Backwards Piston

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
User avatar
PeteS
Specialist
Specialist
Posts: 179
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Contact:

Fri Oct 04, 2013 4:56 pm

Is there any reason a piston in a coaxial should not be designed to be put in backwards from the way they usually are? By backwards I mean with the cupped end forward so the barrel extends into the piston.

The reason I am wondering is that I am trying to build a very short coaxial with the barrel being as long as possible for the short gun. By reversing the piston I figure that I can extend the barrel farther back in the launcher. It will also be easier to minimize the volume behind the piston.

The launcher will have an outer tube of 3" PVC, a piston turned down from a 2.5" end cap, and a 1-1/2" PVC barrel.
User avatar
Labtecpower
Sergeant 3
Sergeant 3
Eritrea
Posts: 1291
Joined: Sat Feb 20, 2010 6:38 am
Location: Pyongyang
Has thanked: 1 time
Been thanked: 3 times

Fri Oct 04, 2013 5:18 pm

I do not see any reason why it would have any disadvantages :)

For the sealing face you can maybe just use epoxy to attach a rubber sheet on the inside of the piston, no need for screws I think..
CannonCreations
Private 3
Private 3
Posts: 57
Joined: Fri Sep 02, 2011 9:30 am

Fri Oct 04, 2013 5:23 pm

yeah, you should be able to make a gun with a piston in that configuration, but you will actually need to increase the area behind the piston so that it can move back far enough. Also I dont know how much more barrel you could add with a piston like that, or if it would even make any difference. If you really want to cut down on the space behind the piston, cut it out completely, and instead you could try a diaphram. I have never personally used one as a valve for any of my cannons, but Im sure someone else here has
User avatar
dart guy
Specialist 3
Specialist 3
Posts: 394
Joined: Mon May 13, 2013 7:54 pm
Location: not telling you

Fri Oct 04, 2013 6:44 pm

gimme about 3 muinuts and i will post a piston idea
edit Image
the orings on the bigger part have 2 notches (not all the way around) and the black peice is a peice of rubber, the other orings are just for somethin to keep it on, hope you like my idea.
when life gives you lemons... make root beer and leave the world wondering how you did that :D
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 25745
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 73 times
Been thanked: 48 times

Donating Members

Fri Oct 04, 2013 7:24 pm

hectmarr wrote:You have to make many weapons, because this field is long and short life
User avatar
Technician1002
Captain
Captain
Posts: 5189
Joined: Sat Apr 04, 2009 11:10 am

Sat Oct 05, 2013 12:37 am

Way back, I saw a coax design that used a soup can in a 3 inch chamber with a rubber gasket bolted inside the can and covered with felt to adjust the fit. This can piston apparently worked well. I don't remember the barrel size. Think it was 1.5 inch or 2 inch.

I'm not going to try to find a thread that old. Not even sure it was on this site. Many have been on one of the early Spudgun Ring Exchange sites.
User avatar
jrrdw
Moderator
Moderator
United States of America
Posts: 6531
Joined: Wed Nov 16, 2005 5:11 pm
Location: Maryland
Has thanked: 10 times
Been thanked: 3 times
Contact:

Donating Members

Sat Oct 05, 2013 6:33 am

Wow I forgot about that L0L. Jeepkan had the better build in that thread (in hind sight).
Look if you must.
User avatar
PeteS
Specialist
Specialist
Posts: 179
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Contact:

Sat Oct 05, 2013 9:51 am

A schematic sketch of what I am thinking:
Attachments
short1_5,jpg.jpg
User avatar
Gun Freak
Lieutenant 5
Lieutenant 5
Posts: 4971
Joined: Mon Jan 25, 2010 4:38 pm
Location: Florida
Been thanked: 7 times

Sat Oct 05, 2013 11:06 pm

The good part about such a piston is that if you use a flexible material such as rubber, the piston acts as a check valve. With pressure inside of it, it will expand and not allow air flow into the pilot upon triggering. It can still let air by during filling.

Maybe you could try the idea out with one of those rubber clamp-on repair caps, or whatever they're called. Might need to reinforce the back with metal.
OG Anti-Hybrid
One man's trash is a true Spudder's treasure!
Golf Ball Cannon "Superna"M16 BBMGPengunHammer Valve Airsoft SniperHigh Pressure .22 Coax
Holy Shat!
User avatar
PeteS
Specialist
Specialist
Posts: 179
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Contact:

Sun Oct 06, 2013 8:27 am

Gun Freak wrote:The good part about such a piston is that if you use a flexible material such as rubber, the piston acts as a check valve. With pressure inside of it, it will expand and not allow air flow into the pilot upon triggering. It can still let air by during filling.

Maybe you could try the idea out with one of those rubber clamp-on repair caps, or whatever they're called. Might need to reinforce the back with metal.
Interesting...
I may give that a try.

The current configuration may already be doing that to some extent because the piston is made from a 2-1/2" cap and the wall of the side are turned down pretty thin.

BTW: I test fired the launcher this morning and it works pretty well. No real testing just a shot at 60 PSI or so. It went something like 120 yards. I don't think that is too bad for such a short launcher (about 18" total length).
Post Reply