Have you heard of the Sprengel pump? It’s how they drew hard vacuum back before mechanical pumps were perfected — the first light bulbs had their vacuums drawn with Sprengel pumps, for example. It worked by using droplets of a particular liquid to catch air particles, and push them out a narrow tube, thereby slowly evacuating a chamber. The catch is that that liquid used to be mercury, which isn’t something many of us have on hand in kilogram quantities anymore. [Gabriel Wolffe] had the brainwave that one might substitute modern vacuum pump oil for mercury, and built a pump to test that idea.
Even better, unlike the last (mercury-based) Sprengel pump we saw, [Gabriel] set up his build so that no glassblowing is required. Yes, yes, scientific glassblowing used to be an essential skill taught in every technical college in the world. Nowadays, we’re glad to have a design that lets us solder brass fittings together. Technically you still have to cut an eyedropper, but that’s as complex as the glasswork gets. Being able to circulate oil with a plastic tube and peristaltic pump is great, too.
If you try it, you need to spring for vacuum pump oil. This type of pump is limited in the vacuum it can draw by the vapor pressure of the fluid in use, and just any oil won’t do. Most have vapor pressures far in excess of anything useful. In the old days, only mercury would cut it, but modern chemistry has come up with very stable oils that will do nearly as well.
How well? [Gabriel] isn’t sure; he bottomed out his gauge at 30 inches of Mercury (102 kPa). It may not be any lower than that, but it’s fair to say the pump draws a healthy vacuum without any unhealthy liquid metals. Enough to brew up some tubes, perhaps.
[Helga]: “It’s definitely sucking.”
https://www.youtube.com/watch?v=duUOXmlWk80
(obligatory sucking joke.)
Long time ago my company had strict firewall rules and we couldn’t enter one manufacturer site because “positive suction head” (or similar phrase used on site) clearly indicated “adult content”.
Never mind the questionable soldering — That’s not at all a Sprengel pump.
A Sprengel uses the weight of the fluid in the mercury column to counter atmospheric pressure. It can do this with a column just a meter or two high, due to the density of mercury.
To use vacuum pump oil to make a pump working on the same principle would require a column 14 times higher.
That little peristaltic pump is doing all the work here, not the oil, and especially not gravity. The oil may be helping make an airtight seal in the tube in the pump. But with the correct choice of tubing it would work just as well without the oil.
I’m not sure about that. The peristaltic pump is doing the work in the sense that that’s where the energy is coming from but this build is still using the mechanism of trapping small air bubbles between drops of fluid to pull a high vacuum. That’s what I’ve always understood as the defining characteristic of the Sprengel pump. The source of the power isn’t the main thing. In fact I think you could argue that in original Sprengels the power is really coming from the operator emptying the lower reservoir and refilling the upper one.
No, it’s not ” trapping small air bubbles between drops of fluid”, it’s trapping air bubbles between the lobes of the peristaltic pump. The oil is doing nothing except perhaps helping in the seal, exactly like its role in the vane pump it purports to usurp.
In the video he clearly shows bubbles trapped in the tube before the line gets to the pump.
Let me put it a different way. If the peristaltic pump was replaced with an impeller pump what would you expect to happen? I contend that the device would still succeed in drawing a vacuum as long as the impeller pump is strong enough to keep the fluid flowing. Pockets of gas would still get trapped in the tube line and then get expelled from the vent at the top. What do you think would happen differntly?
There are no “bubbles trapped in the tube”.
The peristaltic pump is moving cavities along, creating a void at its intake. Whatever pressure remains upstream is pushing a mixture of air and oil into that void. Whatever oil is present is coming along for the ride, just like the air. The oil has no function at that point — it’s just dribbled in from the needle valve, mixing with the air flowing from the vessel being evacuated. Droplets of oil in air, or bubbles of air in oil, it makes no difference.
If the pump tubing could maintain a seal (and correct peristaltic pump tubing does), the oil would not have any function at all, and not be required.
The peristaltic pump is already doing that: it’s pinching the tube between two rollers, closing the volume off, forming a “bubble” and moving it along the tube to the exit. The oil is perhaps a good idea so the tube doesn’t stick to itself as it collapses, but otherwise it’s not needed for this kind of a vacuum pump.
The lower limit for pressure with this pump is either a) when the tube collapses on itself from the outside pressure, or b) when enough air diffuses in through the tube (and leaks) that the pump cannot remove it fast enough.
You make a good point. What would the performance be if it were just the peristaltic pump? The oil may be improving it’s efficiency and that in itself is a pretty novel implementation, but this really isn’t operating like a Sprengel pump.
That’s easily tested. Just shut off the oil valve and see what happens. It probably works just the same, though the tube would eventually run dry, and then you need to let in a couple drops of oil again.
As a french guy, I can’t stop laughing each time he says “réservoir”.
I was astounded at first, then Paul mentions it is not a Sprengel pump.
I look again at the design, and if it is true the peristaltic pump is doing the work the design could be much simplified.
Then I rememeber I saw new 2 stage pumps for $75, I have no doubt this cost more.
I’m torn, HaD brought an interesting project to my attention, and the comment section elucidated me, but I feel I need to jump down a rabbit hole now to understand it properly.
Also no mention was made of the useful volume over time, can this evacuate your average test tube or a small vacuum chamber? How long does it take?
The one with the mercury (older HaD link) took several hours to evacuate a bulb size if I remember right. There is probably ways to improve the performance, but idk.
Great video, just had to set the playback speed to 1.5.
Heh, and just yesterday I saw a clip from the Dr. Stone anime about making light bulbs work by drawing out the air using a column of mercury. https://www.youtube.com/watch?v=gR0K7CDzUbk
How is this a sprengel pump?
Those normally need a column that is taller than the distance a vacuum can pull the fluid.
Considering that vacuum oil is slightly lighter than water ( https://www.ravenol.de/en/product/industrieoel/ravenol-vakuumpumpenoel-iso-vg-32 puts it at 0,848 kg/l) you’d need over 10m of column (11.something m for the ravenol).
This contraption seems to not be anywhere near that…
Say you didn’t read previous comments without saying you didn’t read previous comments…
I had wondered about the feasibility of the approach of using oil instead of mercury.
I wonder if it would be possible to use ball bearings to add weight to it to make gravity actually involved. Also, then magnets could be used instead of a pump for control and to move the weight back to the top.
And he chose the wrong pronunciation.
– Pronounce “s” before “p” as “sh”
– “p” as in English
– In Standard German the “r” is formed in the back of the mouth. It’s a bit like using mouthwash, but don’t make your uvula vibrate. In contrast to the English “r” the tongue is mostly flat. The tip and sides of your tongue have to touch your lower teeth.
– “eng” as in “length”
– The second e is pronounced exactly like the first one, but many Germans drop it when speaking fast.
– “l” as in English
Correct pronunciation is not universal.
For example, in the USA France is pronounced FrAAnce.
Not Frounce, as it’s pronounced in France.
Israel same.
Getting the world to roll Rs is going to be a hard sell.
It’s just weird.
Like Berlin and the funny ‘s’.
At least over here the news on tv attempt to pronounce the names of people of our time like the are pronounced in their home country.
It would be funny if they started pronouncing Donald as Dohnuld instead of Donnld tomorrow. We already do that for a certain Disney figure. But I don’t think a certain president would approve of that. In the same way I don’t think a certain pump inventor would have approved of the pronunciation used in the video.
The r in Sprengel isn’t rolled, at least not in the region where he was born. That’s why I wrote that the uvula shouldn’t vibrate.