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 45 users online :: 4 registered, 0 hidden and 41 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

What is the limiting factor

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

What is the limiting factor

Unread postAuthor: Guaps » Mon Oct 18, 2010 12:44 pm

I am building a cannon with an interchangeable barrel so I can shoot anything from marbles (~1/2" barrel) to full potatoes (~2" barrel).

If I use the ebay QEVs mentioned in this thread, will that work for a 2" barrel? Is a 1/2" valve too small?

Thanks!
  • 0


Guaps
Private
Private
 
Posts: 10
Joined: Fri Oct 15, 2010 6:50 pm
Reputation: 0

Unread postAuthor: Technician1002 » Mon Oct 18, 2010 12:50 pm

It depends on what is acceptable performance. Are you trying to launch spuds cross the yard or trying 3 football field lengths, or something in between?

Personally don't use barrels more than twice the diameter of the valve's orifice. If possible I use barrels no more than 1.5 times the diameter.

If your 1/2 inch valve has a 3/8ths inch orifice, a 3/4 inch barrel is about the largest you will get reasonable performance from.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: Guaps » Mon Oct 18, 2010 1:07 pm

I'm hoping to put a potato into low earth orbit, but i'll settle for a few football field lengths. :D

Thanks for the 2x orifice rule of thumb. That's exactly what I was looking for.

Is there a similar rule of thumb for canister size and barrel size/length?
  • 0


Guaps
Private
Private
 
Posts: 10
Joined: Fri Oct 15, 2010 6:50 pm
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Mon Oct 18, 2010 3:45 pm

Technician1002 wrote:If your 1/2 inch valve has a 3/8ths inch orifice, a 3/4 inch barrel is about the largest you will get reasonable performance from.


Not sure about QEVs but the ball valves I have have a significantly larger orifice than their stated diameter.
  • 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: Ragnarok » Mon Oct 18, 2010 6:30 pm

To expand on what Jack said, the nominally half inch "European"/Piston style QEV I've got has a 14.2mm (0.56") seat diameter.

Not that that will necessarily apply here, but they can easily be bigger than their nominal size.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: lozz08 » Mon Oct 18, 2010 7:17 pm

If I were you, I'd go with the larges QEV I could find. An interchangeable barrel of a smaller size can screw in via adapters and you wont lose any performance. Why not try making a larger piston valve yourself from a tee and such? Plenty of info on that here.
  • 0

User avatar
lozz08
2nd Lieutenant
2nd Lieutenant
 
Posts: 239
Joined: Wed Jul 01, 2009 7:33 am
Reputation: 0

Unread postAuthor: Technician1002 » Mon Oct 18, 2010 8:10 pm

If going for competition performance and low earth orbit, the rule of thumb is use a valve with larger flow than your barrel so the restriction to flow is due to the barrel size, not the valve.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Sponsored

Sponsor
 


Unread postAuthor: Selador » Fri Nov 12, 2010 2:34 am

Technician1002 wrote:If going for competition performance and low earth orbit, the rule of thumb is use a valve with larger flow than your barrel so the restriction to flow is due to the barrel size, not the valve.


Are there any restrictions in THAT direction ?

I built a 1-1/4" piston valve.

Approximately 1" restriction at the barrel end of this thing.

Is something going to go "blooie", if I fit it with say a 1/2" barrel ?
  • 0

If you can't fix it, you don't own it.

Selador
2nd Lieutenant
2nd Lieutenant
 
Posts: 213
Joined: Wed Nov 03, 2010 9:44 pm
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Fri Nov 12, 2010 3:23 am

Oxbreath wrote:Is something going to go "blooie", if I fit it with say a 1/2" barrel ?


Assuming it's attached securely you shouldn't have any problems.
  • 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: Technician1002 » Fri Nov 12, 2010 10:46 am

I screw on a 1/2 inch barrel on my Marshmallow Cannon which is a piston valve with a 1 inch orifice. I shoot mini marshmallows, jawbreakers, and AA batteries. No problems.

Batteries shot from 1/2 inch barrel with a 1 inch valve.
Image

I have found when using a larger valve, a larger barrel and sabot for the smaller projectile works very well.

AA battery shot from a 2-1/2 inch barrel on a 2 inch valve.
Image

Sometime later I'll test AA batteries in a 1 or 1.25 inch barrel on the 1 inch valve Marshmallow Cannon to compare various barrel/sabot sizes on the 1 inch valve.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: Selador » Fri Nov 12, 2010 12:50 pm

I didn't think there would be a problem.

But you never know.

So I thought I'd check with the collective wisdom of experience, here.

Thank you.

:D
  • 0

If you can't fix it, you don't own it.

Selador
2nd Lieutenant
2nd Lieutenant
 
Posts: 213
Joined: Wed Nov 03, 2010 9:44 pm
Reputation: 0

Return to Pneumatic Cannon Discussion

Who is online

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

Reputation System ©'