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Problem in getting high vacuum

Dear Sir,
I'm unable to get vacuum better than 2E-5 mbar in my E-beam evaporator after pouring LN2, though I had cleaned the DP and recharge with new DP oil. This problem I was facing since last 5 days, please suggest me what to do, I had checked all the joints , there is no leakage.
Thanks
Regards

Ramesh Sonkar
Student - IIT Kanpur, UP, India
October 14, 2009

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I would check the box for a foreign article such as a hammer which will outgas for days. Then I would check to see if you are getting the expected vacuum from the roughing pump. Do you have an intermediate turbo molecular pump?
When all else fails, call in tech services.

James Watts
- Navarre, Florida
October 14, 2009

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October 16, 2009

Dear Ramesh,
Your question reminded me of my days at IIT K about thirty years back! We had a DP where cooling had failed. The oil had decomposed and the whole pimp was dirty. These days better oil is available. I suppose you are using DC704 silicone oil. Of course, I am sure you wouldn't be using both DP & TMP together.
I suppose you were getting good vacuum before you had to clean the pump for some reason. I would look for the following.
1. Are you getting vac (0.001mb) only with RP. If not check all the 'o'ring joints and the quality of the oil in RP
2. Have you fixed the jet assembly properly i.e concentrically to the pump? Have you used required quantity of the new oil?Hope no part of the pump is left out!
3. Check the heater
4. What is the level of vacuum you are getting now? If it around ~10(-4) use the simple test of spraying petroleum ether near all suspected part and watch vacuum.
5. Of course look for hammers, screwdrivers etc inside the chamber. By the way what is size of your chamber and the capacities of the pumps?
6. Ensure all the needle valves, vent valves etc are closed and backing and roughing valves are working properly.

Good luck and happy Deepavali!

H.R. Prabhakara - Consultant
Bangalore Plasmatek - Bangalore Karnataka India

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We just had a similar problem. Turns out it was a bad vacuum controller.

Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover
San Diego, California
October 16, 2009