vacuum acquired!!

[Q]

while at richard's this last weekend for the heas event, i was able to pick up a nice li'l vacuum station. it's a Vacuum Barrier Corp. model 9005; it's got a Welch 1400 mechanical pump and what looks like a 3" oil diffusion pump, all in one convienent unit. i'm quite pleased with this aquisition
now, does anyone know where i can find documentation for this unit? (the VB website is about useless) perhaps it is as simple as it looks, but i want to make sure that i dont screw it up.
any advice is appriciated.

Q

[Richard Hester]

It sounds identical to a unit I have. Mine has a1400 pulling down on a CVC air-cooled diff pump.

[Q]

hi richard,
yeah, that sounds like the same unit. it's even got some sort of solonoid valve between the two stages, i guess as an isolation valve? perhaps if the mechanical pump fails it shuts the valve...
anyway i'm not very expiranced with vacuum equipment (this is why i STILL haven't finished my fusor ) but thanks to the forum, i am learning. if you can offer any advice on this setup i would greatly appriciate it.

Q

[Roberto Ferrari]

Hi Q,
I have no printed info about that unit, but may give you some general guidelines.
Does the unit has a vacuum meter, with its sensor between the mechanical pump and the diff one? You can use it to diagnostic the system.
-Does the mechanical pump has its fluid? Can you see its colour? Can yo take a sample to see it? It requieres that the oil be clear, not darkened by long use and particles in suspension.
Having a clear oil and a vacuum meter, close the isolation valve and turn only the mechanical pump, watching the meter.
The mechanical pump may have a ballast valve, that you use opening it in order to clean the oil inside. Bubbling air through the oil sweeps away solvents, water and other contaminants. Do this for 15 min.
The mechanical ouput will release a mist, so is safe to run a flexible pipe from the output to the exterior or do it at open sky.
Close the ballast and look the meter. Being the pump in good shape you would reach the lower range in minutes. Not doing so, you can think in many reasons: leaks, dirty oil, valve not closing well, scratched rotor or stator inside the pump. (This one would be the most expensive fix).
In case of getting a good vacuum, stop the pump, let air goes into through the isolation valve and move to the diff pump.
Open it from the upper side, in order to see the deflectors ( a tower of metallic cones). Pay attention of how it is assembled and dissasembly them. The point is to see the botom of the pump and check if it has oil (different one of the mechanical oil) and look for its colour and quantity.
You must to check with the manufacturer about the quantity needed to run it. Usually it is enough to cover the bottom with 1 cm of oil. The oil may be one of several: 704 silicone, poliphenilether, etc.
Oil it if needed and reassembly the diff pump.
Do you have another vacuum meter, with the sensor up stream of the diff pump? It will be mandatory in order to understand if the unit works well.
How it is terminated in the upper side? Just a flange or a valve?
Both pumps works like compressors. Starting alone the mechanical pump and closing the isolation valve you will read in you meter a bad vacuum, and progressively it will improve, until the limit of the mechanical pump.
Having closed the upper side of the diff pump with a valve or chamber, you can start to run it, opening the isolation valve, watching the meter. t
The pressure will rise (bad vacuum) and after evacuating the diff pump will improve to the original levels.
Then you turn on the diff cooling (air or water) and turn on the heater of the diff pump, having closed it at the upper part. (We don't want a rush of air into the hot diff oil).
The sensor between both pumps will help to diagnose the system. First will rise for a while (due to degassing of the diff oil and its walls, etc), then will start to search a stable level. That will also indicate that the diff pump is in its regime. Having a high vacuum sensor at the upper chamber or between the diff pump and a valve, after -say- half an hour, you can turn it and check the high vacuum. May be if you are lucky, you will be in the 10-5 torr order. But... there are virtual and real leaks in the long way to the high vacuum.
Start checking the basics mentioned here and come back with answers and more questions.
Good luck!
Roberto

[Richard Hester]

If I remember correctly, the pump is a CVC VMF-10, and takes 55 ccs of oil. It is a fractionating pump, which means that it is set up to exhaust lower boiling point fractions of the pump oil. It also has internal baffling, which should help prevent backstreaming. I would give the diff pump a good cleaning with isopropanol and acetone, and thereafter use one of the silicone pumping fluids like DC-704 or 705. The Santovac polyphenyl ether pump fluids are even better if you can afford them. The only thing that bugs me about this paticular diffusion pump is the plain tube fittings. This is tolerable for the outlet, but for the inlet, I'd try to use a Cajon o-ring type fitting to transistion to a proper vacuum fitting.

[Q]

richard, roberto
thanks much for the advice. i did check the pump oil, and it is clean but discolored- somewhat of a yellowish color. i guess its old? anyway i will change it before i power it up. i haven't pulled the diff pump apart yet, but plan to do that in the next few days. and yes, the flange on the diff pump is something of a concern. i'm not even sure what kind of flange it is, but i'll work around it some how.

thanks again for your help
Q

[Richard Hester]

It sounds like you may have another implementation of this system. In mine, the connections to the diff pump were made with thick wall vinyl tubing,as the diff pump sports only tubes without any sort of flange If yours is different, maybe a picture would be helpful.

[Q]

ok, there is a heavy vinyl tube between the mechanical pump and the diff, but the inlet of the diff has a short stainless tube with a small flange at the end. i've actually included some pictures this time.
one thing that i am having trouble with is how to get into the diffusion pump. it seems to be a sealed unit. perhaps the pictures will help.

the first is of the whole system, mechanical and diffusion pumps
the second is of the diff pump removed from the vac. station
the third is the flange on the inlet to the diff pump

the diffusion pump does have internal baffles on both inlet and exaust. these ports seem to be the only opening on the pump. everything else is welded. what, do i dump the oil in through one of these ports? i would think that it would render the baffles fairly useless if they were coated with oil.

the more i look at this thing the more questions i have...

Q

[Richard Hester]

I don't recognize the flange, though it should be easy to find an O-ring for it . What is its diameter? If It is close to one of the KF flanges maybe you can fake it...
BTW, the pump does not come apart. The only thing you can take off of it is the heater. You might want to check to see if it still can be removed. One is supposed to use some sort of anti-seize when installing the heater, but not everyboby knows enough to do that. Milk of Magnesia (unflavored) was cited in an old CVC pump data sheet for use as an anti-seize compound.
It is customary to fill the pump through the input port.

[Q]

ah! ok.
yes, the heater is still removable and actually in good shape. slightly discolored from use, but clean. i do like the anti-seize compound citation. i would not have thought of that one.

i'll have to get back to you on the flange- my caliper has gone missing at the moment. a kf rigging might work. i was looking at several vacuum suppliers last night and came to the conclusion that it shouldn't be too difficult to make an adapter for it.

the 'fun' begins...
Q

[DaveC]

There is a type of flange which uses O rings and three or more edge clamps....don't remember the name... could be ISO but not sure about that.

The idea to use a KF flange for the other half could work if you can get a good size match up. Check out all the Vacuum Hdwe suppliers, Norcal, MDC, Duniway, Kurt Lesker, Huntington Labs, online first, though. You can probably find the matching flange.


Also, on pump oils, if they are clear, and pale yellow that sounds like its in good condition. But smell it, too. Used and old oil has a fairly pungent slightly burnt smell. But it never hurts to put in fresh.

Good Luck.

Dave Cooper

[Richard Hester]

The flange shown is probably too small to be an ISO flange. The smallest common one in that series is the ISO63, which is still pretty big. The ISO series also take a captive o-ring, so the grooves look a little different from the simple o-ring groove shown in the picture.
It wouldn't take a whole bunch of effort to machine a custom flat plate flange to mate with the one on the diff pump, if push comes to shove. Using standard ISO claw clamps to hold the two together is a good idea.
As far as the oil in a used vacuum pump is concerned, I would change it as a matter of course, as you don't know where it's been...

[Richard Hull]

Can you pull the "christmas tree" out? That will speak volumes. If it is clean and metal colored you merely need to change the diff pump oil. If it is brown over large areas, then the oil has burned and oxized. Never dismantle a "tree"! Clean it in acetone and dry it well. Bake it in an oven to remove all moisture. Change the oil and re-insert the tree, then bolt the thing up tight to your system. ideally, you will need valves fore and aft of the diff pump to protect it and prevent accidents.

Richard Hull