From: Slawomir Janicki <slawomir.janicki**At_Symbol_Here**COMCAST.NET>
Subject: Re: [DCHAS-L] water aspirator - vacuum question
Date: December 5, 2012 10:39:03 AM EST
Reply-To: DCHAS-L <DCHAS-L**At_Symbol_Here**MED.CORNELL.EDU>
Message-ID: <56FE609E-8FA5-448B-BBA4-EF98BCB90613**At_Symbol_Here**>

The KNF pumps and their OEM varieties (B=FCchi etc.) can last for a long time but are sensitive to the input stream. A disposable PP filter installed before the pump inlet extends the life of the pumps many times. There are two parts that can go bad:


-          valves (round rubber o-ring like flappers)

-          diaphragms (rubber Teflon coated circles)


Both are sensitive to even tiny amounts of solids in the input gas. When used for buffer filtration or in organic prep lab the filtrate can aerosolize and drying up droplets give solids. The solids stick to the valves and cause the pumps to lose vacuum. Replacing the flappers and cleaning the housing is time consuming.


Also, when the particles get past the valves they cause microscopic punctures in the Teflon lining of the diaphragms. Solvent vapors get to the rubber side of the diaphragms and delaminate the Teflon. Replacing the diaphragms is both time consuming and quite expensive.


With the filters I have used these pumps with good experience since the late 90’s. Here in MA we are not allowed to use water to run the aspirators, or even to cool reflux condensers.


Slawomir Janicki


From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**MED.CORNELL.EDU] On Behalf Of Ken Simolo
Sent: Wednesday, December 05, 2012 8:15 AM
Subject: Re: [DCHAS-L] water aspirator - vacuum question



On Dec 4, 2012, at 12:05 PM, Kristi Ohr wrote:

3.  House vac is fine for filtrations.  For rotovapping, you would likely need a pump for anything with a moderately high boiling point.  The diaphragm pumps are the norm these days for such things, but leave a lot to be desired in terms of performance and robustness.  They're also quite expensive to fix when they do (and they will) break.  For schlenk line work, belt driven pumps are dandy.



Not everyone's experience has been the same as this.  We have been extremely pleased in the use of diaphragm pumps for rotary evaporation.  We have been using KNF diaphragm pumps on rotovaps for over 8 years with only 1unit out of over 30 requiring a head rebuild (they abused the pump by literally pumping liquids and solids through it).  It was not that bad of a repair either.  I heavily researched which brand to get.  At the time when i called various pharmaceutical companies, I found out that some brands were requiring rebuilds every 1 -2 years but KNF was lasting 7 or more.  We have been extremely grateful that Steve Schifferle at Harvey Instruments had strongly recommended that we look into these pumps and to call the pharma companies to see what their real life experience was like.



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