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 71 users online :: 5 registered, 0 hidden and 66 guests


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

Registered users: Bing [Bot], 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

Pilot Volume - not really variable

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

Unread postAuthor: jackssmirkingrevenge » Thu Oct 25, 2007 3:43 am

agreed with the above re pistons in a T
  • 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: octane89 » Thu Oct 25, 2007 10:04 am

Ok, I have a 3" tee and will have a 1.5" port. So the travel would be .375 with the d/4 equation or .58 (or .59 if I round up a hundreth) with the travel=pi*r^2/w equation. That helps significantly, thanks again.
  • 0

User avatar
octane89
1st Lieutenant
1st Lieutenant
 
Posts: 257
Joined: Tue Sep 11, 2007 1:20 pm
Reputation: 0

Unread postAuthor: sanaka » Fri Oct 26, 2007 2:12 am

So, this issue (the pilot volume one) keeps sloshing back and forth in my mind. What BC said makes sense. So does what clide said. I think the stuff I originally posted applies, yet minimizing volume makes sense.

I think the ideal is kind of a paradox: minimal volume with maximum flow. A tiny little pilot volume exiting through a big honkin' valve opening.

The following shall be some ramblings on this subject, relatively unencumbered by the thought process:

I think to locate the trigger somewhere convenient, we end up using a 'normal' size air hose like 1/4" or so. This is small enough to actually impede the flow that would be ideal for emptying the pilot, since we would prefer it to empty instantaneously. Hence the smaller the volume of air that needs to exit the pilot, the faster the valve will trigger.

Even if we increase the hose size massively enough to eliminate the impedance, the same bottleneck will happen at the valve unless we equally increase the valve opening.

Then even if we do that, the bigger valve is going to take longer to open. No matter what kind it is, a valve takes time to open, so a bigger one takes more time. So the pilot will start emptying before the valve is fully open, which is very much like if the valve opening were smaller, so the same bottleneck will apply to some degree.

All in all, I think this is in fact a fairly involved fluid mechanics problem, the best solution to which would, like most real world problems, involve careful compromises and tradeoffs to optimize what can be done against perfect theory.

My gut feeling is also that many of the setups people are actually using in fact do a good job addressing the real world limitations and achieve this optimization quite well.

I thought I was going to get to work on a spudgun tonight, but alas, no. Was on the job 'til 6:30 and I'm pretty whipped. Want to hear something cool, though? My work partner, whom I've been sharing a bit with about this whole projectile thing, returned to the job today after a parts run and said "Look what I found in the irrigation aisle at Lowe's" and handed me a printed out page from Spudtech! Someone was shopping parts for a tennis ball launcher! It was cool.

Peace,
Sanaka
  • 0


sanaka
Private
Private
 
Posts: 8
Joined: Wed Oct 10, 2007 7:53 am
Reputation: 0

Unread postAuthor: octane89 » Fri Oct 26, 2007 7:43 am

Well in some cases, when you decrease the pilot volume, you will limit the travel of a piston. Like in my case with a 3" tee which in turn brings up the real world limitations you mentioned. Regadless this now has me thinking of new ways to pilot a valve and such.
  • 0

User avatar
octane89
1st Lieutenant
1st Lieutenant
 
Posts: 257
Joined: Tue Sep 11, 2007 1:20 pm
Reputation: 0

Previous

Return to Pneumatic Cannon Discussion

Who is online

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

Reputation System ©'