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 44 users online :: 2 registered, 0 hidden and 42 guests


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

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

The Team
Administrators
Global Moderators
global_moderators.png CS

Interesting new valve design.

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

Interesting new valve design.

Unread postAuthor: Biopyro » Tue Mar 10, 2009 12:41 pm

http://inteltrailblazerschallenge.wikispaces.com/The+brag+zone

Basically, these guys had to design a t-shirt cannon, but they made a new valve. It's a coaxial sort of design from what I can tell, but the initial actuation is manual.

Because of this is has no pilot volume and you can fill from the chamber port.

I may have misinterpreted the operation, but this seems to be it.

I was involved with an engineering challenge building a t shirt launcher in a competition. To win the competition, we spent a good part of our time building a better valve. The valve is designed to beat ball valves in speed, sprinkler valves in flow, and piston valves in operating pressure range.

The official wiki for the project is here;
http://inteltrailblazerschallenge.wikispaces.com/

How it works can best be seen in this you tube video;

http://www.youtube.com/watch?v=9Klxqav_6NM
  • 0

Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
User avatar
Biopyro
Colonel
Colonel
 
Posts: 656
Joined: Fri Aug 04, 2006 5:32 am
Location: UK
Reputation: 0

Unread postAuthor: ALIHISGREAT » Tue Mar 10, 2009 1:02 pm

JSR made a coax called the beast i do believe that had a mechanical pilot mech... but i can't find a link atm.
  • 0

<a href="http://www.bungie.net/stats/halo3/default.aspx?player=ALI H IS GREAT"><img src="http://www.bungie.net/card/halo3/ALI H IS GREAT.ashx"></a>
Image
User avatar
ALIHISGREAT
Major General
Major General
 
Posts: 1779
Joined: Sat Aug 25, 2007 6:47 pm
Location: UK
Reputation: 0

Unread postAuthor: Hotwired » Tue Mar 10, 2009 2:20 pm

Not the same thing.

JSR's cannon held back the piston with a sear.

This one uses a balanced o-ringed piston to seal the ports then unbalances it by cracking open the valve by hand.

Good fix on separating the piston from the manual trigger when the air pressure engages it.

Also, it doesn't have to be a coaxial, in the same way a conventional coaxial and a barrel sealer are essentially the same but arranged in different ways.


Also...

Code: Select all
5.a: NO GAS POWERED ITEMS will be allowed in the Rose Garden Arena ("Arena");


Instant fail or is this an American way of saying no petrol powered cannons or perhaps even combustion cannons?
  • 0

User avatar
Hotwired
Lieutenant General
Lieutenant General
 
Posts: 2599
Joined: Fri Oct 13, 2006 5:51 am
Location: UK
Reputation: 0

Unread postAuthor: MRR » Tue Mar 10, 2009 2:46 pm

I think it's the way Hotwired said.
A balanced piston that is easy to move because there is no specific pressure on one side.

I was thinking to build a trigger like that.

Image
  • 0


MRR
Major
Major
 
Posts: 362
Joined: Tue Feb 17, 2009 2:29 pm
Reputation: 0

Unread postAuthor: Biopyro » Tue Mar 10, 2009 2:52 pm

I don't think I'm understanding it correctly then?
I'm pretty sure the barrel has to extend all the way through to the "pilot" port, and I really don't get the snooker cue analogy :(

I thought that when the guide rod is pulled, the piston's face is exposed, pushing it all the way back through the barrel, and allowing air to escape in front of it out of the barrel.

Image

Edit: Wow your diagram looks better haha! Yeah so it does really have to be coaxial to some extent because the barrel must go all the way throught the air chamber.
  • 0

Last edited by Biopyro on Tue Mar 10, 2009 2:54 pm, edited 1 time in total.
Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
User avatar
Biopyro
Colonel
Colonel
 
Posts: 656
Joined: Fri Aug 04, 2006 5:32 am
Location: UK
Reputation: 0

Unread postAuthor: clide » Tue Mar 10, 2009 2:54 pm

I've seen the design idea come up a few times. The closest thing I remember being built was a cannon by the name of Big Red. It used the same basic configuration of a balanced piston inside a tube in the chamber, but they were using a positive pressure pneumatic triggering system to pull the piston back. http://tinyurl.com/cbblha

I was going to build a version of this idea in a tee configuration a while back to test it's actuation speed, but I screwed up while gluing the tee in place and never got around to rebuilding it.
  • 0

<a href="http://gbcannon.com" target="_blank"><img src="http://gbcannon.com/pics/misc/pixel.png" border="0"></a>latest update - debut of the cardapult

clide
Donating Member
Donating Member
 
Posts: 785
Joined: Sun Mar 06, 2005 3:06 am
Location: Oklahoma, USA
Reputation: 0

Unread postAuthor: Hotwired » Tue Mar 10, 2009 2:58 pm

Analogies get in the way of the facts.

The trigger rod is NOT connected to the piston.

It slides through the piston. A small pin on the trigger side pushes the piston forward to seal then the rod is pulled backwards through the piston so that the nut on it's tip hits the piston and pulls it back enough to open the port.

The air pressure then engages the barrel side of the piston and blows it down the trigger rod til it hits the buffers, fully exposing the porting.

It doesn't cause the trigger rod to get thrown back with force because it isn't physically connected.
  • 0

User avatar
Hotwired
Lieutenant General
Lieutenant General
 
Posts: 2599
Joined: Fri Oct 13, 2006 5:51 am
Location: UK
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: jackssmirkingrevenge » Tue Mar 10, 2009 3:00 pm

clide wrote:I've seen the design idea come up a few times.


My first ever pneumatic used this design, cobbled together from a PET bottle, a couple of syringes and yes, my first use of epoxy :)
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Biopyro » Tue Mar 10, 2009 3:12 pm

Aha now I get it, thanks hotwired.

Seems like it would be a very good design becuase there isn't a pilot to empty.
Also it would be easy to have a very light piston, and very good flow would it not?
  • 0

Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
User avatar
Biopyro
Colonel
Colonel
 
Posts: 656
Joined: Fri Aug 04, 2006 5:32 am
Location: UK
Reputation: 0

Unread postAuthor: Hotwired » Tue Mar 10, 2009 11:19 pm

Mmm, saves on the waste of pilot gas, also simplifies filling as you only fill the main chamber and not a pilot chamber.

Mass of the piston maybe, this one has to be a full bore solid slug aside from the trigger rod hole. With a similar level of machining you can use a lighter piston for a barrel sealer.

Overall a fairly solid valve style.

The only partial triggering means that the gas assistance only really kicks in bigtime if the projectile has enough mass to it, giving the resistance to force back the piston the other way. If the projectile gives too little resistance it could be out before the valve had finished opening itself.
  • 0

User avatar
Hotwired
Lieutenant General
Lieutenant General
 
Posts: 2599
Joined: Fri Oct 13, 2006 5:51 am
Location: UK
Reputation: 0

Unread postAuthor: inonickname » Wed Mar 11, 2009 2:35 am

Wow, I like their method of piston construction.

Nice, interesting valve..but I'll have to try that method.
  • 0

PimpAssasinG wrote:no im strong but you are a fat gay mother sucker that gets raped by black man for fun
User avatar
inonickname
Lieutenant General
Lieutenant General
 
Posts: 2606
Joined: Sun Dec 07, 2008 3:27 am
Reputation: 0

Unread postAuthor: ALIHISGREAT » Wed Mar 11, 2009 2:43 am

  • 0

<a href="http://www.bungie.net/stats/halo3/default.aspx?player=ALI H IS GREAT"><img src="http://www.bungie.net/card/halo3/ALI H IS GREAT.ashx"></a>
Image
User avatar
ALIHISGREAT
Major General
Major General
 
Posts: 1779
Joined: Sat Aug 25, 2007 6:47 pm
Location: UK
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Wed Mar 11, 2009 2:56 am

ALIHISGREAT wrote:ahh so its more like this


Not really, unless you push the "piston" forward and fire it as a projectile. The design in that patent will give you 100% flow as soon as the rear end of the projectile passes the breech end of the barrel, effectively it would be slightly better than a burst disk.

The design that's the subject of this thread on the other hand has all the limitations of a piston valve. Granted there's no pilot pressure and the piston is smaller and therefore lighter, however it does have a smaller surface area and doubtless more friction since it needs to be an airtight seal.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: Biopyro » Wed Mar 11, 2009 4:41 am

Surely the valve can be more efficient than a normal coaxial, because the piston is the size of the barrel, not the chamber, which cancels out the surface area loss by weighing less?

Overall I'd be inclined to say this would perform better, and if not then certainly you don't have the wasted pilot air.
  • 0

Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
User avatar
Biopyro
Colonel
Colonel
 
Posts: 656
Joined: Fri Aug 04, 2006 5:32 am
Location: UK
Reputation: 0

Unread postAuthor: Technician1002 » Sun Apr 05, 2009 1:19 am

Biopyro wrote:I don't think I'm understanding it correctly then?
I'm pretty sure the barrel has to extend all the way through to the "pilot" port, and I really don't get the snooker cue analogy :(

I thought that when the guide rod is pulled, the piston's face is exposed, pushing it all the way back through the barrel, and allowing air to escape in front of it out of the barrel.

Image

Edit: Wow your diagram looks better haha! Yeah so it does really have to be coaxial to some extent because the barrel must go all the way throught the air chamber.


The diagram is close. One important thing missed. The ports are right smack up against the very front of the tank. The piston does not go all the way through the tank when this is fired. It is limited to about 1.5 inch travel in the 2 inch cannon and 3/4 inch in the 1 inch cannon. It doesn't move very far. Since the rod and knob weigh more than the piston, getting this up to speed before contacting the valve, helps the initial opening.

The snooker cue analogy is simply mentioning since the piston is not attached to the rod, the rod can have a couple inch stroke before contacting the piston, knocking it open instead of just pulling it along.

It does not have to be coaxal at all. This can be built inside a T which is then screwed onto a tank like a supah valve.

I have started a thread on this valve design. I hope to answer all your questions. Look for a thread on a Quick Dump Valve. I found out that is what this design is. It is most often used to quickly dump large liquid holding tanks and is air operated instead of manual.

The only partial triggering means that the gas assistance only really kicks in bigtime if the projectile has enough mass to it, giving the resistance to force back the piston the other way. If the projectile gives too little resistance it could be out before the valve had finished opening itself.


I have found the mass of the air in the barrel is plenty. Check out my youtube videos with the same user name. Look for the one with the blue plastic bucket. The back pressure is enough to do the job. With some tricks with the o rings to reduce friction, it works very well.

Appreciated, but just a small note on forum etiquette, try and avoid making consecutive replies to a thread when you could easily condense them into one


Tried to fix it, but can't seem to delete the prior post.

Surely the valve can be more efficient than a normal coaxial, because the piston is the size of the barrel, not the chamber, which cancels out the surface area loss by weighing less?

Overall I'd be inclined to say this would perform better, and if not then certainly you don't have the wasted pilot air.


Most important is the lack of pressure behind the piston, so when the chamber pressure opens it, it can open faster instead of pushing against a pressurized area.

The surface area is not important if there were the same pressure in the pilot area. A three inch piston 2 inches thick pushed by 100PSI will fly the same speed as a 1/2 inch piston 2 inches thick. The 1/2 inch piston does not need to be as thick as the 3 inch. :lol:

In summary, no back pressure, possibly thinner = faster. I used a low mass material. It floats. It is less than 1/2 the weight of aluminum.

The design that's the subject of this thread on the other hand has all the limitations of a piston valve. Granted there's no pilot pressure and the piston is smaller and therefore lighter, however it does have a smaller surface area and doubtless more friction since it needs to be an airtight seal.


This valve was designed to eliminate some of the limitations of a piston valve. The three items this fixes is;

Operating pressure range
Difficult to get to seal
Friction with high blowby causing sticking in either open or closed positions.

Friction is a biggie and was addressed in the design. I'll be covering the friction issue on the thread i started on the Quick Dump Valve. I built the marshmallow cannon as a second generation of the t shirt launcher to test some o ring use. The new cannon uses a 1 inch valve. The friction is so low, that when not under pressure, simply pointing it up and giving a light shake will open the valve by gravity. I'll cover how this works on the other thread.

This valve seals easily and fills with a bicycle pump. No high volume compressor needed to get the piston to seal.

It has low leakage. No high volume compressor needed to keep ahead of leaks.

It triggers easily at all pressures all the way down to zero. I have barrel acceleration graphs where the expansion volume was less than the volume of the barrel causing vacuum on projectile exit.

http://www.spudfiles.com/forums/quick-dump-valve-t17858.html

I am working on a video to show the valve construction and details on low friction use of o rings. I hope to have something up online in the next week or two.

Biopyro wrote:Surely the valve can be more efficient than a normal coaxial, because the piston is the size of the barrel, not the chamber, which cancels out the surface area loss by weighing less?

Overall I'd be inclined to say this would perform better, and if not then certainly you don't have the wasted pilot air.


One of the big reasons to play with this design was building for speed. Turbulence in the valve area limits the flow when near supersonic. In a traditional coaxial, the valve is near or at the very rear of the chamber. The air flow has to make a high speed U-turn in an area full of square corners and edges.

On the down side, this design has 2 area needing a good seal, unlike a piston which needs only one, so designing to eliminate friction is important to keep it fast. In theory a regular piston would have less moving friction. Individual results may vary considerably.

When not under pressure, this valve can open by gravity and a mild shake. More on the low friction design later.

Moving the valve to the other end of the tank eliminates a 180 degree turn and takes the high velocity flow and does a lane change as the air moves from the rear of the tank and takes a wiggle into the barrel. Not perfect, but in theory it might be better.

The other design consideration is the chamber shape. The less the air has to pick up speed before reaching the valve, the less Turbulence it will have when reaching the valve. This in theory should help get air from the tank into the valve.

I think a combination of these helped the apple in the 2 inch valve version reach 882 FPS. I'm not sure traditional piston valves reach this speed at below 100 PSI. Anyone have good chronograph readings of coaxial spud and apple launches for comparison?

Good fix on separating the piston from the manual trigger when the air pressure engages it.


Thanks. This was inspired by our desire to have a hand left. The math on the 2 inch valve came out to an opening force of 314 Lbs if it was coupled in a 100 PSI shot. We could see the rod stuck through someone's hand. When it was decided to decouple, we realised the lowered moving mass would help the piston speed.
:wink:

**Edit**
For safety, I used the big round ball in the big cannon and a big trigger knob on the marshmallow cannon. If the stop assy failed, it would protect against a nasty spear through the hand.

The second safety item in the design is the use of a 1/16th inch diameter wire pin to close the valve. If the stop failed, the pin is designed to shear off. This happed in the little cannon when the pin was too far forward and the piston hit it.

In the In using the quick couplers with no check valve prevents accidents from leaving it loaded. Unhook the hose and on the large launcher leave the ball valve open and the cannon is safe.

In both launchers, the original tank safety device was left fully functional. The Freon tank has the original rupture disk and the little one has the relief valve.

Think Safety
  • 0

Last edited by Technician1002 on Wed Apr 08, 2009 5:49 am, edited 14 times in total.
User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Next

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Google [Bot], Yahoo [Bot]

cron
Reputation System ©'