SpudFiles

I just finsished my first full-sized coaxial cannon. It seals perfectly might i add.

Well i just test fired at 60 PSI. And when i fired it shot but it made a weird noise. If you've ever played paintball, it sounded kind of like the sound guns make whent hey run out of co2. You know, that bdddda sound. It wasnt as long as when a paintball gun does it. It was like 2 pops. The projectile shot but it sounded much different than any cannon ive heard and much different than i expected. Does anyone know why?

Im piloting with a 1/2 ball valve and my chamber is 2 inch and the barrel is 1 inch. I guess it has something to do with the piston.

Any ideas?

Is the power good?

How much total piston travel do you have?

How good of a fit is the piston?

Perhaps the ball valve is opening too slowly causing the valve to honk. Does it seem to be dependent on how fast (and forcefully) you open the ball valve?

A 1/2" ball valve should be sufficient for a 2" piston. As jimmy said, how fast are you opening the valve. Also, the fit of the piston could affect this as well...

I think it might be the sealing surface, if it's not enough tightened, it will
vibrate when air goes in the cannon causing honking.

i already had this problem with a coaxial....

The piston is tight but will move when pushed with a little bit of force.

I have more piston travel than i should but i was not sure how to reduce that. I was thinking maybe putting a pill bottle on the back my piston to reduce it is about 1/4 inch.

Im going to go test it for power and distance right now to see if the honking sound will really affect anything.

Well reply back if you dont mind and i will keep you updated.

What's the pilot volume like?

Uhh maybe a little under two inches.

I just realized i had a sprinkler valve laying in my yard. I threw that on the back instead of the 1/2 inch ball valve. When i try to pilot, it honks real loud out of the sprinkler valve and then the piston pilots and just a little air comes from the barrel.

I assume the reason for this is because of the flow restriction.

On the pilot side i have a 2 inch to a half inch bushing and then a 1/2 inch nipple screwed into it and then a 1/2 inch to one inch adapter and then the 1 inch sprinkler valve.


If i get a 2 inch to 1 inch bushing instead of the 2 inch to 1/2 inch businhg and screw the sprinkler straight in that should fix this problem shouldnt it? Im pretty sure but i just want to confirm it.

You need to be very specific if you're going to simply describe things.

Do you mean your piloting route is 2" long? Or do you mean your pilot volume is 2 cubic inches?

Spending more money before finding the problem isn't going to help you.

There is something out of whack with this, and it needs to be found first.

A complete, accurate, and current description seems to be in order here.

Is there any way you can post pictures?

I dont have my camera right now but i will try to explain better.

With the back of my cannon opened, where the piston goes, i push my piston into the pipe and i push it up against the barrel and then there is a little under two inches of pipe left behind the piston, which is where the piston would travel.

I hope that makes more sense. I know that is way too much but i accidently glued my barrel into the bushing a little short.

Stuff happens.

I think you have piston bounce. ie. The pilot volume is re-compressing, and causing the piston to reverse direction.

That's why it honks.

Take up the volume with something. The spacer should be something which will not compress under pressure. (Don't use foam.)

Leave 1/4" to 3/8" total piston travel.

Wood will likely be your best bet.

Also, I checked the other thread about your piston, and could not find out how you made your piston. If it's hollow at the back, it is likely contributing to the problem as well.

Thank you for your help.

How should the wood fit? Should it be as tight as the piston is? or just connected to the back of the piston to take up space without really acting as part of the piston.

And i believe the thread you are speaking of is about my mini coaxial. That piston was made entirely of epoxy.

This piston is made drom an end cap. And yes the back side is hollow. Should i feel it in to help fix the problem?

iisthemuffin wrote:Thank you for your help.

How should the wood fit? Should it be as tight as the piston is? or just connected to the back of the piston to take up space without really acting as part of the piston.


If you connect the wood to the piston, it becomes part of the piston, doesn't it? Don't connect it. It should fit reasonably close, if it fits as good as the piston, that's good enough.



And i believe the thread you are speaking of is about my mini coaxial. That piston was made entirely of epoxy.


No, you have a thread looking for a 2" piston.



This piston is made drom an end cap. And yes the back side is hollow. Should i feel it in to help fix the problem?

Yes, seal off the back side, or fill it in with something. (not foam) This extra volume is adding to your pilot volume, compounding the problem.




Do you have another end cap? If you were to put two end caps, on a piece of pipe (just the right length?), the finished product should take care of both problems. ( Jeeze, I think I read that somewhere! )

Don't forget some sort of bumper.(you can use foam for this) I suggest that bumpers be attached to the bushing that the piston impacts. This way, they do not increase the weight of the piston.


Edit: Note to self: Do not insert comments when quoting! :banghead: