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Posted: Thu Apr 24, 2008 12:58 pm
by jimmy101
The tricky part about putting the heating element inside the chamber is that it needs to be elecrically insulated from the water and chamber. I believe Coffee pots and the like don't put the heater wire in direct contact with the liquid. I believe they consist of a resistive heater wrapped around a metal tube.

So, for a resistive heater you need a suitable insulated heating element and a way to get it's electrical contacts into the chamber. And, you probably need a pretty significant amount of power into the heater so it doesn't take all day to heat the system up.

There are the cheapo "coffee cup" immersion heaters. Probably get one at the local K-mart for a couple bucks but it'll probably take a long time to heat your chamber.
http://www.moriluggage.com/Prod-19-1-57 ... Heater.htm
Plus you need a way to plumb it into the chamber.

There are immersion heaters used in chem labs that would work. You might take a look at http://www.hotwatt.com/immersio.htm They have threaded and insulated fittings. Probably not exactly cheap (I don't see any prices on the site).

https://www.coleparmer.com/catalog/prod ... ku=3613600 has various types. The linked one is 100watt for $130. You probably want something bigger than 100W.

:idea:
Perhaps the best and cheapest approach would be to get a replacement hot water heater element from the local hardware store. See for example http://www.plumbingsupply.com/eemaxelements.html. Looks like they run about $50 each. I'm not sure what kind of fitting(s) these heaters have, threaded, compression, ....?

:idea: --- :idea:
Homedespot lists some pretty cheap hot water heater replacement elements. For example, search for SKU 258152;
3500 Watt
240 Volt Screw-In Water Heater Element
Model 15152
$7.97/EA

Most hot water heaters run on 240VAC. I don't know of any reason you couldn't run it at 120VAC, thought the power output will be cut in half.

---------------------

Please be very careful. 120VAC can kill you. Metal + water + 120 VAC is a good way to end up 6' under. In addition, you must have some kind of reliable safety pressure relief in the system.

Posted: Thu Apr 24, 2008 1:10 pm
by biggsauce
It may have been on the Spudtech forums, but there was a member that used a steel pipe nipple for a chamber that lead to a 1" ball valve. He used one set of vice grips to hold the cannon over a propane flame, and another set to operate the ball valve. VERY powerful little cannon.

I know you want an electrical way of heathing your chamber, but you might consider making a metal stand that will hold the cannon horizontal over 1 or more propane torch heads. This way you wouldnt have to hold it to operate the valve and may make it a bit safer (although steam pressure in a closed chamber is pretty serious) rather than taking the additional risk of a water/high voltage electricity mix.

Steam is a sure way to high pressure, but is left to the braver ones such as yourself. Best of luck

Posted: Thu Apr 24, 2008 1:24 pm
by RDX,
Thanks jimmy,
what about getting heating element of deep fryer :idea:
with it I could adjust the heat and even small ones go up to 190Celsius :)
and yes there will be reliable safety pressure relief in my system, and much more safety systems too..I don't want to burn myself with 200C steam.

btw I live in finland so we use 240VAC :D

edit: biggsauce my cannon valve will be activated by electric solenoid valve.. far away :D

Posted: Thu Apr 24, 2008 6:48 pm
by biggsauce
edit: biggsauce my cannon valve will be activated by electric solenoid valve.. far away
Can't blame ya :wink:

Posted: Thu Apr 24, 2008 7:26 pm
by Sticky_Tape
I don't think you should use a solenoid valve they use diaphrams and rubber + high temp. steam = melted diaphram.

Posted: Thu Apr 24, 2008 7:39 pm
by biggsauce
I would imagine he is planning on using a solenoid actuated ball valve...

Correct me if I'm wrong

Posted: Thu Apr 24, 2008 7:44 pm
by DYI
If I'm correct it's a pressure differential triggered burst disk type valve, so the solenoid valve won't be in direct contact with the steam.

You seem to have the heating covered, so here's some advice from my research into steam guns:

Make the gasket for the union out of teflon, it'll survive the temperature in much better condition than rubber would.

Get a pigtail (isolating coil) for the gauge to protect it from direct contact with the steam.

Use more pressure :D

Posted: Thu Apr 24, 2008 7:58 pm
by Sticky_Tape
DYI wrote:If I'm correct it's a pressure differential triggered burst disk type valve, so the solenoid valve won't be in direct contact with the steam.
Oh damn it I forgot how those triggered burst disk things work for a minute but I got it when I first looked at it :oops: .

Posted: Fri Apr 25, 2008 12:55 am
by Lentamentalisk
The real reason why steam works so well is that it is heated so much. If you want real high speed of sound, then use heated helium. Then you dont need to worry about electrically insulating it, so you can get maximum heat transfer at minimal cost. I may give this a try in my upcoming super sonic helium gun...

Posted: Fri Apr 25, 2008 6:23 am
by RDX,
Lentamentalisk wrote:The real reason why steam works so well is that it is heated so much. If you want real high speed of sound, then use heated helium. Then you dont need to worry about electrically insulating it, so you can get maximum heat transfer at minimal cost. I may give this a try in my upcoming super sonic helium gun...
In finland you need licence to by helium, and it costs very much :(

and for the solenoid valve: I´m going to use diaphragm valve that is suitable for steam and high temperatures :wink:

and I will make the gun to be used at 20bars steam pressure :twisted:

and DYI thanks, but I had planned those things already and like I said
I´m going to use copper for gaskets,teflon is little too slippery for use with discs ..

Posted: Fri Apr 25, 2008 11:58 am
by DYI
Why would you need a license to buy helium? It isn't poisonous, flammable, or dangerous in any way other than as a simple asphyxiant. Or do you need a license for any compressed gas tank?

And unless you plan on shooting for speeds over 3 000 fps, there's no point in heating the helium, and the heating would need to be very substantial to gain any real useful improvements.

Posted: Fri Apr 25, 2008 12:52 pm
by Sticky_Tape
I was actually thinking about using heated high pressure helium for a cannon to see if I can get a .177 bb up past the speed of sound I don't have a cronograph but I am thinking I could somewhat prove it by shooting through a steel plate :twisted: that would be cool but I don't have a place I could buy helium :evil:

Posted: Fri Apr 25, 2008 1:17 pm
by DYI
Unless it's complete sh*t, your local compressed gas supply depot should carry helium.

And as I said before, the speed of sound in helium is 3 times that of air. You don't need to heat it or use really high pressure to get a BB over Mach 1, as it's only about 30% the speed of sound in the propellant gas. What's so impressive about hitting Mach 1 anyway? Hypersonic is quite an achievement, but almost any run of the mill handheld projectile weapon is capable of more than 1100 fps.

Posted: Fri Apr 25, 2008 1:28 pm
by Sticky_Tape
because you can say that you got a home made gun to shoot 1400 some odd fps.

Posted: Fri Apr 25, 2008 2:04 pm
by psycix
Ofcourse the sound barrier is a milestone to reach.
Its just an awesome achievement, not many members have yet got it.