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Help with Speedivac F203 Diffusion Pump

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Proud Mary

Mon Nov 29 2010, 03:39PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

IntraWinding wrote ...

Thanks folks. For now I'll be thoroughly cleaning and then polishing my diffusion pump and checking out the fusor web site.
I'm guessing that contamination deep within a diffusion pump is less troublesome than at its mouth.
I plan to try it with photocopier fuser silicone oil. It should be pretty low vapour pressure to keep the office workers healthy...

Yes, one often finds that there was some prior state before a later perfected and patented product, which works nearly as well, at a fraction of the cost.

Steve Conner

Mon Nov 29 2010, 04:09PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Before these fancy oils were invented, what they used in diffusion pumps was mercury.

I'm not really sure I see the common ground between a photocopier and a vacuum pump that will make fuser oil work.

I tried to get that paper through the university, but either it's the kind you need to pay for even with an Athens membership, or ScienceDirect isn't playing nice today.

Proud Mary

Mon Nov 29 2010, 04:53PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Steve McConner wrote ...

Before these fancy oils were invented, what they used in diffusion pumps was mercury.

Au contraire, chou-fleur, "fancy" silicone fluids were not the first to be used when the mercury hazard became unacceptable.

Chlorinated hydrocarbons, organic esters, and polynuclear aromatics have all had their day in the sun, but had too much against them
to remain in widespread use. The chlorinated hydrocarbons were toxic, the organic esters were unstable at high temperatures, and so
on.

A succesful diffusion pump fluid should ideally boil without decomposing at around 200Â° - 225Â° C/2E2 Pa, and absorb gases when hot,
dicharging them again during cooling, and not be significantly toxic. Any fluid which meets these broad requirements should at least be considered as a candidate for diffusion pump service.

IntraWinding

Tue Nov 30 2010, 12:06AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

According to Wikipedia,
"most modern diffusion pumps use silicone oil as the working fluid."
and,
"The oil diffusion pump is operated with an oil of low vapour pressure."

Photocopier fusor oil is silicone oil intended to keep the hot fusor rollers lubricated without drying out or poisoning the user, so like diffusion pump silicone oil, it needs to have a low vapour pressure. So there's at least a possibility it's a way to cheaply charge a diffusion pump.
If it works I won't need a mortgage for the 50 cc's of oil this thing need! If it doesn't work I'll just have to clean the pump again. Oh, and I already have a bottle of fusor oil

Thanks for trying for that paper. Here they ask for an Athens/Institution login , which presumably gets you it without further cost

I've discovered that internally the 'Chimney' is just bare copper (after scrubbing the black oxide off), so it looks like the plating on the outside is just for show and my worries about it possibly interacting with the oil are probably unfounded.

Ash Small

Tue Nov 30 2010, 12:16AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'd be very interested to hear how you get on with the photocopier oil, IntraWinding. I've two of these pumps, one has oil it it but I don't know what type (it was originally from the physics labs at Oxford University) the other is brand new, still in the box.

I'm wondering if you can run a foreline pump on this stuff as well.........

Proud Mary

Tue Nov 30 2010, 01:05AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I opened up a few of the old diff pumps lying around here that haven't been used for donkey's years, and some of them had a brownish filmic coating in them that looked like residues of some heavy hydrocarbon fraction. I poured some xylene into one of them and gave it a good shake, and sure enough it took off some of the deposit right away.

I don't know what the pump bore looks like if air has been allowed to get inside while the fluid is boiling, and decomposes. According to Oerlikon, silicone oils are very resistant to this kind of abuse, so it may be that the residue is from some hydrocarbon fluid.

Oerlikon describe their "Diffelen Normal" diff pump oil as "100% Solvent refined Neutral paraffinic oil," so there's no need to limit one's thoughts about it to the silicones alone, especially when the Dow Corning 700 series have such preposterous prices.

IntraWinding

Tue Nov 30 2010, 02:57PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Yes, my guess was most of the black deposit was from oxidised organic oil (the rest, it turned out, was oxidised copper!). I think they refer to this sort of deposit as 'varnish' since the chemistry is similar to the 'drying' of paint.

I'm afraid my projects tend to run over very extended periods, but I'll certainly post my vacuum oil results here. At the moment, for example, the controller for my high vacuum gauge is sitting in a friends cupboard in the US until someone happens to have room in their luggage when they fly over here. I'm still keen to get hold of that paper on different pump oils though - see my original post above.

Any chance you could take some detailed photos of your new F203 so I can see if mines's as it should be? Any idea what the small cylindrical chamber between the pump body and the backing pump connector is for?

As far as using silicone oil in a rotary vacuum pump goes, I suspect it would probably work if the viscosity was similar to the recommended type, but unless you have a free supply it might be more expensive than the usual stuff with the added uncertainty of the effect on the pumps life. I remember seeing perfluorinated oil for rotary vane vacuum pumps and I assume that's one size fits all, so they aren't too fussy.

Ash Small

Tue Nov 30 2010, 03:39PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

The diagram below should help explain it.

It forms part of the fourth stage, it also containd a foreline baffle, and is water cooled on mine as well.

Not sure if mine is exactly the same model as yours (The cover with the serial number is missing), but my second hand one is 350 watt and holds 50 cc of oil.

My new one is only 250 watt with a smaller diameter. It is at the back of the garage so I'll try to dig it out later.

Are you able to post a photo of yours?

Proud Mary

Tue Nov 30 2010, 03:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I've got a shoebox full of ancient Penning and Pirani gauges somemwhere, and the analogue control and read-out units for them, but haven't thought much about them for a while. They are painted in that grey colour favoured by government instrument makers of 50 years ago. They use octal plug-in calibration modules, of which you need to have one for every head. Naturally, the heads I have don't match the calibration modules on the backs of the units, so will need to be adjusted against some absolute standard like a McLeod gauge.

At the moment, these gauges could only be used in a comparative way - i.e. to show that the present vacuum is greater or smaller than some previous state.

Ash Small

Tue Nov 30 2010, 03:57PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

IntraWinding wrote ...

As far as using silicone oil in a rotary vacuum pump goes, I suspect it would probably work if the viscosity was similar to the recommended type, but unless you have a free supply it might be more expensive than the usual stuff with the added uncertainty of the effect on the pumps life. I remember seeing perfluorinated oil for rotary vane vacuum pumps and I assume that's one size fits all, so they aren't too fussy.

The main advantage of using the same oil in both pumps is that if you get any backstreaming from the foreline pump it doesn't contaminate the oil in the diff pump.

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