Diffusion Pump Troubles

[chad ramey]

So..... In the midst of all my deuterium troubles, I am having diffusion pump troubles now. A few nights ago I got my vacuum system(which currently consists of a roughing pump,diffusion pump, and DV-6 TC Gauge) down to around 40 microns with the intent on testing out the diffusion pump. I hooked a temperature probe up to the bottom of the heater and then turned the pump on. Everything operated swimmingly until the heater got up to about 220*F and the pressure spiked to about 225 microns. At first I just thought it was the water in the oil boiling out so I left everything on to see if the pressure would drop after the water boiled out. After about fifteen minutes the temperature was at 350*F and the pressure was still 225 microns. I was talking to Tyler on facebook chat at the time so I told him about the problem. We figured that my oil boils at 416*F so I decided to buy a step up transformer. On Tuesday the transformer came so I hooked it up and tried it out. I started everything up with the same procedure as before (I got the system down to 40microns before I turned the diffusion pump on) and once again, when the pump reached 211-230*F range, the pressure spiked to 225 microns. I decided to wait a little longer and see how high the temperature would go, this time the temperature got up to 600*F but still the pressure was steady at 225 microns.

-I made sure the oil looked clear and there were no black bits to indicate oxidization.
-The step up transformer meets all the voltage,amperage, and wattage needs for my pump.
-The christmas tree is in the pump.
-The pump has the correct amount of fluid charge in it.

Any ideas as to what could be causing these problems?

[Doug Coulter]

1. Bad oil. Try some cheap diffoil 20 from Lesker for starters. Oil does get decomposed.
2. Christmas tree not seated right, so some boiler oil can go "up" instead of through the tree.
3: Oil, like water, has a definite boiling point you can't exceed if there's any liquid left. If you watch the temp vs time temp curve, you should see a flat place at the point boiling starts. If you go above that, it's all vapor and will not pump, but backstream badly. If you don't see a definite boil point plateau,
you've got bad oil.
4: you didn't mention how you are cooling your pump. Most need a goodly water flow or the oil can't condense and you have a boiler, not a pump.
5. Gas type change. If the oil is decomposing, thermal type gages will read higher because they read higher on things like hydrogen for the same pressure.

Run a glow discharge in the tank or in the foreline and watch color, it's a poor man's mass spectrometer and can tell you a lot.

[lutzhoffman]

Hello:

I would start by checking the vacuum gauge over its full range. Next I would check the
coolant flow and connections to make sure that no hoses are kinked ect, while performing a complete external inspection.

Then I would check the christmass tree openings for the top two jets, assuming that the lower one was an ejector stage. If nothing else just to confirm that they are open, and symetrical, to be able to correctly form the vapor jets.

Next I would check to see if the heater was in intimate contact with the DP body to make sure that the heat is getting into the pump, and that there was no air space or other themal barrier. I usually paint on a little Milk of Magnesia on to my heater parts to prevent binding. It just leaves behind a coat of MgO which is refractory and helps prevent corrosion to boot.

Beyond this I cannot think of anything other than maybe a faulty valve if there is one at the HV side. 600 deg. is very hot ! I would not let it get this high again to protect the pump. Also you could try to check the manufacturers we site for a PDF of the instructions for the pump. On my DP I do not usually like to let the backing pump vacuum get under 100 microns, or forepump oil can backstream into the DP. If you have a good foreline trap then this is ok, but I do not, I have a modified water filter with copper wool.

Good Luck.....Lutz Hoffman

[chad ramey]

Doug,

Wow, great idea on the temperature part. I can't believe I didn't think of that, I'm glad you pointed it out to me. I'm going to try and check to see if the tree is making good contact, and add a light dimmer into the electrical system to give me a sort of rough control over the temperature. If I can do that tomorrow after school then I should be able to test tomorrow night and I'll be sure to post my results.

Alas! you found an error in my post, I knew I was forgetting something. For the past few tests I've been blowing compressed air through it I'm probably going to try water this weekend.

Lutz,

I did a rough check of the tree but I'll take a closer look tomorrow.


Thanks for the help,
Chad Ramey

[Richard Hull]

If your mechanical pump is pumping the diff pump to 40 microns and heating the oil forces it to 200+ microns, it is your oil or something in it or something in crud locked in the pump that outgases with heat. It would not be a mis-set tree or anything like that. Another item might be a micro-crack or a leak in the pump, a weld joint, gasketing, boiler or its body that is opening (expanding) with heat.

Richard Hull

[DaveC]

Chad -

Don't know what size your pump is, but if it IS water cooled, you'll need something in the range of a liter/minto a gallon/min....arm waving estimates, of course.

No cooling was my first thought, but Richard and Doug have mentioned several more condidates.... a high temperature vacuum leak somewhere in the pump body is a real possibility.

If your oil is clean in appearance, I'd go first with it being okay... maybe not great but probably usable.

With the diif pump actually working, you should be able to see the glow extinguish, with a kV or two on some electrodes.

Good luck.

Dave Cooper

[chad ramey]

Richard,

I'm led to think it might be something with the oil other than the problem being from a leak. I think this because when I got home today, I poured the oil from the first pump into another diff pump that I had laying around and tried everything again with the same results.

Thanks,
Chad

[chad ramey]

Well Gents, I have returned from the garage to tell of an epic battle! It took a gasoline leaf blower and copious amounts of compressed air, but I got the neck of the diffusion pump cooled down and watched the pressure plummet. With the diff pump running, I got the vacuum system down to 1 micron! Tomorrow I'm going to go to home depot to pickup all the fittings necessary to build a water cooling system powered off of my garden hose. My only question is, will a garden hose provide sufficient flow to cool the pump?

I really appreciate all the ideas and help,
Chad Ramey

[Chris Seyfert]

That sounds like an epic battle indeed! I'm surprised you managed to make a water-cooled diff pump work at all without the water supply.

A garden hose will provide more than enough cooling. Buy yourself a nice valve, you'll need it for throttling the flow rate. I don't know what size diff pump you have, but I've run Varian VHS-4 size pumps at my work, and they work fine with a 1/4" OD plastic water line, running a soft stream such that the water exit temp is comfortably warm to the hand. By spec, a VHS-4 requires 0.15 gpm (30 L/hr) flow rate, and that's with a 1450 watt heater.


Bottom line is, as long as the exit water is mildly warm, it's enough flow.

[Jerry Biehler]

I have a 6" Technic pump that is water cooled. It wants, I think, .5 gpm. I use something like a TIG cooler to cool it and I am getting down to below 2x10^-10 (X-ray limit) in my chamber using Vacoil S. I have played with the flow amount and it seems to be as long as the walls of the pump are cool it will pump well. If you do run a recirc system make sure you put something in there to stop bacteria growth. I had enough growth in a week or so to plug up the filter in my pump. Or use RO or distilled water.

When I first turned on the pump with its original oil it did outgas quite a bit getting all the absorbed crud out of the oil.

[Tyler Christensen]

If a closed loop is used I'd suggest using a little anti-freeze for bacteria growth stopping even if using distilled, stuff still gets in from my experience. I've put a little in my computers closed cooling loop and haven't had any growth problems for over a year on the same water charge. And obviously it won't cause problems with decaying pipes or anything since it's designed for that use.

[chad ramey]

Once again, thanks for all the help guys!
Chris and Jerry, thanks for the information on the flow rates and different cooling system designs.
I'll be sure to start a new post tomorrow with pictures of the cooling system and results on how it does.


-Chad Ramey

[DaveC]

Chad - If you use some copper tubing (1/4" dia. soft copper) as part of the water circulation system, you will have little or no algae growth problems. I have a closed system that is open to the air, and after several years of operation, it has remained growth free. It's the copper biocide action that does it.

An occasional vinegar rinse is what I have to do because of the lime in the water. But otherwise...that's it. Bleach also works nicely as an occasional flush.


Dave Cooper

[Jerry Biehler]

All the cooling lines in my system are copper and I got diatoms in no time flat. Maybe you have more acidic water than I do and its pulling some of the copper ions from the tube. Maybe add a touch of copper sulfate. They use that as an algaecide in stock ponds.

Copper is a great way to kill diatoms, algae, and other microorganisms. I used to do salt water reef tanks and possible copper content was always something to be aware of.
Dave Cooper wrote:

[Richard Hull]

We can now add plumbing to the list of requisite technologies needed for fusor operation.

Who'd a thunk it?

Good luck to all non air cooled diff pumpers.

Richard Hull

[Jerry Biehler]

Easiest solution for water cooled diff pumps to get the needed flow rate is a carbonator pump. These can be had from any restaurant supply store that deals with used equipment. I got a pump/motor with a 1 gallon stainless tank for $50. Add a small radiator or automotive heater core with a 5" fan attached to it and you are ready to go. Flow should be from the pump to the diff pump and then through the radiator and back to the tank. The small radiator and fan units that overclockers use to water cool their computers will work fine.

Almost all carbonators (and tig coolers) use Procon pumps. They are a direct drive graphite vane pump. Pressure output is adjusted by removing an acorn not adjacent to the intake of the pump. There is a screw that adjust the tension of the spring on the bypass valve. Loosening it lowers the pressure, tightening it raises it. Many carbonators are set to 125PSI which is way too much. You may have to cut off a loop off the spring to be able to get it down to the 50 to 60 PSI that you really want.

Do not try to run a setup like this without a radiator! The pump heats the water enough in a closed look that you can soften vinyl hoses.

I have worked on many, many TIG machines (I am a certified Miller repair tech) and the main way things go wrong is diatom growth in the water. This will plug the filter in the pump. There is a screen filter that is accessible under the larger Acorn nut that can be cleaned out. In reality with clean water in a recirculating system you can leave this filter out.

Note that the above recipe for a water cooler is perfect for a tig cooler as well. TIG torches and water cooled diff pumps like the same conditions.

[Carl Willis]

I too like the Procon pumps. A centrifugal pump will work also, but needs a bypass leg on small loads like a diff pump.

A soluble chrome(VI) salt (chromate / dichromate) ought to put the diatoms and anything else living out of business with a quickness. I have not put anything in my water in the past, though; just changed the water on occasion when slime started to show up on the walls.

[lutzhoffman]

Hello:

I know lasers are not diffusion pumps, but they depend on de-ionized water and they suffer horrible problems from any bio based growth. The plumbing on lasers is SS and polymer, with some brass. The standard industry laser cooling system "flush" chemical that is used to clean and disinfect them is Hydrogen Peroxide, at at least 10-15% concentration. I still have some 30% H2O2 which I use for my Nd:YAG laser. I have been told that you can get 15%+ H2O2 at pool supply places, also one non chlorine bleach product at Wallmart is basicaly H2O2. I have not tried these since I still have some 30%.

It also makes a great replacement for bleach at home because it does not form highly toxic dioxins, and organochlorine compounds when it hits organic material like your kitchen surfaces. The wife will appreciate this if you tell her, especialy given that these organo-chlorine compounds cause endometriosis and other female problems in women.

I have also used this on my HS-2 with no problems, H2O2 kills anything biological in the system, and it leaves no residue behind. Most metals tollerate it very well, as do polymers, just remember to flush it out.

Take Care....Lutz

[Carl Willis]

Hi Lutz,

The 25+% peroxide sold in my local pool stores is called "Baquacil." It comes in a purple gallon jug that costs about $14 and leaves big white burns on bare skin. Wonderful stuff.

-Carl

[Jerry Biehler]

Another source of concentrated H2O2 is beauty supply places. The professional type. Supposedly up to 40%.

A friend of mine works on LASIK machines and used to work for ESI. He still works on ESI YAGs part time. Ill have to ask him what he uses.

[derekm]

Tyler Christensen wrote:
> If a closed loop is used I'd suggest using a little anti-freeze for bacteria growth stopping even if using distilled, stuff still gets in from my experience. I've put a little in my computers closed cooling loop and haven't had any growth problems for over a year on the same water charge. And obviously it won't cause problems with decaying pipes or anything since it's designed for that use.

and you have it your Garage -- oops but people dont fix cars anymore or even top up the coolant.

[lutzhoffman]

Thanks for the tip on the Baquacil, 25% is great, it will do very nicely. For a bit of true dark humor:

My friend had a jug of 35% H2O2 sitting in the basement, his dad grabbed it to "disinfect" a sore on his dogs anal area, needless to say he was not a happy camper. I would advise everyone to put a dilution warning label on this stuff, in my friends case it ended in just a few yelps, and some jumping around, but it could have been more serious, wear gloves to.

I wonder if the 25% stuff will work as a mono propellent for catalyst based rockets? I suppose you could concentrate it a little if you are real careful.

Thanks for the tip.......Lutz : )

[Richard Hester]

Lutz -
It's a wonder the poor put-upon dog didn't bite the applicator of said peroxide.

Everyone else -

If you read some of the pages regarding the old ME-262, which used peroxide as an oxidizer, remarks were made regarding the destructive nature of pure peroxide on human flesh. Also, since peroxide is used to make peroxyacetone, which is an explosive used by terrorists on the cheap, do not be surprised if you get some official attention if you buy a lot. A bit of copper sulfate might work as well.

[Doug Coulter]

The so called "40 volume" stuff they sell, is about 12% H2O2 and will take the skin right off you as well.
I happened to be dating a beautician at one time, she filled me and and got me some, without me having to go to Gitmo for getting a goodly amount.

[derekm]

Me163 not Me262

Me262 twin turbojet

Me163 Komet - rocket propelled - mostly hydrazine and H202

T - stoff 80% concentrated hydrogen peroxide / 20% oxyquinoline
C -stoff Hydrazine methanol & catalyst