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Fluids in pipes behave weirdly

  • Branch: Live Branch Version: Linux Pending

The physics of fluids in pipes in ONI are really weird, in a way that was super frustrating to me when starting out.


Basically, pipes don't work anything like you'd expect from general knowledge of how liquid works.  Here are some specifics:

  • A single pump can push an infinite amount of fluid.
  • Splitting and then re-joining a pipe will cause the fluid to try to go in circles, even if there is only one source of pressure.
  • It's really hard to understand why fluid does what it does, particularly when it become stuck or goes somewhere unexpected.
  • Passive buildings, like pipe bridges, can somehow "suck" liquid out of pipes without expending energy.
  • Fluid in a pipe can move without any motive force (perpetual motion machine).
  • Fluid in a pipe can "sense" an obstacle far away from it and stop moving.
  • Fluid in a pipe is unaffected by gravity.
  • [nerd complaint] Pressure is measured in mass units rather than force per unit area (?????).
  • [nerd complaint] The energy consumed by a pump (120W) is not nearly enough to move even one "packet" of water at any reasonable speed.


The only mental image I have that explains all this is that pumps actually stuff liquids into small, self-propelled carts which are then loaded into a pipe.  Somehow these carts then move through the pipe (with no source of energy) until they reach their destination, at which point the liquid is unboxed and released.


Why is this a problem?  Because users will do what I did: build a branching pipe network to deliver water from the reservoir.  When this doesn't work, there is no guidance in the game as to how to fix it.  Simple tasks like merging two pipe streams took me dozens of attempts to get right, even consulting online guides.

I think it would be really interesting to see a game like this implement semi-realistic physics for its fluids.  But if that isn't in scope for your plans, the frustration level would IMO be greatly reduced if the system was more understandable and clearly NOT physical -- either by providing more buildings with well defined functions (eg, a set of junctions that define priority so that merging and splitting pipe streams is simpler), or by providing more insight into the decisions made by water as it travels around.


Steps to Reproduce
(1) Be new to the game. (2) Try to build pipes. (3) Get super confused.

User Feedback

I had an incident today which seems to indicate that there is a flaw in how the pipe logic works. Essentially I had a jammed sewage system where my polluted water pipes backed up and refused to flow despite the fact that there was a outlet that would dump water that could not be processed into a large underground storage cavern.


As you can see the red arrows are the expected flows however you'll notice the overflow output is completely empty dispite the entire system being backed up

The issue I discovered was the fertalizer synth it seems when fluid has the potential to move in more than one direction it gets confused and the little fluid nodes go back and forth before getting stuck regardless of wether or not a valid output exists. Disconnecting the synth fixed the issue and allowed flow to resume

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