Passive Vent

The passive vent is the simplest link between a pipe network and the air: you place it on a surface and every tick it mixes the gas in the pipe with the gas in the cell in front of it – instantly and completely. There is no power, no data cable and no setting. You take it down with the wrench.

It brings 100 litres of its own volume, which count towards the pipe network. After that only physics applies: if the pipe holds more pressure than the room, gas flows in, otherwise it flows out, until both sides are equal.

That makes it handy and dangerous at the same time. An example: a room of four cells (32,000 L) at 100 kPa hangs via a passive vent on 20 pipe pieces at 5,000 kPa. Pipe and vent hold 300 litres. After equalising, everything sits at (100 · 32,000 + 5,000 · 300) / 32,300 ≈ 145 kPa. An iron wall only holds a 200 kPa difference – with a full tank on the same network that limit would be passed quickly.

Typical uses:

• Venting exhaust or filter leftovers outside.
• Drawing in outside air, for example on Mars for a filtration unit.
• Keeping two rooms at equal pressure through a short pipe.

The Kit (Passive Vent) also builds a wall passthrough and a version with a valve. An insulated variant that exchanges no heat with its surroundings is the Insulated Passive Vent. If you need a target pressure, use the Active Vent. How pressure and wall limits relate is explained in Atmosphere and pressure.