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Total noob needs advice on the next step.

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Total noob needs advice on the next step.

Unread postAuthor: bullrees » Sun Jan 10, 2010 8:32 pm

First I'd like to say in my first post that I am astonished at the level of knowledge on the website. Very impressive. Anyways..[/asskissing]

After seeing some cool videos on youtube me and my son (9 years old) decided to make our first spud gun. Just so happens the wife was looking for a new oven so off to Home Depot we go.

The oven lady (about 60) and my wife hit it off and started blabbing about whatever so I tell the wife I need a few things and will be back.

Me and my son go and get all the PVC/ball valve....etc and return to the girl-fest in time for the wife to tell me she picked out a 1k oven. My mind was on blasting spuds so i said "whatever you want honey".

Then the wife asks what all the tubes are for and me and my son in unison say"NOTHING". The old oven lady yells "Their making a potato gun" We were stunned the oven lady knew and all the wife could say was "oh god".

We made a simple gun but we want to make it bigger,better,stronger, faster...so what's the next step?

ps: Also would like any tips on how to include a pressure gauge as the home depot didn't seem to have the fittings needed or I didn't know how to incorporate it.

PICS
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Image

Edit:embedded the pics instead of links.
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Last edited by bullrees on Mon Jan 11, 2010 8:36 pm, edited 1 time in total.

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Unread postAuthor: kjjohn » Sun Jan 10, 2010 8:43 pm

First off, get rid of all that duct tape! You did use PVC glue didn't you?

Another thing you could do is make the barrel somewhat longer (longer barrel=more time for gases to accelerate the spud), and use a sprinkler valve instead a ball valve. Have a look at some of the other sprinkler valve guns on the forum to give you some insight. A sprinkler valve can provide I believe up to 50% more power due to the faster opening time, especially if you mod it to run pneumatically with a blowgun. Look up sprinkler valves on the Spudwiki as well.

In terms of the pressure gauge, you could either attach it with fittings, or you could drill and tap a hole in the side of the chamber for it. This involves buying thread taps, however, which can get pricey. I would just order some fittings or go somewhere else to get them.

Welcome to Spudfiles. :)
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Unread postAuthor: inonickname » Sun Jan 10, 2010 8:52 pm

If you tap a hole in the side to mount the gauge ensure you tap it through two layers of PVC.

I think he used glue, as you can see primer stains near the fill valve. Perhaps remove the tape and give it a paintjob.

Is that reducer near the barrel pressure rated? It looks like a bell reducer (which are usually unrated). Make sure it's rated (like the barrel is).

Like Kj said, a longer barrel and more powerful valve will also offer an improvement.
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Unread postAuthor: MrCrowley » Sun Jan 10, 2010 8:53 pm

Is the chamber pressure rated?
Check using this if you don't know how:
http://www.spudfiles.com/spud_wiki/inde ... sure_rated

If the cannon explodes, the duct tape will do nothing so you may as well get rid of it. I also see a bell reducer on the chamber, 90% of the time those aren't pressure rated. Check it with the link I linked above and if it's DWV, get rid of it and build a new cannon.

Don't expect great performance from this cannon, for a first time cannon it's probably better to go with a basic hairspray combustion, you'd get better performance than with this cannon.

The next step would obviously be a sprinkler valved cannon, as stated above, or maybe an advancec combustion cannon with metered propane or MAPP gas, if you feel up to it.

I would probably just put that cannon aside, it probably can take up to 60PSI even if it has DWV on it, but performance will be nothing special at all. If you want to just launch spuds for fun, I'd say go with a basic sprinkler valved cannon or a combustion cannon with metered propane/MAPP.

Any ideas for what you would want to build next?
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Unread postAuthor: hi » Sun Jan 10, 2010 9:20 pm

yep. make the barrel longer and add a pressure gauge.

next step is go have fun, and when you are bored with it upgrade to a modified sprinkler valve.

by the bell-shaped reducer is DWV (drain waste vent) which is intended for exactly that, draining waste and venting fumes. it is NOT designed for pressure. i highly recommend that you get a pressure rated fitting. everything else looks good, but only you know that by checking the actually pipe and fittings. if you are going to shoot it like that and ignore my warning, at least do yourself a favor and keep the thing below 50 psi. even that may not be safe.

if it says nsf-pw its ok to make spud guns out of. it it says dwv, keep moving until you find some that says nsf-pw. its ok if it says dwv AND has a pressure rating.
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Unread postAuthor: bullrees » Mon Jan 11, 2010 5:36 pm

Thanks for the nice welcome and all the great tips, especially about the DWV. I did not know this fitting was not pressure rated. I have fired this many times but only at 40 psi because the neighborhood kids all seem to come out when I take it outside.

Yes I did use primer and glue, the tape was there because I had read somewhere that it may help contain some fragments in the event of a pressure chamber failure. I didn't know if that was true or not but figured it was worth a try for only a few pennies.

I removed the tape to get a better look at the reducer fitting but it has no markings other than the bar code so I am forced to assume it is unrated.The chamber is rated for 260 psi

Image

I think I'll take the advice and just start something new. I have a few ideas but I obviously need to read through the forums more because I have a lot to learn. I'm inclined to stay with pneumatic because I have a compressor and a spare portable air tank that I may be able to use in some way.

Thanks again for all the links, hints and advice. I'm gonna take my time on a new design and post it up for people to pick apart before I start anything.

EDIT:I'll also look into some tap sets, seems like something that will be very useful anyway
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Unread postAuthor: skyjive » Mon Jan 11, 2010 5:47 pm

Yeah that's definitely an unrated fitting. Those are bad news. And I personally prefer pneumatics also, but just go ahead and invest in a sprinkler valve or QEV (Quick Exhaust Valve). They take zero skill as they're premanufactured, and one of those vs. a ball valve is night and day performance-wise.
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Unread postAuthor: bullrees » Mon Jan 11, 2010 6:11 pm

I look at the sprinkler valves every time I go to home depot/lowes but they only seem to carry the smaller diameter (3/4 inch or less) when I look at them. I was under the assumption that bigger is better . I guess it really depends on what you are building so I will take a closer look at my needs with the sprinkler valves and QEV specs in mind.
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Unread postAuthor: spudtyrrant » Mon Jan 11, 2010 6:43 pm

first off welcome to Spudfiles :D

A 3/4 sprinkler valve will outperform the 1 1/2-2" ball valve you have there easily, size isn't everything (I'm sure jsr will beg to differ :roll: ).

An alternative for your next gun would be to make a piston valve, they require some skill but performance is well worth messing up a couple times. here is a link to how they work.

I myself would make a coaxial, since they are easier than other styles of valves to make here is a tutorial for a simple coaxial.
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Unread postAuthor: bullrees » Mon Jan 11, 2010 7:20 pm

I'm gonna take your ideas one at a time so I'm sure I understand. Thanks for the welcome

Piston Valve

Input open and exhaust closed forces the piston forward sealing the barrel and allows the chamber to charge through the equalization hole.

When the chamber is charged, opening the exhaust port causes a pressure difference that forces the piston back allowing the pressure in the chamber to exit the barrel.

Is that the basic idea?

Also does this look more like a reducer that should be used...I know it depends on what is stamped on it but everyone seemed to know right off the one I used was not the right one. Just want to know if I'm on the right track not specifically if this one is acceptable.

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Unread postAuthor: MrCrowley » Mon Jan 11, 2010 7:21 pm

Yup that looks like the reducer, just be sure to check it's pressure rated when you go to buy one.
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Unread postAuthor: bullrees » Mon Jan 11, 2010 7:51 pm

Thanks MrCrowley..I'm on the right track now.

Coaxial Valve

From the animation this seems to be the same concept as piston except the eq tube is a gap around the valve and the barrel is sealed by an additional(smaller diameter) piece of rubber on the face of the valve in respect to the barrel.

Sorry if I'm incorrect or being captain obvious. Just want to be sure I have the concepts right.

Also I'm pretty sure I'm doing something wrong with GGDT. It seems that a spud would do well to fall out of the barrel. I know the lengths are correct but not so much on the diameters and the valve type.



chamber is 3 inch by 25 inch
barrel is 1.5 inch by 20 inch
valve is 1.5 inch ball
I used 57 psig because I have used it at 40 psi and added the ~17 psi for sea level. Not familiar with psig so that may also be wrong.
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Unread postAuthor: MrCrowley » Mon Jan 11, 2010 10:05 pm

Inner Diam should be set to 0.
Inner Diam input is for coaxial cannons (3" chamber with a 1.5" barrel coaxial, Inner Diam would be set to 1.5").

Also you should put pressure at 40PSI, ignore atmospheric pressure.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 12, 2010 12:11 am

spudtyrrant wrote:size isn't everything (I'm sure jsr will beg to differ :roll: )


Au contraire, as someone known for building on the small size JSR is more than happy to agree ;)

Also I'm pretty sure I'm doing something wrong with GGDT. It seems that a spud would do well to fall out of the barrel. I know the lengths are correct but not so much on the diameters and the valve type.


In addition to McC's valid comments, 2.5 milliseconds is a little optimistic as opening time for a standard ball valve ;)
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Unread postAuthor: bullrees » Tue Jan 12, 2010 7:34 pm

Thanks for the tips MrCrowley I'll give it another go.
@ jack yeah 2.5 mil is too fast but I was getting a negative answer already so I wasn't too concerned with that part yet. I'll tweek that when I get a reasonable answer.

EDIT: To my surprise decreasing the speed of the valve gave me a more reasonable answer as jack suggested. I assumed a faster valve would give me a positive result (aka getting out of the barrel) regardless of the other factors.

Looking at it in a new light....a 2.5 ms valve doesn't need a barrel lol.


My main objective with GGDT for now is to simulate what I have(this spud gun) so I can tweak it and see the results.

What is a realistic time for a ball valve 500ms ?
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