PSV valve cannon.

[Alex345]

I recently started a topic about a large PSV valve i got for cheap, i was looking for a barrel and a chamber and the topic got quiet.

Now i have my barrel and chamber and have put together my cannon! Which is currently the largest one i've ever built, it has a 2 meter long 6/4 (48mm) barrel and a 24l overkill compressor tank.









Right now it's in it's "crude but functional" form.
Things that still need to happen:

Paint job (Maybe)
Carriage (Most likely)
More elegant triggering system (Definitely)
One 3/8 to 1/4 adapter for the pressure gauge instead of the current ghetto rigged setup (Definitely)
Leak proofing (Definitely)

Took several test shots, a few with just air from 3 to 5 bar and even then the cannon rolled back on its wheels!

And two shots with ammo, one potato and one solid wax candle which fitted inside the barrel nicely. Both shots were at about 8 bar

The potato exploded as soon as it left the barrel and the candle disappeared into the sky... I'm going to build some tracer rounds for it to see how far she goes

Funny thing i noticed though; When the pressure in the main chamber is at about 8 bars i need to put around 12 bar or more on the pilot in order to prevent it from leaking air from the barrel, so connecting the chamber to the pilot was not an option. Luckily i do have an an HPA rig for this.

[auxiliary]

I like it! It's cool to see the use of an unorthodox valve and I guess it works too!

I'd be careful about mentioning tracer rounds because discussion of incendiary projectiles is prohibited. You can attach a glowstick to some ammo and that might work. Good luck with fixing all the little problems. That always seems to be the hardest part.

[jackssmirkingrevenge]

Holy priceless collection of Etruscan snoods!

Nice to see the valve has found a good home.

Here's a suggestion... since you can pressurise the pilot independently, have you thought of making it an auto pop-off valve? It would seem that pressurising the pilot to the same pressure as the chamber would give you an effective system.

A powerful automatic golfball cannon would be a possibility...

I only did it with marbles: http://www.spudfiles.com/forums/marble- ... 20027.html

[Brian the brain]

I'd be careful about mentioning tracer rounds because discussion of incendiary projectiles is prohibited. You can attach a glowstick to some ammo and that might work

as a mod I'm assuming we are just talking glow in the darksticks,..?

Have you tried putting a spring behind the piston?
Between the main seal and that extra wall they've added?

Then you could hook up the pilot to the chamber so you wouldn't need to fill seperately...

If the side hole is plugged correctly you could simply remove the O-rings around the piston center-rod.

[Alex345]

@auxiliary: Thanks! Believe me, it works pretty well too The "tracer" round in question was a hollowed out candle with a vial filled with glow in the dark liquid from a glow stick in the middle

@jackssmirkingrevenge: I'm first going to work out all the kinks until i have a nice piece of backyard artillery. After that i'm planning on getting a smaller barrel and chamber to make a handheld of shoulder fired version

And when that's done i might think about going on such an automatic adventure Could you elaborate on how your marble cannon works?

@Brian the brain: Too little space for a string i'm afraid, and wouldn't that cause a slower opening time?


Anyway, took the "tracer" shot a moment ago, i guess it went about close to 200m. A little disappointing BUT the projectile only weighed about 58 grams. I'm working on a nice little custom projectile for you guys, the projectile itself weighs 227 grams and it still needs a cup/sabot so no total weight yet...

This thing DEFINITIVELY needs a carriage because the recoil is huge even with a 58 gram projectile... It's loud to, even with a 2m long barrel it makes my ears ring. And let me tell you, holding my ear next to the valve when the cannon is fully charged to check for leaks is terrifying!

I will upload pics from the tracer round soon

[jackssmirkingrevenge]

And when that's done i might think about going on such an automatic adventure Could you elaborate on how your marble cannon works?

Basically by feeding a limited flow to a pop-off valve, you can get it to reciprocate. Something like this: http://www.spudfiles.com/forums/custom- ... 17142.html

[youtube][/youtube]

If I understood your valve correctly, feeding it from the opposite side will cause it to act like a pop-off.

[Alex345]

If i feed from the other side (which i have done a few times by accident) the air pushes the piston down so that when i release the pilot the cannon simply won't fire.

The only way it would fire then would be to put a higher pressure on the unused hole on the side which would push the piston up.

[Brian the brain]

Okay..I checked you valve-topic again and I see what's going wrong.
First off...you need to flip the valve as your inport needs to be the outport.
The way you have it now the air is trying to push the piston back while it should be pushed against the seat.

You've made it a chamber sealer...
That would explain why you need higher pilot pressure..
It should be a barrel sealer..



Then you can modify it by drilling two small holes so that you can fill in one go.

[Alex345]

I see! I'll take the valve apart and see what i can do, any idea on the size of the holes i have to drill? Because i don't want to ruin it :p

In the mean time some pics of the tracer from the other day:

[Brian the brain]

There is one very important thing to check before you change anything.

The piston seat should be smaller than the back end of the piston for it to work like I said.

The bigger diameter back end generates more force than the smaller diameter front when it is piloted.I'm betting the differences are quite small in your valve.The amount of difference is not that important as long as the sealing end is smaller than the back.

If the diameters are equal or if the seal diameter is bigger it won't work.
I'd like to know the dimensions before you start drilling.



Once everything is checked and you are ready to go I suggest drilling the smallest hole you can.I'm a metric guy so I'd say 1mm.
All you need is for the air to pass through.

[Alex345]

Which part is the seat? Picture is upside down for some reason.

[dewey-1]

Measure with caliper if possible.

[Alex345]

Seat: 47mm
Piston: 54mm

Is a 3mm hole good? Because i have bad experiences with 1 and 2mm drill bits breaking during drilling...

[MrCrowley]

I think you should keep it how it is and just use more pressure in the pilot. It's not surprising that you need 12bar in the pilot when 8bar is in the chamber as the back of the piston looks smaller than the seat diameter.

[Brian the brain]

You should measure the BACK end of the piston.
That's the business end in this case.

Judging from what I see in the first picture I'm guessing mr.C is right..
In that case keep it like it is.