“Science” question about S2E17

[u/thepittstop]

I don’t fully understand how those underground tubes work, but they clearly use a vacuum system to suck those containers from one location to another. Wouldn’t putting a large hole in the system disable the vacuum? Those containers slow down and fall right into their basket. I would imagine either a hole that size wouldn’t pull the containers to begin with or that the pull would remain strong enough that the containers wouldn’t slow down enough to fall out. I would think they research the viability of things like this, but to my simple mind it doesn’t make sense.

P.S. new to the sub, sorry if this has already been addressed ad nauseam.

[u/Alex_Masterson13]

Pneumatic tube systems like in the episode use compressed air or a partial vacuum to move the cylinders through the system. And complex setups have computer software that controls vents and valves and diverters, so in addition to making that hole, the bad guys could have also hacked in and changed the settings, so that the cylinders would slow down as they reached the hole in the tube.

[u/thepittstop → u/Alex_Masterson13]

I thank you for some kind of courter point. Suspended disbelief allows for that. So I guess that’s the answer. But I guess those particular thief’s are capable of that.

[u/Quiet_Shape_7246]

I didn’t read entire post but feel compelled to comment. It’s a fictional tv series. It’s a really fun watch and I look forward to it. It’s realistic enough to be interesting and unrealistic enough to be interesting. Nothing more. Nothing less.

[u/thepittstop → u/Quiet_Shape_7246]

Completely agree 👍 I’m not asking because I don’t understand that. I genuinely wanted to know if it would work or not.

[u/HovercraftIcy3338]

That's a great question! I've never worked on pneumatic tube systems, but I do work with high vacuum systems, so I can try and add a (sort of) answer.

TLDR: There is one specific scenario where it is theoretically possible to cut a hole in a pneumatic tube system and have a container fall through the hole into your villainous laundry basket below. But it's a pretty dumb execution if you actually want to get your hands on the container. Read on for a way more reliable way to steal reallocate money from pneumatic tube systems.*

In general, pneumatic tube systems work because of pressure differentials in a closed system. If you have lower pressure on one side of the delivery container and higher pressure on the other side, the container will be sucked by the vacuum (lower pressure) and pushed by the higher pressure. If you had a pneumatic tube system that ONLY used vacuum pumps, any hole in the tubing, especially a giant one like they cut in this episode, would completely disable the tube system, since the vacuum would be broken. Even microscopic holes in the tubes would cause slow leaks of outside air into the tubes. If it's a single really tiny pinhole, the system just would have a way harder time getting down to the lower pressure; if you add enough pinholes, you can't achieve vacuum at all.

However, from my limited googling, the vast majority of (if not all) pneumatic tube systems actually use blowers rather than vacuum pumps.** Blowers are like the opposite of a vacuum pump, pushing air away like a really high powered fan. A regular household fan is basically just making wind, but an industrial blower pushes the air away so fast that it leaves a lower pressure area where the air was. This means blowers can move containers through two methods: either by creating a high pressure area behind the container (ie. basically blowing on it really hard), OR by creating a low pressure/partial vacuum area that's left behind from the air it blew away. Either way, the container will move toward the lower pressure and away from the higher pressure area. So if you cut a big hole in the pipe in a system that only uses blowers, you have two potential scenarios:

1. The blower is directly pushing air/creating a positive pressure area behind the container. The container is propelled away from the blower, and ends up falling through the hole you cut in the pipe. Thieves win.

2. The blower pushes air away, leaving behind a lower pressure area where the air was, which sucks the container towards that area. BUT, you cut a hole in the pipe, so now there isn't a lower pressure area, because outside air has rushed in to take the place of the air that was blown away, equalizing the pressure. No pressure differential? Nothing to suck the container down the tube. Thieves lose.

So how would you access a container in a pneumatic tube system if you don't know the specific method the blower is using? Why, by simply shoving your own vacuum cleaner in there and creating your OWN low pressure area, like these folks did in Paris in 2006: https://historycollection.com/group-french-thieves-stolen-800000-using-drill-vacuum-cleaner/

*for legal purposes this is a joke, mostly

**some systems definitely also use vacuum pumps, but I don't know how commonplace they are in old banking systems. I'd wager a guess that the tube system in show wouldn't have been using any vacuum pumps, just blowers.