Rastamuffin Has Performance Problems

[rastamuffin]

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

[Insomniac]

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.

[starman]

How big is your ball valve?

[jook13]

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.

[SpudsMcGee]

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.

[john bunsenburner]

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.

[rastamuffin]

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

[Ragnarok]

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.

[jrrdw]

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.

Welcome to Spudfiles.

[rastamuffin]

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

[starman]

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.

[Ragnarok]

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.

[rastamuffin]

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

[jrrdw]

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.

[Ragnarok]

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.