SpudFiles

Finally made time to get the video together and add some silliness as well (have the sound on if you can)
Thanks again to the SF community and a special shout to JSR for all the great info. This is my first non-ball valve pneumatic. It's a barrel-sealing piston and let me just say that, after 10 million tries to get that damn piston to work, it was the most satisfying sound to finally hear it slam back.

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Like . Perfect for country walks

Extremely well done, love the can shot!

First off I would like to say I love your snipe stick. I am trying to build something similar to fit into a walking stick but I am getting lost somewhere.

your snipe stick is just like what I have been trying to make without success, I assume I'm having the same problem like your ten million attempts to get the valve slam back. I have that exact problem with my effort which looks very much like your idea but does not work:-) . The valve seals which is most peoples problem getting a seal, mine seals great no leaks but when I release the pump I get air leaking in a puff from the pump pipe where it connects to the shredder valve. I have tried different piston lengths but it is always the same end . I have tested that all the parts work individually i.e the barrel is not blocked , I have no leak from the barrel seal in the compression end cap. When I take off the pump pipe all the air comes out the shredder valve and not the barrel which is sealed by the piston.

Any ideas?

Smalldog wrote:When I take off the pump pipe all the air comes out the shredder valve and not the barrel which is sealed by the piston.

What king of pump are you using?

This kind of pump is ideal because you can independently close the schrader before disconnecting the pump, preventing it from firing prematurely.

Hi I have a pump like this now but no joy. It is strange as I had it working fine, it was really powerful and worked every time until it stopped . So I have some questions if it is ok to ask here .
I'm new to forum posting sorry if I am doing something wrong but i am lost.
My thing is very much like the snipe stick made from 15mm copper with a compression fitting one end , the barrel is fitted here with epoxy.

I have a shrader in the other end epoxied in

I have about 35 - 40 mm from barrel end to shrader

My piston is made from a white nylon type rod that is an easy fit in the copper tube say mm play all round , to this I have glued a rubber washer with a hole as my sealing face this is a better fit in the barrel but not a sealing fit.

When I pump this up the barrel and piston seal fine but pressing the valve does not suck the piston back what ever I try now and I have tried a lot . I have have made around 7 pistons of differing lengths and weight leaving a gap of 1 to 2mm up to 10mm from the valve and nothing works.
My question re pistons are should the piston seal in the barrel i.e a tight fit, I thought it had to be a leaking fit so air can get in front of the piston . I think I am just pressurizing the space behind the piston may be ? I don not know at this point i am close to giving up.

What gap is needed between piston an barrel end.

my thing seals ok and pressure goes up fine but it will not suck back the piston to let out the projectile. any idea where I am going wrong?

I liked the Snipe stick design it is what I am trying to fit into a walking stick eventually.

Thanks in advance

Gary and sorry if am posting in the wrong place>

My piston is made from a white nylon type rod that is an easy fit in the copper tube say mm play all round

There's your problem.

It should be a really tight fit, otherwise it will never pilot. When making epoxy pistons I would always cast the in the tube they would be riding in, because they would be as tight as possible without actually being airtight.

Hi,

|Thanks for the reply but if the piston is that tight i.e cat in the tube how will the air get into the main chamber past the piston assuming I have the correct idea. end cap with valve, piston sealing on barrel with small travel area in my case say 1/4 inch as I am using 1/2 inch pipe. how will the air get past the piston to the main chamber ? if cast in chamber it will be a good tight fit. This is boggling my mind being new to all of this.

I must be a lot of stupid I cant get it to work I just seem to get the piston stuck against the barrel making a seal and a puff of air from behind the piston and nothing else when I push the pin on the valve.

Thanks again Gary

Even with a really tight fit, without an o-ring air will still get through.

What is probably happening in your case is that when you open the pilot valve, air is rushing back from the main chamber to replace the air being lost through the pilot valve, meaning the pressure in the pilot chamber never drops enough for the piston to move.

Try wrapping some masking tape around your piston until it's tight enough to be really snug (but still able to move), you should see a difference.

Hi,

When I read It should be a really tight fit, otherwise it will never pilot from a post above I tried again making a new tighter piston and guess what it worked. All the time I pent trying to get the dam thing working and it was my misunderstanding that was stopping it. I read that air needed to flow around the piston into the chamber and so I thought it needed a gap to work.

Anyway thanks guys for your help I have my prototype working now and can get ideas on how to make a walking stick cannon (just for the fun of it) once it is done I will try something else then .

Very best regards for your help.

Gary

Well folks it finally works and just to show that it is some what like the Snipe Stick I'll add a picture. The blue tape is holding on a magnet I thought I would use it to keep the firing cap safe but it is brass , oops! This thing is so powerful at 150 PSI it wrecks old dvd's and went through a milk bottle and two thick cardboard boxes wow it packs a wallop, it's a bit scary really how powerful it is . I used a blue thread sealer on the joints that works great a 50 ml tube is about £2.50 from tool station, it is way better than PTFE tape and drys quite fast.

Thanks for all the help now it's off to build a bigger onehttp://www.spudfiles.com/posting.php?mode=reply&f=1&t=26349#

Regards

Gary

Awesome! It reminds me of the guns I have been designing. I can't make any yet but I have a sketchbook filled with pneumatic rifle and pocket shooter plans. Mostly made out of copper tubing.

Hey! I like to take a year+ to get back to people...

Sorry, but I've been away and I must have turned off notifications or something. Anyway, I'm glad to see master sensei, JSR, helped you out. Your finished design looks great.