Welch 1376 questions

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Welch 1376 questions

Post by guest » Thu Aug 23, 2001 5:51 am

I found a Welch 1376 at the local general flea market for less than $100. Two questions nag me now.
1. The pump was virtually dry wen bought, I had to pour almost 3 litres of synthetic car-engine oil to get up to the marks on the glass. Now it pumps down my big dirty and leaky chamber to some 30..50 microns and will probably go lower when I find all the leaks and get the water out. This is good enough for me (as a starting point for diffs/turbos), but I worry if uising non-specified oil could shorten the life of the pump?
2. I read on the Welch web pages that this pump should not be run at atmospheric presuure for longer times. Now, when I fully open the ballast, the pump sounds (at least to my hairy ears:-) the same as when running at room pressure. Does this mean that one also must not run with ballast open for a longer time?
I can choke down the ballast intake so that the pump only says 'clunk' about once per second. Is this a better way to do it?

Thanks, Marko Cebokli

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Richard Hull
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Re: Welch 1376 questions

Post by Richard Hull » Thu Aug 23, 2001 6:38 pm

You can leave the ballast open for weeks on end while pumping with no problem. It will help elimenate water vapor from the oil. What they don't want you to do is run the pump with the actual hose intake sucking outside air into the running pump. ( a big No-No)

I would ditch that synthetic car oil real quick and get the proper high vacuum pump oil. It will not ruin your pump, but it might foul it with high vapor presure contaminants.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Welch 1376 questions

Post by DaveC » Sat Aug 25, 2001 1:16 am

I'd second Richard's advice there about the synthetic oil. Vac Pump oil here costs about 15-18$US/gal which is actually not far from the price of synthetic motor oil.
Also, having been drained when you purchased it, it might have had some rust on the pump chamber walls. If so, it is now dispersed in the oil, and could, in time, cause abnormal wear to shaft bearing surfaces and seals.

When you do drain and replace the oil, put in a small amount of the new oil and run the pump briefly, with the intake closed. Then drain that oil which will have the residue of the motor oil in it along with whatever dirt is left.
If it drains clean, just refill with pump oil and away you go. If the first flush is still dirty, flush again. Letting it drain a good while will reduce the numbre of flushes, too.

Dave Cooper

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Re: Welch 1376 questions

Post by AllenWallace » Thu Aug 01, 2002 4:08 am

I got the followng from a maintance manual for a Veeco leak detector with used Welch rotary vacuum pumps. This information should prove helpful to those of use who have Welch rotary pumps.

2. Mechanical Pumps, Cleaning

Mechanical pumps often become contaminated with large amounts of water and/or decomposition products from the oil diffusion pump.

a. To change oil, disconnect the pump from the system. Warm the oil by operating the pump with the intake closed, for approximately 15 minutes. Stop the pump and remove the oil drain cap. Most of the oil will drain out freely.

WARNING! Oil will be hot. The small residue remaining in the pump can be forced out by turning the pump pulley by hand, with the exhaust port closed and intake open. The oil will spurt out suddenly and should be deflected into the drain pan

CAUTION! Extensive operation with the exhaust port sealed should be avoided, as excessive internal pressure may loosen the shaft seal.

b. After removing all oil, close the drain and pour 3 or 4 ounces of clean Duo-Seal Oil into the intake port. Open exhaust port and run pump for a short period to completely circulate the new oil. Drain the flushing oil and force out residue, as above. Repeat flushing with new Duo-Seal Oil until flushing oil remains clean and free of color and foreign matter.

CAUTION! Do not use solvents or light flushing oils. Their complete removal is difficult and their higher vapor pressures will prevent the attainment of high vacuum.

c. After the pump is completely flushed, refill by pouring new Duo-Seal Oil into the exhaust port. Fill to proper level indicated on the sight glass. Replace dust cap. A gurgling noise is characteristic when high pressure air is drawn through the pump. It should disappear quickly as the intake pressure is reduced. If the pump continues to gurgle, the oil level may be too low. Insufficient oil does not give proper sealing or lubrication. Add oil through the exhaust port until it reaches the proper level. The oil level should be maintained between the marks on the sight glass, with the pump running. Level will drop when pump is stopped.

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Re: Welch 1376 questions

Post by Richard Hull » Thu Aug 01, 2002 5:23 pm

The key thing above is never drain or change the oil COLD.

I prefer not to disconnect the pump, but to operate it "in the system" until it is hot.......THEN disconnect and immediately drain, tipping the thing over to let the last bit of crud drain out.

I use a special flushing oil, as I have stated. Once the flushing oil is in, now I stop off the intake and run for just a very few minutes and dump the oil at the end of this time back into a container as it can be reused to flush another pump later. This assumes this is your nice pump which you have maintained well all along.

Note*** If the old original oil is really terribly filthy or if this is a first change for you on a new, used and unknown pump.........Do not save the flushing oil! You might have to give it a second flush with fresh oil.

Used pumps are often in an atrocious state as regards their oil. Their past owners treating them more like a service station air compressor than a scientific research tool.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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