Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 74 users online :: 5 registered, 0 hidden and 69 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Rastamuffin Has Performance Problems

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.
Sponsored 
  • Author
    Message

Rastamuffin Has Performance Problems

Unread postAuthor: rastamuffin » Sun Jan 18, 2009 12:19 am

I made a very simple spudzooka for airsofting purposes a 3ft tank made out of PVC connected to a ball valve and a 2 ft barrel all made out off pvc andd glued with pvc glue. Its very airtight no pressure loss at 100 psi for 45 min i left it there and it was still at 100 psi. The problem is when i fire anything out of it...even at 140 psi it doesnt go very far. I dont know why. I wad it up good and i have used beanie babies, bags of bbs and rubber balls as ammo and it all falls at 40 ft and i dont know why can u guys help?

thanks in advance
  • 0


rastamuffin
Private
Private
 
Posts: 15
Joined: Sat Dec 06, 2008 4:26 pm
Reputation: 0

Unread postAuthor: Insomniac » Sun Jan 18, 2009 12:32 am

Well for starters, the ball valve is far from the best you could be using. Try opening it as fast as possible and see if that increases range. Also, are your projectiles nearly airtight/slide in the barrel easily.
  • 0

I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

Add me on msn!!! insomniac-55@hotmail.com
User avatar
Insomniac
Major General
Major General
 
Posts: 1297
Joined: Mon Dec 18, 2006 3:47 pm
Location: Australia
Country: Australia (au)
Reputation: 0

Unread postAuthor: starman » Sun Jan 18, 2009 12:48 am

How big is your ball valve?
  • 0

User avatar
starman
Donating Moderator
Donating Moderator
 
Posts: 3041
Joined: Wed Dec 12, 2007 12:45 am
Location: Simpsonville, SC
Reputation: 0

Unread postAuthor: jook13 » Sun Jan 18, 2009 12:58 am

As the others have hinted at, we could do a lot better of a job with helping if we get some specifics. What diameter is the air tank and barrel? Try a heavier ammo, like a golfball with wadding behind it (depending on the bore of course...)

Also as mentioned before, a ball valve is less than ideal to say the least. If you feel like taking the next step, search this forum for a bit and look into a sprinkler valve and how to mod it. If you are feeling frisky, look into creating your own piston valve.
  • 0

I like to play blackjack. I'm not addicted to gambling, I'm addicted to sitting in a semi-circle.
User avatar
jook13
Lieutenant Colonel
Lieutenant Colonel
 
Posts: 434
Joined: Mon Jan 21, 2008 10:39 pm
Location: Prescott Arizona
Reputation: 0

Unread postAuthor: SpudsMcGee » Sun Jan 18, 2009 12:58 am

Like starman is implying, depending on the size of the valve, the amount of air hitting the projectile is vastly different. I have a little spud gun that uses a ball valve and how fast you open the valve really changes the distance you will get.
  • 0

(\_/)
(o.o)
(><)

Current Project: Slasher Valve
User avatar
SpudsMcGee
Master Sergeant
Master Sergeant
 
Posts: 160
Joined: Mon Nov 10, 2008 10:03 pm
Reputation: 0

Unread postAuthor: john bunsenburner » Sun Jan 18, 2009 1:38 am

Assuming your barrel and chamber have the same diameter then you have a C:B ratio of 3:2, far from the recomended 0.7:1. In other words, if my have a big chamber like that then make a longer barel for it too. The ball valve has also beein pointed out so there is no need to discuss it.
  • 0

"Did you ever stop to think that out of the seven deadly sins envy is the only one which doesn't give the sinner even momentary pleasure"-George Will
User avatar
john bunsenburner
Major General
Major General
 
Posts: 1446
Joined: Sun Oct 19, 2008 5:13 am
Reputation: 0

Unread postAuthor: rastamuffin » Sun Jan 18, 2009 10:41 am

Yes all the pvc includeing the ball valve is 2 in around. I have used heavy projectiles and wadding. One time i smashed a spud into the barrel shaving off some of it as it went in and it got much better range then anything else ive fired. Then again i also used a rubber ball which just barely went in it was so tight and it came out with a bang but not much range
  • 0


rastamuffin
Private
Private
 
Posts: 15
Joined: Sat Dec 06, 2008 4:26 pm
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: Ragnarok » Sun Jan 18, 2009 11:20 am

john bunsenburner wrote:Assuming your barrel and chamber have the same diameter then you have a C:B ratio of 3:2, far from the recommended 0.7:1

Two errors here - firstly, there is no such thing as a 3:2 C:B ratio - it's 1.5:1, it has to be divided back fully so that the barrel half of the ratio is equal to 1.

Also, the 0.7:1 or thereabouts is for atmospheric combustions.
There is no single "recommended" pneumatic ratio, but personally I would advise being between 0.5:1 and 2:1. Less than that, and you're limiting power. More than that and you're wasting efficiency for little gain.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: jrrdw » Sun Jan 18, 2009 11:53 am

Here's the back yard version of what Ragnorok said = You want the chamber to be twice the size of the barrel by volume. Get a faster opening valve. You can adapt down to a 1 inch modded sprinkler valve and back up to a bigger barrel if you sabot you projectile right. A slight drag all the way down the barrel and positive seal is best, in my opinion.

Using a faster opening valve will make a world of differance. :wink:

Welcome to Spudfiles. :D
  • 0

When life gives you lemons...throw them back they suck!
User avatar
jrrdw
Donating Moderator
Donating Moderator
 
Posts: 6538
Joined: Wed Nov 16, 2005 5:11 pm
Location: Maryland
Country: United States (us)
Reputation: 25

Unread postAuthor: rastamuffin » Sun Jan 18, 2009 2:06 pm

right now i cant make a bigger chamber so what can i do with what i have to work with in terms of ammo :(
  • 0


rastamuffin
Private
Private
 
Posts: 15
Joined: Sat Dec 06, 2008 4:26 pm
Reputation: 0

Unread postAuthor: starman » Sun Jan 18, 2009 2:22 pm

A tight rubber ball will be limited in range by friction in the barrel. Potatos work well because while they fit snugly also slide relatively easily back out of the barrel.

Find hard ammo, lightly sabot'd if needed. A 2" ball valve is a monster and typically difficult to operate. A little vasoline around the ball will free it up some. There's also the option of extended the lever some allowing you to apply more force when opening it.
  • 0

Last edited by starman on Sun Jan 18, 2009 4:54 pm, edited 1 time in total.
User avatar
starman
Donating Moderator
Donating Moderator
 
Posts: 3041
Joined: Wed Dec 12, 2007 12:45 am
Location: Simpsonville, SC
Reputation: 0

Unread postAuthor: Ragnarok » Sun Jan 18, 2009 2:30 pm

rastamuffin wrote:right now i cant make a bigger chamber so what can i do with what i have to work with in terms of ammo :(

In this case, I wouldn't exactly recommend a bigger chamber. In your case, as your barrel is so short and you're using a slow valve, it would actually be far better to extend that instead.
Your short barrel and slow valve are the source of your problem.

For most barrels, pressures and projectiles, after triggering, figure the projectile is in there for a a couple of dozen (or thereabouts) milliseconds - the shorter the barrel, the less time (obviously).
With a ball valve it will take you of the order of ten times longer than that to get the valve fully open. In an ideal world, you want the exact opposite - you want the valve opening in no more than about a tenth of the time the time the projectile is in the barrel, else you're losing power.

For an analogy, using a ball valve on a cannon is about as effective as using a sieve to transport water - very little of what you originally fill it with (be that water, or pressure) will make it to where you want it to go (in the case of the cannon, this would the energy in the compressed air being transferred to the projectile).

You want as much of that pressure to give it's energy into the the projectile. A ball valve just means that large amounts of the air you put into the launcher will never be used.

In other words, you're gonna need a bigger boa... I mean, a bigger (that is to say, longer) barrel.
Not to mention a faster valve.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: rastamuffin » Sun Jan 18, 2009 2:33 pm

so if i put a levver on the valve to open faster would it be better? and how do i make a nice round like sabot or somethin can u guys give me a link to a video im using this for airsoft keep in mind i want to have bbs at a certain point spread like an explosion...im sorry bout being such a n00b
  • 0


rastamuffin
Private
Private
 
Posts: 15
Joined: Sat Dec 06, 2008 4:26 pm
Reputation: 0

Unread postAuthor: jrrdw » Sun Jan 18, 2009 3:11 pm

Styrofoam works well, easy to cut, light weight. Make a 2" piece, hollow it out enough for a load of shot, cut it in half. Preload it, shove it down the barrel. Experiment with what ever you can find and think of. :D
  • 0

When life gives you lemons...throw them back they suck!
User avatar
jrrdw
Donating Moderator
Donating Moderator
 
Posts: 6538
Joined: Wed Nov 16, 2005 5:11 pm
Location: Maryland
Country: United States (us)
Reputation: 25

Unread postAuthor: Ragnarok » Sun Jan 18, 2009 3:31 pm

rastamuffin wrote:so if i put a levver on the valve to open faster would it be better?

Perhaps. When I was still using them as main valves, I generally either added a lever, then some kind of pull string to the end of that lever - or sprung loaded them.

These days the only time I'd ever really consider a ball valve on a cannon is where it's opening time is irrelevant and where it's full bore flow is important - like when I'm adding my "safeties" to a cannon between the main valve and the barrel.
Ball valves are also, being a torque opened valve, unable to be opened by the system pressure, or problems with that system pressure - which doubly makes them a wise choice for a safety.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Next

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'