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 62 users online :: 4 registered, 1 hidden and 57 guests


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

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

The Team
Administrators
Global Moderators
global_moderators.png CS

Barrel-Sealing Piston Gun 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

Barrel-Sealing Piston Gun Problems

Unread postAuthor: spudkilla224 » Wed Jul 30, 2008 11:33 am

I have done some research on barrel-sealing piston cannons, on how tight the piston should be, and how far back it should move, but i am confused on how to make my piston more stable in the back.

My piston is housed in a 2" Tee, and my piston itself it made from a 1.25" coupler with some tape wrapped around it ,the sealing face of the piston is a mouse pad. does this design sound like it would work? it just seems that the piston isn't big enough in diameter of the 2" Tee. And one other thing i have a question about is when i push the piston to see how the seal is against the barrel it looks fine, but it looks like there is some space behind the tape and the tee. the tape only is wrapped to the center of the 1.25" coupler and it ends at the tip of the barrel seal.

any help would be appreciated.
  • 0

Attachments
0730081342a.jpg
Piston in Tee
0730081342b.jpg
Piston Housing
0730081343a.jpg
My questionable piston.
Last edited by spudkilla224 on Wed Jul 30, 2008 1:53 pm, edited 1 time in total.

spudkilla224
Corporal
Corporal
 
Posts: 65
Joined: Wed Mar 19, 2008 8:04 pm
Reputation: 0

Unread postAuthor: mobile chernobyl » Wed Jul 30, 2008 11:54 am

the 1.25" fittings will allow too much wobble. do this:


about 5-6" of 3/8 thread all-thread rod.
Three 2" fender washers (Has 2" OD, ID slightly oversize - read on - available at lowes/depot)
Two large 3/8" washers (about 1.25" OD available at lowes/depot)
Two 2" OD by 3/8" ID Rubber washers from Home depot
Six 3/8 thread nyloc nuts.

This will be built like a shishkabob, the 5-6" allthread rod being the skewer, I'll explain it from sealing side to exhaust side:

Nyloc, large 3/8 washer, 2" rubber washer, 2" fender washer, nyloc nut
about 1.5"-2"
Nyloc, large 3/8 washer, 2" rubber washer, 2" fender washer, nyloc nut
about 1.5"
Nyloc, 2" fender washer, Nyloc

The only tricky part is with the 2" fender washers you will NEED to have the nylon end of the nyloc bolt facing the 2" fender washer. The nylon smaller part fits snug in the 2" fender washer centering it since it is slightly larger than the standard hole in a 3/8" washer.

There you go, an awsome, cheap, and super easy to make piston that seals pretty well both barrel and exhuast side. 2" fender washers fit with .049" (a little less than a sixteenth) clearance give or take .005" in 2" PVC (What you'll use on the one side of the Tee where the valve goes). There is very minimal wobble, and any that exists is permitable as it will straighten up when pressure is applied (I could get it to seat with just my lungs).
  • 0

User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

Unread postAuthor: psycix » Wed Jul 30, 2008 12:40 pm

The piston outer diameter should approach the inner diameter of the pipe it slides in as much as possible. If its too loose, you can do 4 things:
-Find a bigger piston base
-Build a whole new piston out of other stuff (like the washer method or casted out of epoxy or hot glue)
-Wrap more duct tape (gives bad results, tape has to be perfectly smooth, one bump in it will screw it up. Tape might break down quickly)
-Use a sliding tube inside the tee, allowing smaller diameter pistons.
  • 0

Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

Spudfiles steam group, join!
User avatar
psycix
Donating Member
Donating Member
 
Posts: 3684
Joined: Mon Jun 25, 2007 7:12 am
Location: The Netherlands
Reputation: 0

Unread postAuthor: Pilgrimman » Wed Jul 30, 2008 12:53 pm

I have one question: (Maybe a dumb one) You know that the couplers only fit well in 2" PIPE not tees, right? If so, I see no problem with the design as you've described it.
  • 0

Yeah, we wouldn't want to anger the bees, now would we??

I HATE YOU BEES! I HATE YOU BEES! I HATE YOU BEES!

LMAO Classic!!!! I love Family Guy!
User avatar
Pilgrimman
Lieutenant Colonel
Lieutenant Colonel
 
Posts: 481
Joined: Thu Jun 28, 2007 1:10 pm
Location: Grants Pass, OR
Reputation: 0

Unread postAuthor: MrCrowley » Wed Jul 30, 2008 2:26 pm

It wont work:

1) The tape is only at the front, this means the air can just go out near the back of the piston and if it does work it will jam because of the huge difference in diameter

2) The tape may cause it to jam even if you covered the whole piston as it doesn't look very smooth.

3) You said yourself even with the tape it's not a good fit.

Try a deodorant can or maybe plywood:
http://www.instructables.com/id/Golfbal ... That-Shoo/
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: spudkilla224 » Wed Jul 30, 2008 2:57 pm

Thanks MrCrowley, i hav a question for you about your wood piston, how long is it in length? or how long should my piston for a 2" Tee?
  • 0


spudkilla224
Corporal
Corporal
 
Posts: 65
Joined: Wed Mar 19, 2008 8:04 pm
Reputation: 0

Unread postAuthor: MrCrowley » Wed Jul 30, 2008 10:50 pm

It must be around 3.5" long. The length doesn't matter so much. Just make it long enough so it can seal against the barrel but still be supported at the back, and try and take up as much pilot volume with the length.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Sponsored

Sponsor
 


Unread postAuthor: frankrede » Thu Jul 31, 2008 12:09 am

I'm tired of damn barrel sealers being a pain in the ass.
I can't have a piston last for anything hah
I'M BUYING A MAULER
  • 0

Current project: Afghanistan deployment
User avatar
frankrede
Lieutenant General
Lieutenant General
 
Posts: 3220
Joined: Thu Jul 20, 2006 9:47 pm
Reputation: 0

Return to Pneumatic Cannon Discussion

Who is online

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

Reputation System ©'