team is crackerjack; they took ownership of the project and drove me to make the decisions necessary to keep the project on schedule and on budget.  I particularly enjoyed the collaboration between your sales and engineering team and how if I missed a deadline on responding, a polite reminder came back to me from two directions.  I was kept abreast of the project on a regular basis and in the end, you hit the schedule exactly.

With performance like this there is no reason anyone should consider going anywhere else!

I now consider you folks “Hagen Daz” !

Best regards,
Frank T. Zimone
Vice President - Operations