Hi Stewart and other Duo pump users,

Stewart, I am 99% sure you have a bad start capacitor.

The Duo 5 on our Delta Plus also failed to start after power outages.  We also spun it by hand to get it going.  We also would disconnect it from the mass spec to allow it to just pump room air to ease the starting.  Once it was warm it would run perfectly.

The solution is to replace the start capacitor.  (My assumption, based on the fact that it would run by manually spinning it, was that the capacitor was a start rather than a run capacitor).

Of course, Pfeiffer would not sell a capacitor nor had any info on the specs so we had to figure out the specs.  And, of course, Pfeiffer painted the capacitor and specs when they painted the pump.  By scraping the paint off the capacitor I was able to partly determine the specs.  

I purchased a replacement start capacitor at a local air conditioning supply shop for less than US$10.00.  The one that I purchased was a 15 microF, 370V.

Original had two black wires.  New had a blue and a black wire.  I was assured that the wire color was not important for this application.  One safety note - the new capacitor has exposed metal tabs to connect with spade connectors.  I installed the new capacitor in a small PVC tube to keep people from being able to touch the connectors.  Then I simply cable tied the PVC tube to the motor.

The pump now starts and runs perfectly.

Hope that this helps someone.


On Jan 9, 2013, at 8:50 AM, Bishop Stewart Eric wrote:

I experienced similar issues with the DUO 5 in our MAT 253 last year. Upon shut down or power failure( yes, it does occur in Switzerland) the motor energizes but the shaft jolts and holds and does not rotate. The solution was to remove the pump, plug it into an external power source, remove the motor fan cover, power on and manually turn the fan with a quick finger action. Run it warm and reinstall. It seems once it’s going it keeps going until it has no power again. This has worked successfully a few times now, we know the shaft or bearings are well on its way………but we managing to get full use of the pump.
Regards, Stewart
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Hill, John
Sent: 09 January 2013 11:04 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Duo 2.5 and DUO 5 Replacement
Hi David
We had this problem with the Duo 2.5 where the drive shaft fails. Pfeiffer wouldn’t repair it they just want you to buy another pump. The same with the DUO 5, they will not start so we disconnect the inlet and then run it for a minute or so then connect it back up. We are slowly switching over to using Edwards pumps although they are larger in size and put them outside the cabinet. We replaced the Pfeiffer DUO 5 on the MAT253 and the Edwards pump fits inside with one other inlet pump.
John Hill
Mass Spectrometry Facility
University College London
Chemistry Dept.
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Denhaan, David
Sent: 08 January 2013 17:50
To: [log in to unmask]
Subject: [ISOGEOCHEM] Duo 2.5 replacement on the Delta V
Dear List,
The Duo 2.5 roughing pump on my Delta V failed and I need a replacement.  Pfeiffer no longer sells that model.  Can I use their Duo 3?  Peiffer wasn’t sure if there were any modifications needed for use on the Delta V.
David Denhaan
Ames, IA

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