Darryl Keil Last Activity 2026-04-22 11:25 AM
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dan

 
Subject : vacuum pump rebuild
Posted : 2003-04-06 1:16 PM
Post #28826
i have an old welch 1400 vaccum pump, oem spec .0001 mm hg vacuum,which is pulling very poor vacuum right now. I opened it up and inspected it, it is a two stage rotary vane pump, and saw that the rotors, end plates and cylinders are badly pitted and corroded. is it worth my while to take the parts in to a local machine shop to have the end plates milled flat and the cylinders bored, or would this be more expensive then the value of the pump?



 
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Darryl Keil

 
Subject : vacuum pump rebuild
Posted : 2003-04-06 2:46 PM
Post #28827 - In reply to #28826
Dan,When you say it pulling poor vacuum, what vacuum does it actually achieve?SincerelyDarryl Keil: i have an old welch 1400 vaccum pump, oem spec .0001 mm hg : vacuum,which is pulling very poor vacuum right now. I opened it up : and inspected it, it is a two stage rotary vane pump, and saw that : the rotors, end plates and cylinders are badly pitted and corroded. : is it worth my while to take the parts in to a local machine shop to : have the end plates milled flat and the cylinders bored, or would : this be more expensive then the value of the pump?




 
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dan

 
Subject : vacuum pump rebuild
Posted : 2003-04-06 7:32 PM
Post #28828 - In reply to #28827
It pulls around 20 mm hg: Dan,: When you say it pulling poor vacuum, what vacuum does it actually achieve?: Sincerely: Darryl Keil: : i have an old welch 1400 vaccum pump, oem spec .0001 mm hg : : vacuum,which is pulling very poor vacuum right now. I opened it up : : and inspected it, it is a two stage rotary vane pump, and saw that : : the rotors, end plates and cylinders are badly pitted and corroded. : : is it worth my while to take the parts in to a local machine shop to : : have the end plates milled flat and the cylinders bored, or would : : this be more expensive then the value of the pump?




 
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Peter W.

 
Subject : vacuum pump rebuild
Posted : 2003-05-10 1:45 AM
Post #28904 - In reply to #28828
: It pulls around 20 mm hgAs I understand the principle (I've never done veneering), the pressure is relative to atmospheric pressure (14.7 pounds per square inch). No matter how low the vacuum becomes, the pressure is limited to that of the atmosphere. At sea level, atmospheric pressure is about 760 mm Hg (29.9 in Hg). If you remove all of the air from a system, then the pressure will be 760 mm or 29.9 in. Hg. Therefore, if the pump pulls 20 mm Hg, then the pressure will be 97% of the atmospheric pressure. If you lived in Denver and your pump could pull 100% of the air out of your system, the pressure would only be 83% of that at sea level. If your pump can pull 25 in Hg or 685 mm Hg (110 mm vacuum) then you would be equivalent to doing your veneering in Denver. Can people in Denver do veneering or do they have to go to lower altitudes? I'm guessing that the lower atmospheric pressure, even at 12.2 psi, in Denver is sufficient.I'd keep the pump.




 
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Darryl Keil

 
Subject : vacuum pump rebuild
Posted : 2003-04-07 8:49 PM
Post #28832 - In reply to #28828
Dan,I would not have it machined. You will end up changing the tolerances which are key to achieving good vacuum. You may want to check with the manufacturer see if they have a rebuilding kit. Besides that I would ditch it. One other point. If your willing to let it run continously 20HG is usable.SincerelyDarryl Keil




 
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David B.

 
Subject : vacuum pump rebuild
Posted : 2003-04-09 8:22 PM
Post #28836 - In reply to #28832
: One other point. If your willing to let it run continously 20HG is usable.Darryl,That brings up a question that's been on my mind. Just how much vacuum do you really need? I made a homemade system, using a 3/4HP vacuum pump which we had on hand for another piece of equipment. The results were fine, but as part of an upgrade, I added a vacuum guage so I would be able to know what I had. It turns out I was only getting around 10"HG. I have since gotten it up to 20"HG (better gasketing), and of course the results are still fine, in fact, I can't tell any difference. So, how much is enough?Thanks for all your contributions to the world of veneering.David B.




 
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Darryl Keil

 
Subject : vacuum pump rebuild
Posted : 2003-04-09 8:58 PM
Post #28839 - In reply to #28836
David,In general I recommend 20HG or better with 15HG working a chunk of the time. 10HG is really quite low and personally I would not trust vacuum pressure at that level to give good result. Of course some veneers and some conditions will be acceptable at that level but many more, especially the ornery veneers will fail at 10HG. 20HG or better will give you good results in just about all situations.SincerelyDarryl Keil




 
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David B

 
Subject : vacuum pump rebuild
Posted : 2003-04-11 5:04 PM
Post #28843 - In reply to #28839
That makes perfect sense - I was using very flat (phenolic backed) veneer and flat substrates.Thanks again Darryl.
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