Using little droplets (beads) of liquid, we can create a percentage based gas pump that moves gases upwards. The principle is very similar to a real life Sprengel pump, just in reverse (thanks @Zarquan). Maybe we should make the name "The reverse Sprengel pump" (comment below on your opinion).
Edit: It's very similar to a "Bubble Pump" which focuses on collecting air below liquid, but instead this pump focuses on forming little "beads" of liquid above a body of air. Both pumps are "air lift" pumps.
This post attempts to explain (1) exactly how this principle works, (2) what it's uses are, (3) how to reproduce the effect reliably, (4) how to control the pump, and (5) some limitations. Of course, I'll aim for extreme case uses that massively exploit this mechanic - as always.
First, some history and credits:
What is a Liquid Bead Gas Pump?
Use liquid mechanics, one-element-per tile, and tile-swapping rules, to cause little beads of liquid to force gas upwards. That's its. These are central mechanics to the game, so probably won't change. I won't call it a bug, rather I'll call it an exploit.
There are probably ways to fix this, but I don't think the devs should focus on this. There are much bigger things to fry.
Why should I care, or How Can I Use This?
The maximum pumping speed has no upper bound (aside from game restrictions on maximum mass, if there are such things). The effective use requires a single gas (multiple gasses can cause problems). The pump can reach vacuum conditions quite quickly. So the uses require single gas settings where speed and/or high pressure are important. Sounds like the steam turbine and gas storage centers are main uses.
The fixed 10kg/s of the steam turbine is no match for the percentage based speed of the bead pump. If the bead pump is not fast enough to keep your turbine(s) running (yes - multiple), then add more steam. Eventually, the pump's speed will overpower any number of turbines (crazy!). While you can provide the required pressure difference for essentially ANY number of turbines with ONE single pump, unfortunately this won't keep them all hot enough (but we have other fun exploits for that - mwhahaha). Here's a few examples
The bead pump can empty a room to vacuum. High pressure storage is quite simple. Should the "liquid over vent" trick ever be fixed, this provides an alternative to unlimited gas storage.
Other uses - I'll add them here as people find them.
Thanks to @Zarquan, we have a simple pump that can suck up 5kg/s CO2 from meteorite impacts, and collect it all in a tiny little room. Quite insane.
How do I form the beads reliably?
The beads automatically form when a liquid, located above another tile of liquid, is forced to move sideways, and then sits atop a layer of gas. This is most easily forced by having the lower tile of liquid being a different heavier liquid, however with a more tricky setup can be accomplished with a single liquid (see this for an example).
Back to the easier setup. Here's a simple setup that guarantees beads, and one that fails to form beads - the difference is the two walls left of the liquids. The second forms solid liquid trails (also fun, but that's another post for another day).
Now the explanation.
Place a heavy liquid (such as crude) in one spot on top of some solid tile (undug, air, regular, normal, door, etc.). Note that this heavy liquid will naturally drain all liquid away except for a small amount. We could call this the "natural minimum" or "overflow" mass. I like to think of it as a measure of the liquid's viscosity - the liquid tends to bunch together in certain minimal size chunks. You can get chunks that are less than this, because of other external effects, but those aren't "natural." For both crude oil and petroleum, this "minimum" mass is somewhere between 350g and 400g. For water and polluted water, this value is between 35 and 40 (a factor of 10 less).
Put a tile on one side of this heavy liquid as well as a tile above that (these are right of the crude and petro above), so things will drain on only one side (this is important). If things drain on both sides, eventually ONI liquid mechanics will displace the heavy liquid and your pump will fail. See the spoiler below.
Put tiles on the other side, leaving a gap for the beads to form. Both tiles are needed. Leave out the top tile, and the beads will disintegrate. Leave out the bottom tile and you might end up with a long liquid trail. Could be fun to use for a new airlock pre-viscogel.
Now add a constant flow of lighter liquid to the tile above this blob (petroleum is lighter than crude - water is lighter than polluted water). The top liquid accumulates mass and then every so often will push the excess liquid sideways. This creates the bead.
Increasing the flow rate causes the beads to form faster, up to a point. This leads to the next section, "How do I control the beads?".
How do I control the beads (i.e. start/stop the gas pump)?
Note, the "overflow" mass discussed in the previous section is important for controlling the speed of the pump. You can quickly estimate this amount by dropping liquid over a single tile and letting the excess flow away. The amount that remains on the tile is this "overflow" or "natural minimum" or "viscosity rating". This natural minimum value depends on the type of liquid, and appears to be independent of any other factor like temperature, surrounding liquids/gases, etc.
To control the speed at which the beads form, you just change the speed at which you drop liquid on the top tile. Valves are perfect for this, though an escher waterfall works too if you need more than 10kg/s to make things work (for example you want to work with liquid metals, magma, or whatever).
To stop the pump, set the valve to zero.
Anything above zero, provided it's large enough to not disappear when leaving the vent, will start to form beads.
You can watch patterns form based on valve settings. Pause the game and look for a pattern such as "bead, gas, gas, gas, bead, gas, gas, bead, gas, gas, gas," If you ever see "gas, gas" in your pattern, then the pump speed can be increased.
Once you hit a little above twice the natural minimum mass (or overflow mass), you'll see the pattern becomes perfectly alternating as "bead, gas, bead, gas, ...". At this point, you've hit maximum speed. The room you are pumping from will reach vacuum, and stay vacuum (though don't 100% trust it will say vacuum, yet). For now, grab the number from the spoiler above, double or triple it, and set the valve to that value. For petro, I used 800 for a while, but once saw gas slip. At 900g, I haven't seen gas slip backwards at all. More testing needed.
To control the height of the pump, there are several options.
Have your pump stop on the floor where you collect the liquid. Simple and easy to setup. Just put the liquid pump (supplying the beads) in the pool on the floor, and let it run. Done. Or let an escher waterfall collect the liquid at high pressure, and use liquid pressure mechanics to send it back up.
Have a gap in solid tiles, on either side of the bead column. What? When a bead forms, it constantly looks on both sides for reasons to unform. If there is a solid non mesh tile next to the bead when it forms, then you can continue building the wall as far down as you want, and watch the bead follow the wall. When you stop building the wall, the bead doesn't disappear. It only disappears when you build another solid tile, at which point the bead disappears and transports to the bottom of the fall in the usual, liquid teleportation, manner.
Let the liquid bead hit a floor, and then teleport for a while without being a bead, and then reform the bead. Do this several times along the downward descent, and you can create multiple pumps, all fed from a single bead setup. This allows you to stack turbines and drain the top region of the turbine to the next turbine's bottom region, keeping the pressure difference quite large. It also allows for infinite gas in a fairly compact environment (the example below can be compacted even more).
What are the limitations?
This list is in the works. Here are a few.
If you try to make the beads form on both sides simultaneously, it's possible for the bottom liquid to get displaced, at which point the whole process stops. Only use one side, and use a tile to prevent the bottom liquid from moving.
Avoid multiple gases. Consistently, you can only guarantee the pump works with a single gas. The pump stops working once you get a blob of gas trapped where the beads should form (and then you have an escher waterfall). Its fun to watch water fall at different speeds with some falling in bead form, and some falling in teleportation mode. The teleported water arrives sooner. I'm sure we can find a way to exploit this too, though I'm not sure right now how (would having liquid arrive in 20kg/0kg/20kg/0kg patterns affect anything in game?).
If you use walls on one side, or both, remember that if you have any gap at all in the wall tiles along the downward decent, then the bead will stop being a bead once you start the wall up again. Gaps in wall tiles are fine, on either or both sides, but once the wall starts again, bye-bye bead. This is both a limitation and a feature.
I'm sure we'll find more limitations, more uses, and we'll find errors in what I wrote above. Have fun playing with this.
Here's my save file with experiments (very early cycles - so quick loading). Viscosity.sav