
Why does a spray bottle work? - otras
https://alexanderellis.github.io/blog/posts/check-valve/
======
vanilla-almond
A few years ago, a British inventor appeared on a TV show called Dragon's Den
(UK version of Shark Tank) and pitched his idea of an improved spray bottle
called the Anyway Spray.

Instead of a normal plastic tube inside a bottle with an opening at the end,
he designed a tube with millions of tiny perforations along its length. This
meant the spray bottle could operate at any angle (even upside down) and could
empty all liquid in a bottle with no leftover.

Here is a 1 min demo of the spray:
[https://vimeo.com/195318537](https://vimeo.com/195318537)

Here's an explanation of how it works
[https://www.youtube.com/watch?v=xXk46rvzdpY](https://www.youtube.com/watch?v=xXk46rvzdpY)

And here's the original pitch he made on Dragon's Den
[https://www.youtube.com/watch?v=RjOvyjeZyIw](https://www.youtube.com/watch?v=RjOvyjeZyIw)

~~~
MichaelApproved
Why isn't this in everything? I'd easily pay an extra few cents to have this
in spray bottles. It's such a frustrating problem.

~~~
chewxy
Here's a cheaper and faster hack: soft tube + weighted end.

The weighted end will tend to go towards where the liquids are. Imagine a
bottle being held lengthwise. The weighted end will be in the same location as
where the liquid is.

Turn the bottle upside down... the weighted end drops to where the top of the
bottle is, along with where the water is.

Standard pressure thingies still work - you still get a spray. No need for
custom membranse.

~~~
exikyut
What cheap alternatives to small bits of metal could be used for the weight?

Metal could interact with and damage a lot of different things.

~~~
mygo
the metal doesn’t need to be exposed to the contents in order to serve its
purpose. It just needs to be on location.. could it not be enclosed by the
same material of the straw?

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SimonSword91
This is a nice example to show the illusion of explanatory depth [0]. Most
people would say they know how a spray bottle works, but fail to describe all
relevant details of the implementation,

[0] [https://www.edge.org/response-
detail/27117](https://www.edge.org/response-detail/27117)

~~~
richardfeynman
Michael Faraday gave a great series of lectures on how candles work that also
illustrates the difference between cursory knowledge and explanatory depth.
Most people think they know how candles work, but when you dive into the
details there are all sorts of interesting things going on.

[https://en.wikipedia.org/wiki/The_Chemical_History_of_a_Cand...](https://en.wikipedia.org/wiki/The_Chemical_History_of_a_Candle)

(you can also buy the lectures in book form on Amazon.)

~~~
fjsolwmv
Engineer Guy (a fantastic YouTube channel for learning how things work) has an
audiovisual curriculum for this book.

[http://www.engineerguy.com/faraday/](http://www.engineerguy.com/faraday/)

~~~
dredmorbius
That is indeed a wonderful recreation of a brilliant original, and I often
think of it when trying to figure out how to _provably and clearly_
demonstrate some _absolutely novel_ concept. Faraday's genius shows through
here.

------
TheSoftwareGuy
One way valves are basically diodes, but for fluids rather than electrons. You
can also make logic gates out of just diodes (or one way valves).

Imagine writing software for a hydraulic computer!

~~~
jetrink
MONIAC [1] was an analog computer designed in 1949 that used water to model
the national economy of the United Kingdom.

1\.
[https://en.wikipedia.org/wiki/MONIAC](https://en.wikipedia.org/wiki/MONIAC)

~~~
digi_owl
Made by an engineer turned economist from New Zealand no less.

Sadly he is better know for a diagram he drew of an observation, the Phillips
curve.

I fear that much like this hydraulic model, Steve Keen's work is likely to be
ignored or ridiculed by future economists while they fret over religious X
diagrams.

~~~
fjsolwmv
Hydraulic models solve differential equations. They aren't bad , but modern
computers are a much better computational environment.

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userbinator
A very simple design, based on a principle that was discovered over 2000 years
ago.

[http://www.mdpi.com/2073-4441/7/9/5031/pdf](http://www.mdpi.com/2073-4441/7/9/5031/pdf)
(see page 13-14)

[https://en.wikipedia.org/wiki/Piston_pump](https://en.wikipedia.org/wiki/Piston_pump)

~~~
maym86
That diagram at the top of the Wikipedia article made the concept more clear
to me than the whole orginal post. Drawing the valves like that really helps.

Edit: grammar

~~~
alanbernstein
That's funny, I don't know what that diagram is trying to convey.

~~~
Stratoscope
Your confusion is understandable, since the Wikipedia article doesn't even
make the slightest attempt to explain the diagram.

So let me try. Let's start with the piston pump on the left. The brown piece
moves up or down in a tube, and the two black "T" figures are valves that open
or close in response to water pressure.

The down arrow next to the piston indicates that the piston is currently
moving down and pushing on the water. This causes the valve at the bottom to
close and the valve on the left to open. So water comes out at the top left.

After the piston is pushed down as far as it will go, you start pulling the
piston back up. This is not shown in the diagram, but now everything is
reversed. The valve at the left closes, and the valve at the bottom opens,
both in response to the pressure change.

So now, water is pulled up from the well or other source, filling the chamber.
When it is full, you start pushing down again, and the cycle begins anew: the
valve on the left opens and the valve on the bottom closes, pushing water out
of the spout at the top left.

Once that makes sense, take a look at the plunger pump on the right side of
the diagram. You will see that it works on exactly the same principle: when
you move the brown part up or down, it pulls or pushes on the water in the
same way as the piston pump. The only difference is in the shape of the moving
part.

~~~
lucb1e
> Your confusion is understandable, since the Wikipedia article doesn't even
> make the slightest attempt to explain the diagram.

A little meta, but in these situations I usually try to improve the source and
post a reply saying I edited it, instead of explaining it to one (or a few)
person(s) here. Not saying it was bad that you just wrote a big comment
explaining it completely! Just an idea of equal effort while reaching more
people :)

~~~
Stratoscope
That's very good advice, thanks for the reminder. I do edit Wikipedia fairly
often, but didn't feel like I had enough time to do a creditable job on this
topic this weekend. So consider my HN comment a rough draft of an upcoming
Wikipedia edit.

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intrasight
What I find most frustrating about the current class of spray bottles is that
they've removed the ability to unscrew the head, and therefore you can't a)
get out the liquid which can't be sprayed, or b) reuse the bottle.

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bitofhope
It's a simple mechanism, but the writing and diagrams deserve an A+ for
clarity.

------
amelius
Wouldn't this design create a vacuum in the reservoir?

Edit: (reservoir = bottle)

~~~
ninkendo
No, because the one-way valve on the bottle end is pointed the other
direction, so that it allows fluid into the reservoir, but not back into the
bottle.

~~~
ninkendo
(Too late to edit: you’re using the terms correctly, I was wrong. I was
thinking of what the article calls the “staging area”)

------
davidkuhta
I found his write-up on MBTA bus mirror positioning to be a short but
interesting read as well: [https://alexanderellis.github.io/blog/posts/mbta-
bus/](https://alexanderellis.github.io/blog/posts/mbta-bus/)

~~~
fireattack
From the map I can't tell how the bus can "go through Bennett Alley and
continue straight into the bus tunnel".

The streets are not aligned, are they?

~~~
otras
Good call! You're right that "continue straight" might not be the best
wording, as they aren't aligned on the map. In real life, they're also not
perfectly aligned, but the entrance area to the tunnel is much wider than
appears on the map, meaning they can take a slight right to continue down the
tunnel. My bet is I was thinking about roads in terms of Boston roads, where
going straight is often more of an abstract concept than a true direction.

Here's a streetview with Bennett Alley on the right and the bus tunnel on the
left if you want to get a feel for the turn:

[https://www.google.com/maps/@42.3731803,-71.1223078,3a,75y,1...](https://www.google.com/maps/@42.3731803,-71.1223078,3a,75y,139.59h,84.47t/data=!3m6!1e1!3m4!1sBV8J62aMITLNkWYsq-
qNRA!2e0!7i13312!8i6656)

Unfortunately you can't see through to the tunnel from the other side of
Bennett [0], but the good news is you can see the 3 buses in action!

[https://www.google.com/maps/@42.3725618,-71.1225705,3a,85.4y...](https://www.google.com/maps/@42.3725618,-71.1225705,3a,85.4y,27.74h,85.66t/data=!3m6!1e1!3m4!1sUtPWI3cNFUs0atO9W-JheQ!2e0!7i13312!8i6656)

~~~
fireattack
Fantastic, thanks!

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anotheryou
How does the nozzle diffuse?

~~~
jstanley
I would guess it's just a fine mesh that the liquid is forced through.

~~~
deltron3030
It's just a hole. If you take a hot needle you can widen the hole of spray
caps and increase the throughput (and size of the throw if you also increase
the distance to the object).

Another trick for spraypaint bottles is to stomp them vertically if you run
out of spraypaint, it won't hurt the system that takes your cap, and gives you
little bit more paint.

------
billsix
Having source be in the "staging area" after "git add" makes more sense to me
now :-)

~~~
jarfil
I think this use of "staging area" comes from the military use, which in turn
comes from the theater "staging", both predating git and the bottle.

~~~
Sharlin
Yep, it’s more likely the author got the ”staging area” from git, as an
analogy familiar to software engineers (or else from the military/theater
context), it’s not an official fluid dynamics term used by spray bottle
engineers. At least I don’t think so :p

~~~
userbinator
Yes, I was a bit bemused by the use of "staging area" and thought the author
was deliberately going for an anachronistic effect, in much the same way that
(computer) machine instructions were called "orders" in the very beginning.

The more common term is just "cylinder".

------
saagarjha
If anyone's curious for more, look up how an atomizer works. It's simpler but
requires more background knowledge (namely, the Bernoulli principle).

------
plaidfuji
I know why I clicked on this; one of my cleaning spray bottles just broke.
What's everyone else's excuse?

------
test6554
I was literally just thinking "how does this work" when looking at a spray
bottle yesterday. Thanks!

------
mirimir
This is cute and all, but still silly. At least, for those of us whose
childhoods included dependence on wells with hand pumps. Or particularly,
responsibility for maintaining said hand pumps. Because it's an ancient
design. Old ones used leather flaps as one-way valves. Same for tire pumps.

------
trumped
The spring might be the reason why a spray bottle doesn't last very long if
you re-fill it with a bleach solution, when it was not designed for it?

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deepdiving12
Great write-up, awesome diagrams, some parts could use some improvement in
language, but the diagrams more than make up for it.

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sbilstein
I would have loved this explained in my high school physics class

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augbog
Clever blog! Design taking apart :) Hope he does more of these!

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bluedino
A clearer title would be, ' _How_ does a spray bottle work'

I'm guessing the authors first language isn't English, but saying 'why' would
be better suited to explaining why a spray bottle works for a certain solution
or process.

 _Why does a spray bottle work well for watering a plant?_

A spray bottle produces many small drops of water which is an effective method
of covering the leaves of a plant.

~~~
otras
Author here, thanks for the feedback! English is indeed my first language, but
I am always looking to improve.

I chose "Why" for reasons similar to what jstanley wrote. When I was first
considering the mechanism, connecting these components by simple tubes seemed
like it wouldn't work. Why then did it work?

 _Why does a spray bottle work [when it seems like it shouldn 't]?_

vs.

 _Why does a spray bottle work [well for watering a plant]?_

I saw that sctb temporarily changed the title to "How", but it looks like
we're back at "Why". I apologize if any readers were expecting a more
metaphysical discussion about spray bottles, but I'd be more than happy to
explore that in a future post!

