Will a Sprengel Pump Work?

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Max Stevens
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Will a Sprengel Pump Work?

Post by Max Stevens » Tue Nov 14, 2017 5:26 pm

The sprengel pump may have been the original high vacuum pump. Apparently, it achieves high vacuum by trapping air in between drops of liquid. When properly designed, a sprengel pump will theoretically pump to the vapor pressure of the liquid used. It looks easy enough to rig for cheap. Such a liquid would usually be mercury, which would pump fast and has a low vapor pressure. However, silicone oil has a lower vapor pressure, and is easy to buy. The problem is that I am not sure if it would pump at all, if not very slowly compared to mercury. Just a few questions: Could it reach the needed vacuum, would the leftover mercury/silicone oil vapor work for plasma without deuterium, and is there be a place to buy mercury?

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Re: Will a Sprengel Pump Work?

Post by John Futter » Tue Nov 14, 2017 5:49 pm

Yes it would work albeit very slowly
The drop tube would have to be very high nearly 30 feet due to the lower density of the fluid
also the viscosity of the oil is going to make it 10 -100 times slower than the mercury version

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Rich Feldman
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Re: Will a Sprengel Pump Work?

Post by Rich Feldman » Tue Nov 14, 2017 8:45 pm

Welcome, Max. Most of your questions aren't hard to answer using Internet searches, and searches of this forum. That includes acquisition of mercury.

John mentioned the tall column required for a Sprengel pump using low-density fluids. A backing pump can greatly reduce the height requirement. I wonder what tube materials aren't wetted by oil? So falling droplets would be like short plugs of mercury in glass, without a film coating the whole I.D. , not that that's necessarily a problem.

One historical article says: The Sprengel pump was so fast and so efficient - Sprengel’s earliest attempts could completely evacuate a half litre vessel in 20 minutes - that everyone working with vacuum used them. William Crookes used the pumps in series in his studies of electric discharges. William Ramsay used them to isolate the noble gases. But, most significantly, Swan and Edison evacuated their new carbon filament lamps with Sprengel pumps. https://www.chemistryworld.com/opinion/ ... 41.article

Chilling the apparatus can reduce the vapor pressure of mercury, from order of 1e-3 torr at room temperature to order of 1e-6 torr at Hg freezing point. Moisture in the gas being pumped would tend to freeze in the pump.
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Re: Will a Sprengel Pump Work?

Post by Silviu Tamasdan » Tue Nov 14, 2017 10:11 pm

You need a liquid that doesn't wet the glass or whatever tube you're using. Else you could make one with any other metal that is liquid at room temperature, such as galinstan. You could make galinstan work, but you need special coatings on the inside of the tubes.

video on building and operating a Sprengel pump: https://www.youtube.com/watch?v=viJ3T-1KZqY
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Re: Will a Sprengel Pump Work?

Post by Max Stevens » Wed Nov 15, 2017 6:25 pm

I just did a little more research, and i found that elemental gallium has an extremely low vapor pressure in liquid form. It is also easily found online. A minor setback would be warming the metal through its cycle, but I could deal with that. It is also about 3/5 the density of mercury, so the pump would maybe even fit indoors!

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Re: Will a Sprengel Pump Work?

Post by Silviu Tamasdan » Wed Nov 15, 2017 6:34 pm

Yes gallium will work if you find a way for it to not wet the glass. As long as it adheres to the glass (and it does it very well) you won't be able to get it to move along the capillary tube.
Same problem with galinstan, which contains gallium and is liquid at room temperature. But it wets glass very well.

(NB there are ways to prevent gallium-to-glass adhesion but I'm not sure they are feasible at amateur level; they involve special coatings of the glass)
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Re: Will a Sprengel Pump Work?

Post by Richard Hull » Thu Nov 16, 2017 7:59 am

If you are really serious about a Sprengel pump, and I mean really serious............Belly up to the bar and use the true, he-man's mercury in it as it was designed. It is the smallest Sprengel pump you can make. If you are going to do it, do it up right and never mind the mercury spill possibilities and the low vapor pressure leaving unseen mercury films all over the place. Man up!

It will help if you have a mercury "still" to warrant absolutely clean mercury for your project. I was offered one for free a few years back. All I had to do was pick it up. You could, of course, make your own Hg still, assuming you can make a Sprengel pump. Where there is a will there is a way.

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Re: Will a Sprengel Pump Work?

Post by Max Stevens » Thu Nov 16, 2017 6:23 pm

I guess I didn't realize that gallium would wet the glass. Thank you for reminding me of that. At this point, I am just doing research on buying mercury in sufficient quantities. I have a furnace that could vaporize mercury already, so distillation wouldn't require much more than tubing and containers. Another acquisition method would be to roast cinnabar and something like zinc in such a distillation apparatus, but at this point, I don't know which method will be cheaper. If I could find my own ore, than home synthesis would be the way to go. However, as far as I have seen, cinnabar is almost the same cost as mercury for what it is worth.

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Rich Feldman
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Re: Will a Sprengel Pump Work?

Post by Rich Feldman » Thu Nov 16, 2017 8:40 pm

There are much easier ways.
ebm.JPG
(kind of overpriced)
ebm2.JPG
(let's watch this one)
I hope those sellers aren't shipping by U.S.P.S., which is against the rules. Other parcel services can transport packages with < 1 pound of mercury, without hazmat documentation & fees.
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Dennis P Brown
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Re: Will a Sprengel Pump Work?

Post by Dennis P Brown » Thu Nov 16, 2017 9:23 pm

Hold on here a minute - mercury being heated? That means a LOT of vapor released (even room temperature mercury releases a significant amount of vapor.) You had better have a good fume hood - mercury vapor is one of the worse substances to breath - over 50% (close to 70%) inhaled remains in your blood stream! It is a powerful neurological toxin and better not have any children breath this vapor.

Tripled distilled is as pure as anyone needs and is available - distilling it yourself is, again, dealing with significant quantities of Hg vapor.

Disposal is an issue - make sure that any company you buy it from allows return for disposal - that is an extremely toxic and hazardous material to dispose of relative to the environment and you must follow all local laws.

That all said, why would you want to create a vacuum using such a primitive system? A cheap, simple diffusion pump using oil is far, far better, and much faster as well as perfectly safe.

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