Pipe networks and pressure

Pipes carry air, exhaust, steam and water between machines. Any pipes that connect form one network with one shared pool, one temperature and one pressure, and everything spatial happens at the edges of a run: where it is produced into, drawn from, vented, or severed by a valve.

The pool

Every pipe segment contributes 30 L of capacity. Pressure is the stored volume divided by that capacity, so a run that holds exactly its capacity reads 1 atm. A gas is compressible and can sit well above 1 atm. Water cannot be packed past capacity, so once a water line is brim full its pressure is whatever the pump commands.

A run carries one medium at a time. The medium is claimed by the first producer and held until the run is empty. Two gases mix; two liquids mix only if they are the same liquid; gas and water never mix. When two networks merge with incompatible contents the larger run wins and the smaller's contents are discarded.

Temperature is one value for the whole run, with no gradient. A gas leak drops it 5 C, and a run holding gas above ambient sheds 2 C per second toward 20 C. The network itself never changes phase: steam becomes water only at a Jet Condenser.

Tiers

This mod ships two pipe tiers. Both are square in section and bolt through flanges, so they connect to each other and to every untiered fitting.

Tier	Bursts above	Passes	Fittings
plated	2.5 atm	50 L/s	none of its own
cast	5.0 atm	120 L/s	valve, pressure valve, outlet, passthrough, passthrough bend

Throughput is a property of the tier, not of the bore. Plated's 50 L/s clears everything the iron tier runs, including a Twin-Tub Blower at 45 L/s, and refuses the steam-tier services above it. The steel tier's rolled pipe is welded rather than flanged and cannot use these fittings at all.

Only a plain segment bursts. Every fitting is exempt, and so is an outlet or a passthrough. The weakest burstable segment in a run sets the ceiling for the whole run, so one plated segment left in a cast line caps that line at 2.5 atm. A run held over its ceiling survives about 30 seconds before its pipes start to fail.

Leaks

Any pipe connector left unconnected bleeds the run: about 8 L/s of gas or 10 L/s of water. What stops a leaking run building pressure is not the loss but a clamp: a producer injecting into a leaking run is capped at 1 atm however hard it is driven. Cap every end against a machine port, a valve or an outlet.

Water evaporates from a sealed pipe or vessel at about 50 L per day.

A joint the two blocks refuse, such as a rolled segment against a cast one, reads as an open end rather than as a hidden wall, so the run leaks there rather than silently merging.

The fittings

Piping (Valve) is a hand-operated shut-off. Right-click toggles it. A closed valve severs the network at that block so the two sides act independently; an open one makes them one run again.

Piping (Pressure Valve) is a one-way overflow between two runs. Nothing passes while the input side stands under the gate pressure; once it is over the gate, the excess crosses to the output side. The gate is dialled in 0.25 atm steps from 0 up to the valve's own material rating of 5 atm, and it defaults to 1 atm. Its input side is the ring with the copper trim, and a wrench flips the direction. With nothing piped to its output it vents the excess to atmosphere.

A pressure valve moves gas downhill only: if the output side is already at or above the input's pressure nothing moves. It is not a check valve, and it does not prevent backflow through the rest of the plumbing.

Pipe Outlet ends a run at a machine's port face. Capped with an ordinary vanilla chimney stood on top of it, it vents the run's gas to the sky at 16 L/s instead, which is the standard way to exhaust a firebox.

Cast Pipe Passthrough (Straight) and its bend, and the plated pair, are lengths of pipe cast into masonry so a wall can be built across a pipe run without opening it.

Fluid Intake draws fresh water from open water into a run. It needs a full cube of water at least 3 blocks deep directly beneath it, and it refuses to work within 6 blocks of another intake.

Step by step: a blast main

1. Set a Twin-Tub Blower on an axle line and give it an axle speed of 1.5 or more.
2. Run Plated Piping (Straight) from the blower to the furnace tuyeres. Straights, bends and junctions snap to face their neighbours as they are placed; a wrench spins one that guessed wrong.
3. End the run against the Tuyere port faces. Every other opening must end at a port, a valve or an outlet.
4. Read the pressure off any pipe in the run. It should settle at or above what the furnace's block info says the burden demands.

What goes wrong

The line sits at 1 atm and will not rise. It is leaking. One unconnected connector anywhere in the run applies the 1 atm clamp to the whole run. Walk it and cap the open end.

The line reads 2.5 atm and the furnace wants more. That is plated pipe's burst rating, and a blower cannot exceed it on purpose. A demand above 2.5 atm means a leaner burden than this tier can blow: charge more fuel, or wait for the steam tier.

Opening a valve dumped the pressure. Opening a valve rejoins two runs, and the pool equalises across both. If one side was empty the whole run reads near zero until the producer refills it.

A freshly placed valve leaks. Open it and close it once.

The pressure valve is spilling the wrong way. It is directional. The copper-trimmed ring is the input. A wrench flips it.

The pipe run is carrying the wrong thing. A run holds one medium until it is empty. Drain it before feeding it something else.