Vacuum pump rebuild

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Bruce Meagher
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Re: Vacuum pump rebuild

Post by Bruce Meagher »

Thanks for the pictures Rex, and the data point with the small pit on your first motor.

I don't know what I was thinking last night. Clearly you can only remove a very small amount of material from the cylinder or rotor while still maintaining the oil seal at the top between the rotor and stator. We'll know more about the condition of the pump internals this weekend.

Bruce
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

Rex did a good job on the 1402 oil reservoir. I love that he noted the vacuum didn't improve all that much, if at all.

I have always said let the sleeping dog lie. I have two 1402's here. I rate them as one of the finest pumps ever made by anyone.

I bought my first one over 18 years ago. It pumped down with dirty oil to 15 microns. I drained the oil after a 1 hour run. It was a bit rusty and filthy as well. I reloaded TKO pure oil and ran for 3 hours. Drained and the oil was murky but cleanish. I finally reload with good belt drive oil and it pulled down to 5 microns. I never looked inside. At 5 microns it is a good pump.

TKO oil is flushing oil made specifically as a thin pump cleaning oil.

The second pump I picked up at a hamfest. I could see no oil in the pump at all. The drain plug yielded about a cup of grime and sludge that oozed out. I dare not try to hand rotate the pump pulley.

I mixed TKO 50:50 with Marvels Mystery oil and filled the pump. I let it set for 1 week, after which time I tried to turn the pump wheel and it broke loose from a locked condition fairly easily. I turned it by hand for several turns and was smooth. I ran the pump for only 5 minutes and then drained a pure rust colored ruby red oil. I reloaded this time with TKO and let the pump run for a full hour and the pressure was down to 20 microns. (Marvels Mystery oil has fractions that create vapor from that first fill.) I drained again and the oil came out only slighly rusty but without sludge. A final filling with real pump oil and the pump went to 10 microns. I ran it with this oil fill on and off for a week and on the final day it pulled to 12 microns.

One final drain had the oil fairly clear of rust and just a little light gray near the end of the draining, (sludge). A final last fill with oil and the pump pulled to between 5 and 8 microns. I have left this pump sitting for 8 years. About 6 weeks ago I used it to evacuate a discharge tube that I was testing and it pulled to 10 microns after 10 minutes of gas ballasting.

Two sleeping dogs restored with no peeky up their skirts to see what was really there. For my money if your old used pump gets down under 15 microns, your pump is good enough. A nice sludge lining that allows the system to pump to that level can be left in the oil reservoir. If you change your oil in heavy use as required, it will ultimately work its way out in the draining.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I took apart the pump this morning. The first picture is the pump. It is only three inches long but it does all the work. You can see the little coupler that attaches the motor to make the pump turn. The second picture is looking down at the pump. The third picture is the first stage and second stage split apart. The U shaped cutout is what connects the two stages together. The fourth picture is everything inside disassembled. I didn’t take the vanes out of the rotor yet. The last two pictures are the first and second stage chambers. They have some rust so the pump might not work well when I put it back together. I’m going to clean everything, and then put it all back together.

My dad is also going to help me learn how the pump works in more detail.

Tyler
Attachments
The pump and coupler
The pump and coupler
Top view of pump
Top view of pump
First and second stages split
First and second stages split
Pump disassembled
Pump disassembled
Second stage chamber
Second stage chamber
First stage chamber
First stage chamber
Rex Allers
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Re: Vacuum pump rebuild

Post by Rex Allers »

It looks better than one might have expected from the rust caked picture a few days back.

You might want to try electrolytic rust cleaning on the pump parts.

Hope there's still some life in it that you can save.
Rex Allers
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I used simple green to get the oil off the pump parts, and now they are in the electrolysis bucket. It’s a 5 gallon bucket with 1/3 cup of washing soda and 4 gallons of water. A 12V DC power supply is connected to 4 pieces or rebar. I hung the parts in the water from a metal bar. The bar is connected to the negative side of the power supply. I don’t really understand how it works, but it sure does remove the rust.
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IMG_0657.JPG
John Futter
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Re: Vacuum pump rebuild

Post by John Futter »

Tyler
your father has introduced you to the magic of reduction
in this case iron oxide is being reduced back to iron.
this process is used by vintage experts to reclaim old engine parts left out in the weather for 50 years or more.

Note to others if it is a saltwater corrosion you have to use a different electrolyte -- google it!!
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I finished cleaning all the pump parts. I have also been studying how the different parts fit together and make the pump work. I will post more about that after I have the pump running. Below are pictures of my progress. The first one is of the whole pump cleaned and ready to be assembled. The next four pictures show the pitting on the rotor and stator. The wire in the picture is 0.004” in diameter to help understand how big the damage is. The next three pictures are the pump being assembled. Next week I’m going to attach the motor and see how well it works.

Tyler
Attachments
Pump parts cleaned
Pump parts cleaned
Rotor pitting
Rotor pitting
Rotor pitting zoomed
Rotor pitting zoomed
Stator pitting
Stator pitting
Stator pitting zoomed
Stator pitting zoomed
Second stage assembled
Second stage assembled
First and second stages
First and second stages
Assembled pump ready to be attached
Assembled pump ready to be attached
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

In my previous posting in this thread about rebuilding my Trivac D16 I mentioned the damage caused by a split-pin holding the rotor to the main shaft that disintegrated in the pump. It was mostly to the stator walls, rotor sides, vanes and they were pretty deep since the pin was made of hardened steel(similar to your photo but not as distributed) .

Two things to note here however. My pump uses vanes on the rotor. This allowed me not to worry too much about how much metal I removed from the stator (photo in previous post) and second, as stated by the rebuild manual, scratches at the ends of the rotor or the center rear bearing will cause poor pump performance. To repair these areas I used Permatex cold weld or some metal epoxy with similar expansion coefficient and adherence. It is an epoxy with metallic filling. Cleaned with methanol (hot) and acetone. Waited two days after the epoxy and machined and sanded the ends smooth while keeping the original rotor thickness identical so the epoxy only filled the damaged area. As I mentioned it has been running perfectly for 10 years now since there are little contact there apart from the pump oil.

Same process with your pump might work for you, as long as there is no metal to metal contact with the rotor in those areas. Another option is plasma torch buildup as used in repairing car crankshafts and valve lobes. Your local machinist might be of help here and hone the stator cylinder for you. Same for the rotor.

Looking forward to seeing your progress.
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

I follow with great interest this adventure and love's labor into the attempt to restore a pump that under any reasonable and cogent examination would be instantly and unquestioningly consigned to the scrap metal pile.

If billed for labor at a mid-range figure for metal cleaning, electro-chemical activities and machining of $40.00 per hour, coupled with the supplies consumed would make the effort of saving this pump exceed the price for a brand new pump by two or three times!

It is also noted that if even only moderately successful, the "hands-on" knowledge gained and the extent of the effort involved in this attempt might well be priceless in that it will lead to successful future efforts when one is "up against the wall". The "hands-on imperative" drags one not only to greater mechanical prowess, but also to gained knowledge and advanced creativity and inventiveness as all of these skill sets are often pressed into service and even tested to their limit.

Again, this is a fascinating and heroic thread about the "doing".

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

Quote Richard:
""It is also noted that if even only moderately successful, the "hands-on" knowledge gained and the extent of the effort involved in this attempt might well be priceless in that it will lead to successful future efforts""

Have to agree with Richard about this. After my rebuild success I have come across a few pump repairs and even a turbo pump bearing change with a lot more confidence and it was quite worthwhile. In addition the knowledge and tools acquired (that had to be paid for only once) but keep on being useful in the workshop quite often and have "repaid" themselves many time over, for pumps to dishwasher to car repairs etc...

Can't wait to see what performance you get out of it. And, if not to your liking, nothing prevents you to get in there again (should be much faster) to rectify the issue.

Note: should you get acceptable performance don't forget to change the oil after a while to get rid of impurities and metal bits before putting it in regular long term service.
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

Rich and Richard, thank you for your comments. So far I have only spent money on a minor rebuild kit, new motor bearings, power cable, and a few bolts. New vanes cost about $200 so I used the old ones. My dad and I decided we would use the pump to learn. He said the machining would be too hard for me, but we did not talk about using epoxy with metal. I just learned how to use a micrometer. I hope the pump will be ok for something.

Rich, I do not understand your comment. The picture of your stator looks like mine. Does your rotor not have vanes in it? How can you not worry about removing material from the stator? Below is a drawing of one stage of my pump. I will try to explain how I think my pump works later, but the rotor and stator create a seal at the top between the intake and exhaust ports. If I remove material from the stator or rotor the space at the top would get bigger and the oil would no longer seal the two sides. There are 12 areas that have to be sealed. Every edge on the box I have drawn at the bottom of the picture has to have a seal for the pump to work.

Tyler
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IMG_0750.JPG
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

""Rich, I do not understand your comment. The picture of your stator looks like mine. Does your rotor not have vanes in it? How can you not worry about removing material from the stator? Below is a drawing of one stage of my pump.""

Thanks for the drawing. A picture is worth a thousand words indeed. I know understand better how your pump in configured.

I attached a scan of the repair manual and a sketch I did to figure out how long to make the pin to attach to the main shaft. As you can see I have three vanes. They are free to move in the rotor slots and centrifugal force keeps them against the stator wall. If you look at the manual top picture you can see three volumes , "A" left from intake, bottom (B) fully expanded, right venting in the back wall bearing plate (C). Gas is picked up via the intake tube into an increasing large chamber (A) until sealed off by the second vane that forms a second expanding chamber (B). The rotation makes that volume smaller (C) and compresses the gas that escapes though the bearing plate on the side to the second stage. Note that the top 2 vanes takes care of the sealing between (A) and (C).Intake comes in at about 10 to 11 o'clock in the stator wall and exhaust at about 2 o'clock in the back wallplate going to the second stage that from view. In that geometry I do not have to worry too much about a top seal like yours and that is why I was not overly concerned in loosing a small bit of the wall by honing but more worried about the sealing bearing plates clearance on both ends.

The second stage was dirty but not damaged so I figured a slight loss in efficiency in the first stage might not be disastrous.
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notes008 (Medium).jpg
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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman »

Different Rich here. Hard to believe almost eight years have passed, since I worked with any vacuum pumps.

Tyler's drawing reminded me of a perplexing detail in my own scrounged pump, which I took apart for a different problem. This image illustrates the curiosity, and might also serve as a data point for smoothness.

We see that each vane tip touches the chamber wall at only one corner. For one vane it's the leading edge, and for the other vane it's the trailing edge. Had some previous owner assembled the pump with some part backwards?

Turned out, I had fooled myself. The vane tips are symmetric, and the angled contact is just an effect of the eccentric circular geometry. :-)

I wonder if minor pits at oil-sealing places could be mitigated by backing up the rotary pump exhaust with another vacuum pump, for example a little diaphragm pump. That would greatly reduce the "atmospheric" pressure trying to overcome the sealing oil's viscosity, surface tension, and wetting forces. Beware of rotary pump oil being sucked into the backing backing pump.
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Jerry Biehler
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Re: Vacuum pump rebuild

Post by Jerry Biehler »

At that point you are pretty much making the really slow equivalent of a booster pump, also known as a roots blower. They dont rely on good sealing between the lobes and the walls, there is no contact and no oil. They are there to massively move air.
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

That's right...Roots blowers are always the first mover and shaker on giant chambered systems. Then maybe a huge mechanical vacuum pump picks up when the bulk of the viscous flow regime is taken care of by the roots. Days and days are often required to get massive chambers down to the sub micron level. Once down they are kept down with a permanent running to the mechanical pumping system and the secondary deep pumping turbo.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I finished putting everything back together. I attached three vacuum gauges to the intake port and then started the pump. After a few seconds the top gauge was at -29.5 Hg. The thermocouple gauge was at 65 millitorr. The pirani gauge was 49.5 millitorr. The first picture shows the pump running with the pressure gauges. After a few minutes something weird started happening. The pressure started going up and bouncing around. It went as high as 150 millitorr, but it was changing really fast. I started the pump a few times and it did the same thing.

Then something weirder happened. I put my hand over the exhaust port for a second and all of a sudden the pressure really dropped. When I removed my hand the pressure went up and started bouncing around again. I placed my hand on the exhaust port longer and the pirani gauge went as low at 11 millitorr. My dad and I are trying to figure out what might be causing this.

Here is a link to video. https://youtu.be/o6wUOpPbQJs

Tyler
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

If you can hit and maintain 11 millitorr, that would be a win and a most acceptable pump. Good luck in figuring all of this out.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

Just a guess or two:

1)
Leak between the exhaust and the intake?
Can you devise a way to see if atm pressure overtakes an oil seal or a gasket seal or a bearing seal?
The fact that it is intermittent with plugging the exhaust and (I assume) once the pump is warmed up could be due to metal expansion or lower oil viscosity creating that leak. If there is a "pumping" action on the exhaust volume putting your hand on the port gradually lower the pressure (not atm anymore) and if done long enough it will equalise and go the other way to an equilibrium (assuming a better seal than your palm).

2)
again with oil viscosity lower at higher temperature and the pitted condition of the walls and vanes and side walls could it be a loss of pumping action with vane/wall leaking or vane bouncing? Increased pressure building up in the exhaust volume could minimise that behaviour due to the smaller pressure difference? A bit like a Roots pump that although leaky by design will be able to pump large volume of air but will struggle to reach a low vacuum by itself due to all the leaks in the lobes.

Can you easily try a thicker oil to test?

3)
electrical issue affecting the gauge. Pump not grounded, stray current, EMI etc... Try to just touch the pump near the thremocouple and see if it changes. Are these difference of pressure noticeable on the other gauge, if readable?

I am not an authority on vac pumps by any stretch. Perhaps someone on this forum can comment or perhaps you could contact the folks where you got the rebuild kit and they might have experience with that brand of pumps. I was impressed by Duniway support when I had questions doing mine with their kit.

Finally, looking at your setup. The thermocouple gauge is quite close to the intake and can be coated by oil mist that influences its accuracy. This can be cleaned with acetone in mild cases.
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I fixed my pump problem. I installed the wrong valve on the pump exhaust port. I used the metal valve. My dad emailed the company and the metal valve is for a different version. I needed to use the rubber piece with the spring. The pump also had a slow oil leak from the lip seal because I didn’t put it in far enough. I fixed these two things and then ran the pump for an hour. The pressure was 8 millitorr on the pirani gauge. This time the pressure did not change when I put my hand over the exhaust.

The next test is to run the pump for 24 hours and record the pressure. My dad is helping me write my first python program to record the pressure on my PC.

Tyler
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Exhaust valve
Exhaust valve
Lip seal not in far enough
Lip seal not in far enough
richnormand
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Re: Vacuum pump rebuild

Post by richnormand »

Congrats!
If you click with Python there is a very good online course from MIT via the Edx program (assuming you have time).
I would not leave the thermocouple sensor as shown in your previous photo for a 24 h run. Pirani probably OK. I am sure Richard would know.

From your valve geometry was it because the metal valve was leaking too much atmospheric pressure in the internal exhaust port at the exit of the pump?
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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull »

Placing a TC gauge tube right at the inlet to a mechanical pump and letting it run for protracted periods is a bad idea. The only time I recommend this is to determine what you have when you first test your pump. Do not let it run for more than it takes to bottom out the gauge in a couple of minutes. From that point, if the pump needs work or is a piece of junk, never run with the TC gauge tube at the head until some corrective action is taken and you need to see if it has improved.

The TC gauge in my system is about 12" from the pump just before the first conflat valve to the rest of the system. I let the pump run for 2-3 minutes with the valve closed. By this time it is down to 12 microns. I then open the valve to the diff pump and the TC usually rises only slightly but quickly drops back to 12 microns.

Due to my leaky fusor chamber when I open the diff pump to fusor valve, the TC gauge immediately goes to near atmosphere and the pump down continues for about 3 minutes when the entire system, by the TC gauge is below 20 microns.

I only now turn on the power to the fusor chamber's Baratron and the diff pump boiler heater. It can take 5-10 minutes before the diff pump drags the system down into the 10e-4 range. Here is where I can begin fusison.

I have, on two occasions, removed the TC gauge tube and filled it with MEK and shaken it for a minute or two to remove any oil vapor deposits. The fluid comes out clean and clear at 12" from the pump that runs for hours at a time. Once re-installed there is no improvement or decrement noticed in its function from before the cleaning.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Rex Allers
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Re: Vacuum pump rebuild

Post by Rex Allers »

Tyler,

Fantastic work in bringing a very cruddy looking pump back from the dead. Looks great now and your measurements indicate it is working very, very well. You can be proud.

-Rex
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Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

Thanks everyone for all your comments. I ran the pump for 24 hours. I was happy to find the pressure at 9.5E-4 torr on the pirani gauge. The thermocouple gauge was at 0. The pump was very hot when I touched it. I tried a second MKS 901p pirari gauge. It was 2 millitorr after about an hour. I understand the high quality oil in my pump is helping with the low pressure.

The picture below is my finished pump with a few parts left over. The broken plastic parts and magnets in the picture are suppose to be on the motor coupling. The safety valve needs this to work. I removed the safety valve and the anti-suck back valve. These are the other left over parts in the picture. I epoxied over the safety valve hole to the intake port. You can see this in the previous posts. Now I understand how this feature works. I know I need to vent the intake when I turn off the pump. I have a vent valve I will connect outside to replace the parts inside.

Rich, I am not sure about the metal valve issue. I also took the pump body off to fix the lip seal. I tightened the bolts when I put it back together. My dad thinks I should take the pump apart and put the metal valve back in for a test. Then take it apart again and put the spring and rubber valve back. I’m not so sure.

I’m working on a python based vacuum controller so I can log the pressure on my laptop.

Tyler
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Finished pump
Finished pump
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

I tried the metal exhaust valve again. It worked fine. No weird behavior. I then put the spring and rubber exhaust valve back in. It worked the same. Draining the oil and removing the case two times didn’t take too long. I was wrong when I said the metal exhaust valve was causing the weird behavior. Maybe tightening the pump bolts fixed the weirdness I showed in the video.

The first picture is before I removed the exhaust valve. The second picture is with the exhaust valve removed. The third picture is the oil input port. One important thing about how my pump works is how the oil runs through it. The vacuum oil comes in from the outside at the middle of the pump. It exits at the exhaust port. The exhaust port is where both the oil and air leave the second stage of the pump.

Tyler
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Pump with exhaust valve
Pump with exhaust valve
Exhaust valve removed
Exhaust valve removed
Oil input port
Oil input port
Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher »

The first picture is a pump down curve of my vacuum pump. It was taken at the inlet of the pump. There was just the tee and the MKS 901p gauge. It does not take long to get below 10 millitorr. Then my dad had me change the oil with some cheap Amazon oil as an experiment. This is the same oil Samuel used in his thread viewtopic.php?f=10&t=12278. When I started the pump it reached 35 millitorr. After a couple minutes the pressure started climbing. The pressure was over 300 millitorr after 5 minutes. I took off the gauge and put a blank off at the inlet. I am running the pump over night with the ballast open. I will measure the pressure tomorrow. Next I will replace the oil with the good oil to see what happens.

Tyler
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Pump down curve
Pump down curve
cheap oil run
cheap oil run
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