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 58 users online :: 6 registered, 0 hidden and 52 guests


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

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

The Team
Administrators
Global Moderators
global_moderators.png CS

Mini Piston Hybrid

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
Sponsored 
  • Author
    Message

Mini Piston Hybrid

Unread postAuthor: PVC Arsenal 17 » Tue Jul 17, 2007 5:51 pm

First off, I thought of this while I was falling asleep. So there's a chance I'm missing some things and this whole idea could in fact be entirely stupid. If so, feel free to ignore it.

Basically, what I wanted to accomplish was a small, burst-disc-less hybrid. I kind of modified the concept of a coaxial piston gun. The idea is the same, except there is no manually operated pneumatic trigger, instead, there is only the piezo ignitor and a pop-off valve.

You fill the gun the same way you would any coaxial piston gun, but in this case you're filling it with premixed propane/air. You fill it to pressure slightly LOWER than the pop-off valve is set for. When the piezo is clicked, the propane/air mix ignites and pushes the piston back in the same fashion a typical pneumatic would when the pilot is vented. Only here, the pilot is compressed until the pressure inside overcomes the pop-off, allowing faster and easier movement of this piston backwards. O-rings on the piston will prevent the pilot from igniting as well. All the hot gasses then escape out the barrel. Hopefully...
  • 0

Attachments
piston hybrid.JPG

PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Unread postAuthor: spanerman » Tue Jul 17, 2007 5:55 pm

looks like it would work, the piston would need a cheack valve, and a nice big bumper. but it would work...
  • 0

Image

spanerman
Lieutenant Colonel
Lieutenant Colonel
 
Posts: 438
Joined: Sun Sep 17, 2006 2:54 pm
Reputation: 0

Unread postAuthor: noname » Tue Jul 17, 2007 6:04 pm

Great minds must think alike. I had this exact same idea, down to the pop off valve and O-ring'ed piston a while ago, but never built due ot lack of funds and that the massive pressure of a hybrid could explode the gun because of the self-modified bushing.
  • 0

User avatar
noname
Lieutenant General
Lieutenant General
 
Posts: 2699
Joined: Mon Apr 10, 2006 9:19 pm
Location: Bay Area, CA
Country: United States (us)
Reputation: 9

Unread postAuthor: homedepotpro » Tue Jul 17, 2007 6:06 pm

the only thing i see wrong is IF the pressure somehow reaches behind the piston, and the pressure equalizes, then you have a bomb. also the temperature might eat at the O-rings
btw: great diagram, very detailed
  • 0

Last edited by homedepotpro on Tue Jul 17, 2007 6:07 pm, edited 1 time in total.
User avatar
homedepotpro
Lieutenant Colonel
Lieutenant Colonel
 
Posts: 443
Joined: Sun Nov 26, 2006 1:00 am
Reputation: 0

Unread postAuthor: anatov » Tue Jul 17, 2007 6:07 pm

Hmmmm...I just had an idea. Take the propane injection system and put that further up, say in the front part of the gun, threaded into the coupling/bushing and pipe. Then replace the pilot valve with a schrader With that there, you pressurize the piston to be like your burst disk. The area behind the piston would be set at a much higher pressure than the hybrid's fuel is injected as. That way, when you press the ignition, the combustion would only push the piston out of the way when the pressure exceeded that of the air pressure behind the piston. This would allow for two things that are new to me as far as hybrids go, 1. You'd get a controllable pressure to release at, 2. You wouldn't need a burst disk.
  • 0


anatov
Private
Private
 
Posts: 22
Joined: Thu Nov 16, 2006 6:24 pm
Reputation: 0

Unread postAuthor: anatov » Tue Jul 17, 2007 6:08 pm

Actually, homedepotpro, if that happened then the pop-off valve would kick in.
  • 0


anatov
Private
Private
 
Posts: 22
Joined: Thu Nov 16, 2006 6:24 pm
Reputation: 0

Unread postAuthor: Flying_Salt » Tue Jul 17, 2007 6:58 pm

Yeah homedepotpro, it's only a very short pressure spike, and the pop of valve can be pulled off.

I've seen this concept floating around for a little pvc, it should work.
  • 0

sgort87 wrote:I hereby present Flying_Salt with The one and only <a href="http://www.geocities.com/sgort87/ghetto">Ghetto Award!</a>
User avatar
Flying_Salt
Brigadier General
Brigadier General
 
Posts: 779
Joined: Mon Oct 09, 2006 4:57 pm
Location: Texas
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: homedepotpro » Tue Jul 17, 2007 7:02 pm

i don't think the pop off valve would vent the air fast enough, if the air behind the piston ignited
  • 0

User avatar
homedepotpro
Lieutenant Colonel
Lieutenant Colonel
 
Posts: 443
Joined: Sun Nov 26, 2006 1:00 am
Reputation: 0

Unread postAuthor: Flying_Salt » Tue Jul 17, 2007 7:07 pm

Well then it would just pop off.
  • 0

sgort87 wrote:I hereby present Flying_Salt with The one and only <a href="http://www.geocities.com/sgort87/ghetto">Ghetto Award!</a>
User avatar
Flying_Salt
Brigadier General
Brigadier General
 
Posts: 779
Joined: Mon Oct 09, 2006 4:57 pm
Location: Texas
Reputation: 0

Unread postAuthor: Fnord » Tue Jul 17, 2007 9:14 pm

Let me just confirm this- Your design WILL work, as it's working for me right now.
The only difference is I fill the propane from the front, and then compressed air from the back (and I don't use a coax setup, because of the better flame front propagation an open chamber gives)

I don't even use a pop-off valve, and it still works just fine. Make sure you use metal for the chamber, I wouldn't trust pvc with this design.

The only problem I can see is rough metal could wear out the o-rings and allow the mixture behind to ignite. However, sch 40 steel can contain a 4x mix safely. I also know that because it happened to me before(projectile sealed itself inside the barrel).
Just smooth it out and grease er' up :)
  • 0

Image
User avatar
Fnord
Major General
Major General
 
Posts: 2244
Joined: Tue Feb 13, 2007 9:20 pm
Location: Pripyat
Reputation: 7

Unread postAuthor: PVC Arsenal 17 » Tue Jul 17, 2007 10:41 pm

Now I'm really considering making this... hmmm.

But I have an r/c helicopter to buy parts for, and a $200 plane to get. Eventually you'll see it for real.
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Unread postAuthor: PVC Arsenal 17 » Thu Jul 19, 2007 2:54 pm

Maybe I'll work on this sooner than I thought.

In that case, how much travel do you think a piston should have if the chamber is 6" of 1" brass pipe? The piston will most likey be inside it.
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Unread postAuthor: lukemc » Thu Jul 19, 2007 3:13 pm

What the heck? i had a very similer idea but with a burst disk in back instead of a blow off
  • 0

"Those who are different change the world. Those who are the same keep it that way"
User avatar
lukemc
Colonel
Colonel
 
Posts: 565
Joined: Sun Feb 25, 2007 8:48 am
Location: NY
Reputation: 0

Unread postAuthor: Pete Zaria » Thu Jul 19, 2007 4:03 pm

I think this concept would work, however, I would try hard not to pressurize the area behind the piston with an air/fuel mixture. I know the pop-off valve should take care of it if the pilot volume ignited, but I wouldn't trust a pop-off to vent the combusting, expanding pilot volume fast enough to prevent pipe failure.

A half-inch union with a burst disk behind the piston might be better.

I'd use two or more O-rings on the piston (to hopefully prevent any fuel from getting back there) and inject the fuel from the front of the chamber. Use anatov's idea of putting a schrader (or quickconnect) behind the piston so that you can pressurize the pilot area with air (it needs to be only slightly higher than the pre-combustion mix pressure...). You could also employ a light spring to keep the piston closed while fueling. Keep the pop-off behind the piston, too, just in case.

I would NOT build this out of any type of plastic pipe (I don't care if you find 800-psi rated sch160 nsf-pw PVC, I still wouldn't recommend it).

Just my input.

Peace,
Pete Zaria.
  • 0

User avatar
Pete Zaria
Moderator
Moderator
 
Posts: 978
Joined: Fri Mar 31, 2006 6:04 pm
Location: Near Seattle, WA
Reputation: 0

Unread postAuthor: PVC Arsenal 17 » Thu Jul 19, 2007 7:44 pm

I want to stick with the pop-off behind the piston since the idea was to make a small, disc-less hybrid.

I'm planning on building this out of brass, so I should be safe as far as that goes.

If I want to thread a schrader into brass pipe (for propane filling), should I solder on layers of copper for a better hold?
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Next

Return to Hybrid Cannon Discussion

Who is online

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

Reputation System ©'