Welch 1400 vacuum pump rebuild

[RLM56]

Hello Steve and everybody,

I'm finally getting around to posting a message and pics about the rebuild I did on a Welch 1400 pump.  It was an Ebay purchase and my first real vacuum pump.  It was cheap and so I decided to take a chance on it.  From what I could tell it's an old pump probably from the 50s and it was neglected for years on end.  The first time I plugged it in the stink from the oil exhaust was awful. I took a reading with an 801 gauge and 531 thermocouple tube donated by Steve Hansen and found it was pulling about 100 millitorr.  I flushed the oil several times with cheap vacuum oil and got it to 50 millitorr.  Still not great but improving.  Every time I flushed it I noticed dirt coming out with the oil so I decided to take it apart and clean it out.  I found about 1/2 inch of sludge in the botton of the oil case.  It was rusted inside the oil case and on the shaft inside the case.  There was some rust damage on the rotors and rings but nothing deep.  I removed the rust with Naval Jelly and wire brushing and fine sanding as needed.  I was careful with the shaft and rings/rotors.  The outer shaft seal was fused to the shaft and the exhaust reed valve was rusted off and no where to be found!  On starting the rebuild I looked up info from several sources and found a really good write-up on Sam's Laser FAQ site about vacuum pumps http://www.repairfaq.org/sam/lasercva.htm#cvadog  It's really extensive.  I was somewhat leery of buying one of the expensive rebuild kits and upon inspection of the inside of the pump I decided to make my own gaskets.  I used thin vegitable fiber gasket paper from McMaster Carr.  I used a good shaft seal from a Welch 1410 pump I had apart and got a replacement exhaust valve from the same pump.  That more than made up for the $10 I paid for the 1410.   There are no guide pins to help with alignment of the rotors and rings so without special tools the close spacing of the rotor to ring (the Duo-Seal) is accomplished by inserting a small slip of paper (onion skin paper or cigarette rolling paper works fine) between the ring and rotor at the seal area.  The paper maintains the spacing while you bolt the rings in place.  The paper later flushes out with the oil.  I don't remember where the paper trick came from but it works, might be in the stuff at Sam's.  The rest of reassembling the pump is straight forward and similar to reassembling a small gasoline motor.  I filled the pump with cheap Mobil Vacuum oil and ran it for a while to get the air out and warm things up.  I attached the 531 thermocouple and 801 gauge and started the pump again after several seconds the guage read 35 millitorr!  Over the next few days I kept running the pump to get water and air out of the oil and improved my mounting system for the 531 tube.  Slowly the needle on the gauge dropped to 30 then 25 then 20 millitorr.  Next I flushed the pump with real Welch Duo-Seal oil and that's when I got the best performance to date.....15 millitorr.

Thanks very much to Steve or I wouldn have a clue if I was doing anything right!!

Roy

See pics at    http://www.flickr.com/photos/32156795@N07/4327909205/

[jbin]

Could you explain a little more about your statement
 "There are no guide pins to help with alignment of the rotors and rings so without special tools the close spacing of the rotor to ring (the Duo-Seal) is accomplished by inserting a small slip of paper (onion skin paper or cigarette rolling paper works fine) between the ring and rotor at the seal area."

I have a 1402 I am cleaning up after an accident and I have a minor rebuild kit of gaskets, valves and springs, seals etc  but I have no info on the proper way to dissasemble/reassemble the rotors and rings.

Thanks

Jim

[RLM56]

Hi Jim,

First get a set of exploaded drawings from the Welch site.  http://www.welchvacuum.com/pdfs/manual/67-0777R2.9%20(DUOSEAL).pdf

You want to take pictures as you take it apart too, that never hurts and mark locations with a scribe or pencil lines.

The rotor is the thing with the slots for the vanes.  The rotor and vanes rotate in the ring.  There are two of each.  The rotor is offset in the ring so that it has one place where it comes close to the ring.  Notice on the inside surface of the ring in the area where the ring and rotor come the closest.  See that there?  There is a small scooped out area in the ring.  There is also a hole(s) machined through the ring that feeds to the exhaust valve(s).  At this scooped out section the rotor must be set very close to the ring, like .0001 inch or less so the oil can form a good seal.  That's what the rolling papers do.  You put two or more little slips of the paper that are about 1/4 inch wide and the height of the rotor on the rotor to maintain the small gap between ring and rotor during reassemply.  The rotor is keyed to the shaft so it's not going to move during reassembly.  The ring section mounts with several bolts.  The holes for the bolts are oversized to allow some play to adjust the clearence between the rotor and ring.  Stick the rolling paper slips to the rotor with a little oil.  Place the ring over the rotor and make sure the scooped out area and the rotor are in contact with the paper between.  Now hold the ring in place put the end plate and bolts on and tighten it up.  The paper will flush out the exhaust holes the first time you turn the shaft.  That worked fine for my 1400.  I'm looking at the 1402 drawings and it's larger and a little more complicated so you may have to adapt this method to fit the larger pump.

Good Luck,

Roy

[jbin]

Thanks for the description. I have successfully reassembled it now. 5 microns this morning :-)

[RLM56]

That's great!!  The one case when you want a project to totally suck!

Roy

[Probedude]

Notice on the inside surface of the ring in the area where the ring and rotor come the closest.  See that there?  There is a small scooped out area in the ring.  There is also a hole(s) machined through the ring that feeds to the exhaust valve(s).  At this scooped out section the rotor must be set very close to the ring, like .0001 inch or less so the oil can form a good seal.  That's what the rolling papers do.  You put two or more little slips of the paper that are about 1/4 inch wide and the height of the rotor on the rotor to maintain the small gap between ring and rotor during reassemply.  The rotor is keyed to the shaft so it's not going to move during reassembly.  The ring section mounts with several bolts.  The holes for the bolts are oversized to allow some play to adjust the clearence between the rotor and ring.  Stick the rolling paper slips to the rotor with a little oil.  Place the ring over the rotor and make sure the scooped out area and the rotor are in contact with the paper between.  Now hold the ring in place put the end plate and bolts on and tighten it up.  The paper will flush out the exhaust holes the first time you turn the shaft.  That worked fine for my 1400. 

Great description!  I've been looking for instructions on how to set the clearances on my Precision Scientific D25 and I think it's similar enough to the Welch 1400 that this will work for me too!  Regarding the scooped out area, if I remember correctly on my D25 I could move the outer ring so that the closest point I could move to be closer to the exhaust port.  That's how I assembled mine thinking that I should minimize the volume between the closest point of the rotor + ring and the exhaust port.  Then again I could align it so that the rotor and the ring would be nearly touching over a wider area - if that makes sense.  I wonder which it should be.

Do you remember if this too was something  you could do on your 1400? 

Thanks for any tips,
Dave

[RLM56]

Hi Dave,

Hmmm.. don't know anything about that pump.  But if it works in a similar way the most important thing is the distance between the rotor and ring.  It needs to be very close so the oil can form the seal.  So setting your pump up to make this clearance very tight would seem to be the best advice.  The 1400 has no provision for adjusting the point at which this seal occurs only the gap.

Roy