History Main / NoFlowPortal

This trope isn't restricted to water, though water is one of the easiest ways to show it in action in fiction. Different atmospheric conditions can be strangely shy about crossing the portal barrier. This is obvious enough with two completely different atmospheres, but for a few [[ViewersAreGeniuses more observant viewers]], this trope may manifest itself in a case where the atmospheres are the same but one is blowing across or even into the portal on one side and having no effect on the other side. What you'd expect to happen in the former is that the air would get sucked through the portal as the wind creates an area of lower pressure in the other world. Even ''sand'' may fall victim to this trope - SandIsWater, for a given definition of 'water' - though in this case the portal is more likely to be just partly submerged in the sand rather than completely smothered by it.

Sometimes, an inexplicably fierce whirlwind sucks in everything on one side of the portal. This is quite common in fantasy works where the portal in question leads to somewhere nefarious and supernatural, though it'll always be less about thermal currents and fluid dynamics and more about [[RuleOfPerception looking impressive]] - how else to make a portal look foreboding and scary?

[[folder:Anime and Manga]]

** [[spoiler:Jadeite's]] portals, don't prevent things on the other side from going through, as shown with the first one seen, where a jet of lava rushes out.
** Underworld Portal installations, don't cause atmosphere exchange between the locations they connect, shown when one connects to a very hot location, from a cool underground dungeon, and the temperature of the destination is only noticed when the portal is exited.

* ''Film/Supergirl1984'': The Binary Chute that leads ComicBook/{{Supergirl}} to Earth opens up at the bottom of Lake Michigan. If it wasn't a No Flow Portal, Argo City would be flooded.

* {{Averted}} in ''LightNovel/GoblinSlayer'', where at one point the protagonist opens a portal to the bottom of the ocean in order to crush a powerful enemy with the resulting blast of water.

[[folder:Web Comics]]

[[folder:Web Originals]]
* Averted in ''WebOriginal/DriftlessWormhole'', one end of the eponymous wormhole is at a higher altitude than the other, and a wind blowing through is the first sign that it's opening.
[[/folder]]

* {{Justified|Trope}} and {{ZigZagg|ingTrope}}ed in ''Film/PacificRim''. It's repeated throughout the movie that humans tried to close the Breach with nuclear weapons but they never worked. This is because the Breach [[spoiler:only opens when it recognizes Kaiju DNA]]. Of course, this doesn't stop other things ([[spoiler:radio signals, the Kaiju HiveMind]], and water of the Pacific Ocean) to flow through the portal at different times in the movie.
* The Binary Chute that leads ''Film/{{Supergirl}}'' to Earth opens up at the bottom of Lake Michigan. If it wasn't to a No Flow Portal, Argo City would be flooded.

* {{Averted}} in ''[[Literature/{{Jumper}} Reflex]]''. The "jumping" teleportation ability that Davy uses actually functions by opening a "Davy-shaped doorway" that moves around him. He develops his jumping ability to the point that he can rapidly teleport between two points and essentially be in two places at once, which keeps the portal open. [[spoiler: Davy uses this in the climax by 'twinning' to the ocean by a nearby beach, flooding the bad guys' facility.]]

The opposite of this trope, naturally, would be where the conditions do affect things on the other side of the portal. A portal which lead straight to a LethalLavaLand, for instance, would be pretty toasty on the other side if ConvectionSchmonvection was done away with. If combined with TimeTravel, this trope's aversion is usually closely allied with SanDimasTime.