Constant pressure concept: aerosols

Threads about how water guns work and other miscellaneous water gun technology threads.
Locked
Jonas
Posts: 4
Joined: Mon Oct 16, 2006 7:25 pm

Constant pressure concept: aerosols

Post by Jonas » Mon Oct 16, 2006 8:25 pm

Something I've come up with when thinking of a constant pressure water gun. Haven't seen an idea like this anywhere so I decided to share it.

Principal:

A fully saturated steam is in a state in which no more liquid can evaporate. into the gas. Steam and liquid find an equilibrium, in which as much say water turns into steam than steam turns into water. The interensting part is that if we squeeze or expand this steam-liquid mixture the pressure stays constant. If you decrease the volume steam will turn into liquid. Increase it and some more liquid evaporates. But p stays constant. I haven't fount a V/p phase diagram on the internet like the 1 in my physics book. The straight line is ss.

The pressure of this system, in which no more liquid can evaporate is determined by the liquid's propeties and temperature. This means that water shot from an "saturated steam" pressure chamber will have exactly throughout the shot as long as there's enough steam inside.

Water is in this state when the temperature is 212 degrees. You do not want to shoot anyone with that and besides it would be impossible to keep the temperature steady. But there are better steams out there: aerosols.


Concept:

basically a sspc water gun would work like pumping water into a spraypaint can, then spraying it out. The water and aerosol would be separated with a piston or balloon, of course so that you don't have to add more. There are a lot of gases to choose from and with p/T tables it wouldn't be that hard to find one which has a good pressure range. Perhaps green gas or red gas, like used in airsoft guns.


benefits:
- Structurally very simple, because you don't need any pressure valves and air tanks for constant pressure.
- a lot lighter, and more compact.

problems:
- the pressure dependant on temperature. If your cannon heats up in the sun it could pop. When selecting a gas you need to take this into account
- how are you going to get enough of that stuff into the pc? You'd probably need to pump it in.
- when you shoot the mixture cools down slightly reducing pressure, and when you pump the mixture warms up increasing the pressure you have to fight against when pumping. This leads to reduced efficiency


note: saturated steam is probably not the official term, just something directly translated from what I have lectures in.

User avatar
SSCBen
Posts: 6449
Joined: Sat Mar 22, 2003 1:00 pm

Post by SSCBen » Mon Oct 16, 2006 9:15 pm

Welcome to Super Soaker Central!

Very interesting idea. I don't suppose it is very practical however unless you have access to aerosols and can afford or carry pipe that can take the temperature. Steel pipe is heavy to the point where it will make your water gun weigh twice as much as it normally would.

I think it would be worth a try however if you do have access to such materials. ;)
Last edited by SSCBen on Mon Oct 16, 2006 9:23 pm, edited 1 time in total.

User avatar
joannaardway
Posts: 855
Joined: Mon Feb 20, 2006 10:04 pm

Post by joannaardway » Mon Oct 16, 2006 10:41 pm

Aerosols use Propane, Butane and other nasties.

Propane usually liquifies at 90 psi, which would mean that you got a constant 90 psi.

It might make for a very good principle if adapted to fit the PCg chamber with the moving piston, but using flammable gasses is highly dangerous.

If you could find a safe gas to do it with, it would be an excellent idea, but using LPG is a definate no-no.

I can't immediately think of a gas that would work, but that's not to say that one doesn't exist.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

User avatar
Silence
Posts: 3825
Joined: Sun Apr 09, 2006 9:01 pm

Post by Silence » Mon Oct 16, 2006 11:50 pm

Neat idea, and while perhaps impractical, it does have potential. Welcome to the forums!

Perhaps brass pipe could be used instead? It might be a good bit lighter, although I can't say for sure.

Jonas
Posts: 4
Joined: Mon Oct 16, 2006 7:25 pm

Post by Jonas » Tue Oct 17, 2006 12:57 pm

Propane shouldn't be that dangerous if you keep it inside a piston with very little air. Famous last words perhaps? At 90 psi it is a bit too high but I think there are some cfcs with more manageable pressure, though they too are flamable.

Evening the temperature would be tricky. Fail at that and the gun is totally non-constant pressure. Placing the brass or steel CPg inside a pvc pipe water tank would help, but then the initially simple design turns into something complicated and heavy.

Flashflood
Posts: 13
Joined: Wed Apr 12, 2006 1:58 am

Post by Flashflood » Tue Oct 17, 2006 10:57 pm

Hey Jonas you show comes on and a little bit. I'm not putting down the show, I love it, you probably love it too. I could talk about the 303rd forever but I'd rather comment on how you are just as smart as your alter ego that comes on tonight in about two hours. It's ironic, no, rather funny, that you are just as smart as The Jonas but yet your'e not. I wonder if there is any correlation. My Tennis coach say, "If you look like a tennis player you'll play like a tennis player" I found that this also relates to water gun battles. When I look like a soldier I act like one. For instance, you usually don't put on a mask and not act like the one that you are impersonating, but you act like the person you impersonate. It's a mental box in a since, you have to think out of the box to not impersonate the person you are imerpersonating. This is my Theory.

User avatar
Silence
Posts: 3825
Joined: Sun Apr 09, 2006 9:01 pm

Post by Silence » Tue Oct 17, 2006 11:20 pm

@ Jonas: True, but the potential for explosion is always there. It's up to the operators' priorities as to safety vs. potential performance. But it's nothing like the danger of a flamethrower.

@ Flashflood: Slightly off topic...

Flashflood
Posts: 13
Joined: Wed Apr 12, 2006 1:58 am

Post by Flashflood » Tue Oct 17, 2006 11:35 pm

With my clues, I wonder if anyone would know what show I am talking about. It is The Unit which comes on in an hour and 20 minuets.

User avatar
Silence
Posts: 3825
Joined: Sun Apr 09, 2006 9:01 pm

Post by Silence » Wed Oct 18, 2006 12:20 am

Yeah, but that wasn't really the topic of discussion. I'm not really into TV, but perhaps somebody else would know. An interesting theory, though.

User avatar
SSCBen
Posts: 6449
Joined: Sat Mar 22, 2003 1:00 pm

Post by SSCBen » Wed Oct 18, 2006 12:37 am

If you want to discuss your favorite TV show, do it in another topic. This thread is for a new CPS idea... not a completely off-topic TV show. I bet that Jonas here doesn't even have any idea about what you're talking about either. :p

User avatar
cantab
Posts: 1492
Joined: Fri Oct 19, 2007 1:35 pm

Re: Constant pressure concept: aerosols

Post by cantab » Mon Jun 16, 2008 5:22 pm

Jonas wrote:I think there are some cfcs with more manageable pressure, though they too are flamable.
CFCs, also known as halons, are NOT at all flammable - indeed, they're used in fire extinguishers!

They are, however, tightly regulated, owing to their ability to destroy the ozone layer, that reduces the amount of skin-cancer-causing ultraviolet radiation reaching the Earth's surface. That's why aerosol spray cans now use propane or butane. I would not recommend you power a water gun with CFCs - it might be illegal if the gas gets vented, and it would also seem inadvisable, when water warfare is best practiced in the sunshine, to make a gun that makes going out in the sun unsafe. (OK it would take a zillion like it to make any noticable difference)

/environmental rant

User avatar
Silence
Posts: 3825
Joined: Sun Apr 09, 2006 9:01 pm

Re: Constant pressure concept: aerosols

Post by Silence » Mon Jun 16, 2008 8:36 pm

I agree. I wouldn't use CFCs or HCFCs on principle, and also because the "it's an insignificant amount" attitude doesn't work when everybody's saying it.

There are some grayish (in ethics, not color) substitutes that are used in dusters and the like. HFC-134 (I think) is used in airsoft and is known to have lower vapor pressure than propane, which has lower vapor pressure than carbon dioxide.

joannaardway also mentioned propane's vapor pressure is around 90 PSI. A chart I looked at said it varies from 110 to 150 PSI as temperature varies from 70 to 90 degrees Fahrenheit. 90 PSI is probably not very common in the summer, depending on where you live.

This is an old thread, but that doesn't really matter.

Locked