Auto Warz — Fluid Packaging & Carriage Design¶
Document Type: Design Document Version: 0.2 Last Updated: 2026-09-10 Vault destination:
01_Design DocumentsPhase: Phase 1 — Launch release (barrels, tank wagons). Cylinders and the cryogenic rung in the Space Update Related Documents:[07_Pipe & Fluid System Design](<../Systems/07_Pipe & Fluid System Design.md>)·[19_Transport & Logistics](<./19_Transport & Logistics.md>)·[22_Trains & Rail](<./22_Trains & Rail.md>)·[23_Port System Design](<../Systems/23_Port System Design.md>)·[29_Metallurgy & Alternate Recipes Design](<../Systems/29_Metallurgy & Alternate Recipes Design.md>)·[39_Space Layer Design](<../Systems/39_Space Layer Design.md>)·[00_Canonical Design Facts](<../../04_Project Management/00_Canonical Design Facts.md>)Closes: OI-272, OI-278, OI-297, OI-377
Purpose of This Document¶
How fluid leaves the pipe network. Nothing about barrels existed in the vault, and OI-272 flagged why that mattered: barrelling is a lever on the entire fluid story, and done carelessly it either trivialises pipes or is never worth using.
It also turned out to be load-bearing for two other layers. Without packaging, fluid can never leave the planet — the freighter carries cargo, and belts feed the gate.
1. The Principle¶
[19_Transport & Logistics](<./19_Transport & Logistics.md>) §3.2: belts are queues; pipes are pools. So:
A pipe is a pool. A barrel is a parcel.
1.1 The Ambient Rule¶
Decided 2026-09-10. This replaces the framing in v0.1, which asked can the container hold it at temperature. That question was not wrong, but it was the second question, and asking it first left the container ladder open-ended.
What state is the substance in at ambient decides how it travels. That is the moment it is encased, so that is the state the container has to be built for.
| At ambient | Travels as |
|---|---|
| Solid | An ordinary item. No container is involved at all |
| Liquid | A barrel |
| Gas | A cylinder |
Three states, three answers, no judgement call. Everything else in this document follows from it.
Why the earlier framing was superseded. v0.1 correctly observed that molten metal is still a
liquid (fld_liquid_metal has phase = LIQUID), and concluded the container question was purely
about temperature. That let the ladder grow a rung for every temperature band anyone could imagine.
The ambient rule cuts that off: molten metal is a solid at ambient, so it is not container cargo,
and the barrel ladder stops at one rung. What survives of v0.1's point is that temperature is still
the axis a rung moves along. It is just no longer the axis that picks the family.
2. Two Container Families¶
Decided 2026-09-10. Two families, each tiering on temperature range.
| Family | Holds | What a rung buys |
|---|---|---|
| Barrel | Liquids at ambient | Nothing yet. One rung is enough for every Phase 1 liquid |
| Cylinder | Gases at ambient | A wider temperature range, which is how more gas fits in |
2.1 Which fluid needs which¶
| Fluid | Base temp | State at ambient | Travels as |
|---|---|---|---|
fld_coolant |
20°C | Liquid | Barrel |
fld_fuel |
20°C | Liquid | Barrel, and it is flammable |
fld_chemical_solvent |
20°C | Liquid | Barrel, and it is flammable |
fld_liquid_metal |
850°C | Solid | Not container cargo. See §2.3 |
The Insulated Barrel and the Cryogenic Barrel are both deleted. Neither has any cargo under the ambient rule, and a container with no cargo is content that has to be built, taught and balanced for nothing.
- The Insulated Barrel existed to carry Liquid Metal, which §2.3 removes from packaging entirely.
- The Cryogenic Barrel existed to carry Methane and Ammonia in the Space Update. Both are gases at ambient, so they are cylinder cargo. This closes OI-377: the cylinder owns liquefied gases, and there is no second owner to disagree with it.
2.2 Cylinder rungs¶
Gases are the family that actually needs a ladder, because holding a gas colder is how you fit more of it into the same vessel. Rungs widen the temperature range, and pressure rating rides along with it rather than being tracked as a second number the player has to reason about.
| Rung | Carries |
|---|---|
| Cylinder | Ambient gases |
| Reinforced Cylinder | Higher pressure, so more of the same gas per unit |
| Cryogenic Cylinder | Liquefied gases. Methane, Ammonia. (Space Update) |
⚠️ These are named rungs, not "Mk" levels. Canonical §4 makes Mk a building concept: two tracks, applied in place by universal upgrade kits, preserving modules, ports and contents. A cylinder is an item. It has no modules, no ports and nothing for a kit to be applied to. Calling a container "Mk3" would be the fourth time in this vault one word has been given two jobs, and the first person to read it will assume a kit upgrades it in place. Containers tier the way pipes already do: separate items, unlocked by research, crafted individually.
2.3 Molten Metal Is a Local Fluid¶
Decided 2026-09-10. Molten metal is never packaged, and never leaves the planet.
Under the ambient rule this is not a prohibition, it is a consequence: iron at ambient is solid, and
the vault already has its solid form. ref_metal_plate exists, and the decision log's iron gets one
identity line makes smelting an honest SOLID → LIQUID phase change on one substance. Casting is
already in the chain.
You cast it, and you ship the metal. Molten metal exists only between the smelter and the caster.
This is what happens in reality, and the reason is the reason here too. Nobody drums molten metal. Molten cargo travels in one large insulated vessel because the thing that kills it is surface area against thermal mass, and a barrel is the worst possible shape for that: small, many, cooling fast. Where molten cargo does move, it moves by rail in a single big vessel, and only a short distance. Torpedo ladle cars run molten iron from blast furnace to steelworks over a few kilometres, inside one plant or between neighbours. Cooler melts go further precisely because they have less heat to lose. The rule underneath all of it:
How far something can travel molten scales inversely with how hot it is.
Which gives Insulated Pipe a sharper job than it had. It is not "the pipe for the hot fluid", it is the reason smelting and casting have to be neighbours. That is a layout pressure, and layout pressure is what this game is made of.
The one exception is rail, and §4.2 is where it lives.
2.4 Why this does not trivialise pipes¶
OI-272's warning, answered. Packaging does not make pipes optional:
- The throttle is the machines, not the carrier. See §6.
- Molten metal cannot be packaged at all, so the fluid with the most demanding infrastructure is the one packaging cannot touch. Insulated Pipe has no alternative and never gets one.
3. Gases Need a Cylinder, Not a Barrel¶
Answering the decompression question directly: no, reaching another planet needs no decompression step. A sealed container is sealed, and the vacuum outside it does not care.
Adding a pressurise-and-depressurise stage at every planet boundary would be a tax on every route with no decision attached.
The physics behind the family split. A liquid has its own volume: fifty units in a sealed barrel occupy fifty units of space on a landing pad or in hard vacuum, and the wall holds back nothing but the liquid's own vapour pressure, which the barrel already contained the moment it was filled. A gas has no volume of its own. It expands to fill whatever it is in, so the only way to carry a useful quantity is to squeeze it, and that squeeze is the container's purpose.
A barrel is rated for what it holds. A cylinder is rated for how hard it holds it.
[23_Port System Design](<../Systems/23_Port System Design.md>) §5.1 notes that gases travel as FLUID on the pipe network with
phase = GAS. In a container they are a pressure vessel, which is where the pressure question
belongs instead of at the planet boundary.
4. Rail Carries Fluid as Fluid¶
Decided 2026-09-08: there is a tank wagon. A train carriage that holds fluid directly, with no barrelling at either end.
This keeps [19_Transport & Logistics](<./19_Transport & Logistics.md>) §2's rule intact — each carrier owns a different axis:
| Carrier | Moves fluid | Its axis |
|---|---|---|
| Pipe | As fluid | Continuous, local, keeps temperature for free |
| Tank wagon | As fluid | Volume at distance. The only carrier that moves fluid as fluid over distance |
| Barrel / cylinder | As an item | Reach. Anything that carries items: belts, drones, freighters, the gate |
Rail is the only way to move fluid as fluid without a pipe. That is a real fluid advantage for rail, and it does not step on barrels, because rail cannot reach another planet.
The precedent already exists. [22_Trains & Rail](<./22_Trains & Rail.md>) §4.3 gives the Diesel locomotive a fuel
platform with a fuel pipe in, so fluid already arrives at stations by pipe. A tank wagon is the
other half of that plumbing.
4.1 What this deletes¶
The dedicated fluid drone is removed (OI-297). [19_Transport & Logistics](<./19_Transport & Logistics.md>) §3.6 says packaging
is the only way a solid carrier moves a fluid, and a fluid drone would break that rule for no
gain. An ordinary drone carries barrels; rail carries fluid; nothing else needs a special case.
4.2 The Insulated Tank Wagon Is the One Molten Exception¶
Decided 2026-09-10. There is an insulated tank wagon, and it is the only thing in the game that moves molten metal off its own site.
This is the torpedo ladle car, and it survives the deletion in §2.1 for the reason the Insulated Barrel did not: it is one large vessel with real thermal mass, which is the shape molten cargo actually travels in.
Short haul only. The insulated wagon loses heat over distance, and a long run arrives with a solidified load.
That single constraint does a lot of work:
- It makes rail's fluid axis specific rather than generic. Rail does not just move fluid better, it moves the one fluid nothing else can touch.
- It gives a player a real layout choice: centralise smelting and run a short dedicated line to casting, or keep the two together and skip the rail entirely.
- It cannot be stretched into interplanetary shipping, so §2.3's rule holds without needing a separate prohibition. The freighter never carries molten anything, because the wagon it would have to come from cannot reach the pad in time.
How the heat loss is expressed is a data question, not a design one, and sits with OI-376.
5. Tanks Store. Barrels Move.¶
A barrel is not a storage solution.
| Holds | Role | |
|---|---|---|
| Tank | Fluid, in bulk | The fluid store. Unchanged |
| Silo | Filled containers, as items | Storing containers, which is not the same as storing fluid |
| Barrel / cylinder | One parcel | Transport |
A barrel line's endpoints are normally a Tank at each end: fill from the tank, ship, empty into the tank. That keeps the storage system exactly where it was and stops barrels quietly becoming a second, worse tank.
Silos holding filled barrels is still useful — it is how a fluid ends up in a Silo at all, and Silos hold one substance each (Canonical §7), so a Silo of coolant barrels is coherent. It is just not the same mechanism as bulk fluid storage.
6. The Machines Are the Throttle¶
OI-272 asked for barrel capacity to be decided against pipe throughput deliberately. The better answer avoids needing a fudged capacity at all:
A barrel line is throttled by the machines at each end, not by the belt in between.
A barrel line's ceiling is how fast you can fill and empty barrels. That costs:
- Two machines, one filling and one emptying
- Two power draws
- Two footprints
- A return loop for the empties (§7)
A pipe has none of those. So a pipe wins at volume automatically, without balancing a capacity number against a flow rate, and barrels win at reach. Exactly the transport rule that no carrier is an upgrade of another.
This also means container capacity is a free parameter, tunable for feel rather than load-bearing for balance. That is a good place for a number to sit.
7. Barrels Are a Loop, and the Loop Is Lossy¶
Decided 2026-09-08. Empty containers come back.
A barrel line is a loop, not a line.
That makes it a genuine factory problem rather than a belt with extra steps: the return path has to be built, routed and buffered like everything else, and forgetting it is a failure that shows up an hour later as an empty filling machine.
Canonical §12b applies: closed loops are always lossy. Some proportion of containers is lost or damaged per cycle, so a barrel line carries an ongoing steel cost. That is the honest price of using packaging instead of a pipe, and it is a principle the vault already holds rather than a tax invented here.
⚠️ The loop is baseline at every Simulation Level. It is not an opt-in fidelity feature, and §10 says why.
7.1 The recipe shape¶
Per OI-278, and unchanged:
coolant (LIQUID) + empty_barrel (SOLID) → coolant_barrel (SOLID)
coolant_barrel (SOLID) → coolant (LIQUID) + empty_barrel (SOLID)
No special machinery. The relationship lives in the recipe graph like every other production
relationship. A filled barrel is not a liquid in a different form: it is a steel container that
happens to hold liquid, an ordinary SOLID that rides belts for the same reason every other solid
does.
8. Flammable Fluids in Barrels Are a Fire Risk¶
Decided 2026-09-08. fld_fuel and fld_chemical_solvent are flammable, and
[07_Pipe & Fluid System Design](<../Systems/07_Pipe & Fluid System Design.md>) §Flammability already ruptures and ignites pipes near heat.
A belt of fuel barrels running past a smelter is a hazard.
Three reasons it is worth the code:
- It is physically honest, and consistent with the pipe rule rather than a new invention.
- It gives barrels a real downside, so choosing barrels over a pipe is a trade rather than a convenience.
- It makes routing a decision. Where the fuel line runs starts to matter, which is a layout problem.
Note the interaction with §7: a fire on a barrel line destroys the barrels as well as the fluid, so the loss is steel and product together.
9. Barrelling Needs Two Input Media¶
Confirmed 2026-09-08. A barrelling machine takes fluid + empty container, so it needs a FLUID
input port and an ITEM input port on the same building.
That is OI-057, and the good news is that the data model already supports it:
[23_Port System Design](<../Systems/23_Port System Design.md>) §5.1 gives every port its own medium enum of ITEM or FLUID, per
port, not per building.
OI-057 needs confirming, not designing, and containers are the reason to do it now.
10. Simulation Level¶
Decided 2026-09-10. Packaging scales with the session's Simulation Level, per
[19_Transport & Logistics](<./19_Transport & Logistics.md>) §4, and it passes that document's test cleanly: higher levels add
detail to a mechanic, they never change the mechanic. A player packages fluid at every level. What
changes is how much of the physics is their problem.
| Level | Containers |
|---|---|
| 1 | One container per family. A Barrel holds any liquid, a Cylinder any gas. Temperature and pressure are not modelled |
| 2 | Ratings bite. The wrong rung refuses the fill, so the cryogenic and reinforced rungs become required rather than cosmetic |
| 3 | Containers wear and are lost per Canonical §12b, flammable cargo is a fire risk, and a cylinder over its rating vents |
This is a concrete answer to OI-285's strongest candidate, content that only exists higher up: a Level 1 session simply does not model the constraint, which costs no balance tuning at all, because nothing is being made stronger or weaker.
10.1 What must stay baseline¶
The empties loop is baseline at every level. It is not a fidelity feature.
The reason is mechanical rather than aesthetic. §6 shows a pipe beats a barrel line on volume because
of four costs: two machines, two power draws, two footprints and the return loop. Abstract the loop
away at Level 1 and one of the four disappears, which tilts the comparison and makes barrels
strictly better than pipes at that level. That breaks
[19_Transport & Logistics](<./19_Transport & Logistics.md>) §2's rule that no carrier is an upgrade of another, and it breaks it
only at the level new players start on.
Everything else on the table above can scale. The loop cannot.
11. Vocabulary¶
| Term | Meaning |
|---|---|
| Barrel | A steel container holding one parcel of liquid. An ordinary SOLID item when filled |
| Cylinder | A pressure vessel holding gas. Rated for how hard it holds, where a barrel is rated for what it holds |
| Reinforced Cylinder | The high-pressure rung. More gas per unit |
| Cryogenic Cylinder | The cold rung. Space Update, for liquefied gases |
| Tank wagon | A train carriage holding fluid directly. No barrelling at either end |
| Insulated tank wagon | The molten-metal wagon. Short haul only, and the only carrier that moves molten metal off its site |
| Tank | The bulk fluid store. Unchanged, and still the right answer for storing fluid |
Deprecated: fluid drone, removed per §4.1. Insulated Barrel and Cryogenic Barrel, removed per §2.1 — neither has any cargo under the ambient rule.
Open items for this document are tracked in docs/open-items.md, area logistics.
Open Questions¶
- How the insulated tank wagon loses heat — a distance budget, a timer, or a temperature that
decays and solidifies the load below
min_temp. The design constraint is fixed (short haul), the expression is not. OI-376 - Container capacity, which §6 makes a free parameter tunable for feel. Data pass
- The loop loss rate, and whether a lost container simply vanishes or leaves scrap
- Whether a tank wagon can carry gas, which would make it a pressure vessel on bogies rather than a tank. Not needed until the Space Update, and gases riding as cylinders may be answer enough
- Whether the tank wagon needs its own platform type at a station, or reuses the fluid platform the Diesel locomotive already has. OI-378
- How a fire on a barrel line propagates — one barrel, the belt, or the neighbourhood
Revision History¶
| Version | Date | Changes |
|---|---|---|
| 0.2 | 2026-09-10 | The ambient rule, replacing v0.1's can the container hold it at temperature: what state a substance is in at ambient decides how it travels, because that is the moment it is encased. Solid rides as an item, liquid as a barrel, gas as a cylinder. Consequences: the Insulated Barrel and Cryogenic Barrel are both deleted, neither having any cargo left; OI-377 closes, since Methane and Ammonia are gases at ambient and the cylinder owns liquefied gases outright; cylinder rungs widen temperature range, which is how more gas fits in, and they are named rungs rather than "Mk" levels because Canonical §4 makes Mk a building concept and a container is an item. Molten metal becomes a local fluid (§2.3): it is solid at ambient, ref_metal_plate already exists as its shipped form, and Insulated Pipe's job sharpens from the hot pipe to the reason smelting and casting are neighbours. The insulated tank wagon survives as the one molten exception (§4.2), short haul only, on the torpedo-ladle-car precedent: one large vessel with real thermal mass is the shape molten cargo actually travels in, and a drum is the worst one. Simulation Level added (§10) as a concrete answer to OI-285's content that only exists higher up, with the empties loop held baseline at every level because abstracting it away removes one of the four costs that make a pipe beat a barrel line, and breaks the no-carrier-is-an-upgrade rule at the level new players start on. |
| 0.1 | 2026-09-08 | Initial document, closing OI-272, OI-278 and OI-297. A pipe is a pool, a barrel is a parcel. Key correction: molten metal is still a liquid, so the constraint was never is it liquid but can the container hold it at temperature, which makes the system extensible. The container ladder mirrors the pipe ladder — Barrel, Insulated Barrel, Cryogenic Barrel — because it is the same physics; the cryogenic tier has nothing to carry until the Space Update and is specified anyway. Gases go in cylinders, not barrels, which is where the pressure question belongs; no decompression step at a planet boundary, since that would tax every route with no decision attached. Rail carries fluid as fluid in a tank wagon, the only carrier that does so over distance, which keeps rail's axis intact and does not step on barrels since rail cannot reach another planet. The dedicated fluid drone is deleted. Tanks store, barrels move. The machines at each end are the throttle, so a pipe wins at volume automatically and barrel capacity becomes a free parameter. Barrels are a lossy loop per Canonical §12b. Flammable barrels are a fire risk, making routing a decision. Barrelling needs two input media, confirming OI-057, which the port model already supports. |