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 27 users online :: 5 registered, 0 hidden and 22 guests


Most users ever online was 106 on Sat Jun 14, 2014 4:35 pm

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], nibbler125, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Idea for metal piston valve.

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: MrCrowley » Thu Jun 21, 2012 12:18 am

D_Hall wrote:
MrCrowley wrote:Piston hybrids are more difficult to build seeing as they require o-rings to isolate the pilot area.

Not necessarily. Or at least, I hope not as I'm preparing to build one sans o-rings to isolate the pilot area.
Well of course there are exceptions :wink: They (o-ring hybrid pistons) are not exactly difficult to build if you have a lathe or similar machining equipment either.

Looking forward to seeing what you end up building; with a record like yours, it should be pretty great. Any reason you want to use an o-ringless design? Apart from reducing maintenance and possible things that could go wrong, are there any other reasons?

Edit: I'd rather you go with the labyrinth method over o-rings as it would bring about a new 'development' in hybrid construction. I'm just asking why you're doing it out of curiosity.
  • 0

Last edited by MrCrowley on Thu Jun 21, 2012 3:21 am, edited 1 time in total.
User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10167
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: Crna Legija » Thu Jun 21, 2012 3:05 am

Dam mate I was learning area in grade 5.

But yeah search Lnl made a spread sheet that will do the calculations for you. Find it and you good to go, i know where it is but ill let you find it.
  • 0

'' To alcohol... The cause of, and solution to, all of life's problems.”
--Homer Simpson

Add me on ps3: wannafuk, 8/11/11 cant wait
User avatar
Crna Legija
Major General
Major General
 
Posts: 2333
Joined: Sun Jul 20, 2008 5:14 am
Location: australia
Reputation: 0

Unread postAuthor: 8tonsemi » Thu Jun 21, 2012 7:57 am

If I'm correct mcr45 mix numbers are 1x mix of mapp gas equals .71 and air equals 13.9 psi of air for a 1x mix. Let me know if it's right or wrong.
  • 0

User avatar
8tonsemi
Captain
Captain
 
Posts: 321
Joined: Thu Feb 16, 2012 6:08 pm
Location: The moon
Reputation: 0

Unread postAuthor: D_Hall » Thu Jun 21, 2012 9:25 am

MrCrowley wrote:Any reason you want to use an o-ringless design? Apart from reducing maintenance and possible things that could go wrong, are there any other reasons?

Nope. You nailed it for the most part. I figure fewer things to go wrong, no maintenance, a piston that moves more smoothly, and maybe even a slightly lighter weight piston since the grooves for a labyrinth seal need not be as deep.

Edit: I'd rather you go with the labyrinth method over o-rings as it would bring about a new 'development' in hybrid construction.

In the 'development' sense I'm doing several things that I think are new although I confess that I've not done extensive reading to ensure of that. Maybe others have done it this way. I dunno. I'm just doing it this way because it seems the "right" way to do it.

Concept of operation....

0) Gun's basic configuration appears to be that of an old school pneumatic coaxial. There are some differences, but that's close enough for this conversation. Also note that there are check valves connecting the pilot area to the combustion chamber (with flow being allowed from the pilot to the chamber).

1) Barrel sealing piston valve is open. Using a metering pipe, propane is injected into the pilot volume. (If all goes well) the propane drives the piston forward to close the valve and more or less just sits there in the pilot although some will certainly leak to the main combustion chamber either around the labyrinth seal or through the check valves.

2) High pressure air (also from a metering pipe), is injected into the pilot volume. The air mixes with and drives the propane out of the pilot area and into the combustion chamber. At first, the mixture in the pilot will (obviously) be very rich, but as the process continues you should end up with essentially air (yes, there will be a bit of contamination) in the pilot volume and a combustible mixture in the combustion chamber.

3) From there, operation is just like any other valved hybrid with one exception... As the piston moves backwards as the valve opens, the pressure in the pilot area will obviously increase. At the same time (or ever so slightly afterward if you want to split hairs), pressure in the chamber will be falling. When the pressure in the pilot exceeds the pressure in the chamber, air from the pilot is vented into the chamber thereby giving a teeny tiny, probably not even measurable boost to the power of the gun as the energy contained in the pilot volume is sent down the barrel rather than being wasted.

Mind you, the "pilot boost" is minimal at best. I just figured, "Hey, why not vent it somewhere where it *might* be useful?" And as a bonus, the gun should be ever so slightly quieter to the user.

4) Oh, and the whole mess will be quasi automated so that while you're aiming/shooting, the metering pipes are refilled.


edit: Upon a re-read... Two more points....

a) When I quoted you, I meant to emphasize the "o-ring required" not the "difficult to build" aspect of your quote. I agree that o-rings aren't difficult. I disagree that they're required.

b) Sadly, I don't have regular access to a lathe and such so construction will take a long time (gotta call in favors and the like). I figure I'm at least a year out even if it won't take but 20 man hours to build.
  • 0

Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
D_Hall
Donating Member
Donating Member
 
Posts: 1721
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Reputation: 2

Unread postAuthor: MrCrowley » Thu Jun 21, 2012 2:27 pm

8tonsemi wrote:If I'm correct mcr45 mix numbers are 1x mix of mapp gas equals .71 and air equals 13.9 psi of air for a 1x mix. Let me know if it's right or wrong.
Well the air will depend on where you live and such; here it's closer to 14.5PSI I believe. You can find this information in your local weather report as the barometric pressure. Also, you wont be 'injecting' any air in a 1x mix, only a 2x mix and beyond.


@D_Hall,

I've always wondered about trying what you're doing in steps 1 & 2 as it is a far more time efficient way to fuel. Step 3 is quite interesting and even if it has no discernible effect, it'll be another concept that has been put in to practice.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10167
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: D_Hall » Thu Jun 21, 2012 3:02 pm

MrCrowley wrote:
8tonsemi wrote:If I'm correct mcr45 mix numbers are 1x mix of mapp gas equals .71 and air equals 13.9 psi of air for a 1x mix. Let me know if it's right or wrong.
Well the air will depend on where you live and such; here it's closer to 14.5PSI I believe. You can find this information in your local weather report as the barometric pressure. Also, you wont be 'injecting' any air in a 1x mix, only a 2x mix and beyond.

Depends upon how you define 1X.

I personally have stood my ground that 1X = 1 *standard* atmosphere and believe that anything else is stupid. After all, if 1X means something different for every person, then it doesn't mean anything at all! Fixing it at 1X *standard* atmospheric conditions gives it universal meaning. With all that said, here at 2300 ft ASL, I most certainly do inject air for a 1X mix.
  • 0

Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
D_Hall
Donating Member
Donating Member
 
Posts: 1721
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Reputation: 2

Unread postAuthor: MrCrowley » Thu Jun 21, 2012 3:04 pm

Sorry, I may have lost you on the terminology here (my fault, not yours) but aren't we describing the same thing: 1x mix = normal combustion cannon (atmospheric air + injected fuel)?
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10167
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Sponsored

Sponsor
 


Unread postAuthor: 8tonsemi » Thu Jun 21, 2012 3:21 pm

So where you live a 2x mix is 29psi of air?
  • 0

User avatar
8tonsemi
Captain
Captain
 
Posts: 321
Joined: Thu Feb 16, 2012 6:08 pm
Location: The moon
Reputation: 0

Unread postAuthor: D_Hall » Thu Jun 21, 2012 3:46 pm

MrCrowley wrote:Sorry, I may have lost you on the terminology here (my fault, not yours) but aren't we describing the same thing: 1x mix = normal combustion cannon (atmospheric air + injected fuel)?


Not in my book. 1x mix = normal combustion cannon only if you live at sea level. For any other altitude a normal combustion cannon is going to be some number <1X. For me? That would be about... 0.93X.
  • 0

Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
D_Hall
Donating Member
Donating Member
 
Posts: 1721
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Reputation: 2

Unread postAuthor: D_Hall » Thu Jun 21, 2012 3:49 pm

8tonsemi wrote:So where you live a 2x mix is 29psi of air?


I would argue that a 2X mix should be 14.7*2 = 29.4 psia of pre-ignition gases REGARDLESS of where you live.

For extra credit, you can correct for temperature (which in practice, I do), but how damned hard is it to make standard atmosphere corrections? It isn't!
  • 0

Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
D_Hall
Donating Member
Donating Member
 
Posts: 1721
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Reputation: 2

Unread postAuthor: 8tonsemi » Thu Jun 21, 2012 3:59 pm

So your saying it doesn't matter where you live just keep it standard.
  • 0

User avatar
8tonsemi
Captain
Captain
 
Posts: 321
Joined: Thu Feb 16, 2012 6:08 pm
Location: The moon
Reputation: 0

Unread postAuthor: MrCrowley » Thu Jun 21, 2012 4:12 pm

Ah, I see what you mean. Not a bad idea I guess.

Edit: 8ton, he's saying we should have a standard figure for 1x and you modify that number as a percentage based on where you live. If your local atmospheric pressure is .95 that of 14.7psi, you state your mix as a 0.95x. A problem is that it may lead people to believe you haven't fueled the correct amount for whatever reason.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10167
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: 8tonsemi » Thu Jun 21, 2012 4:27 pm

Where I live the pressure is 29.8 I thik. That seems high. Should I still use that and how does that efect the fuel charge
  • 0

User avatar
8tonsemi
Captain
Captain
 
Posts: 321
Joined: Thu Feb 16, 2012 6:08 pm
Location: The moon
Reputation: 0

Unread postAuthor: MrCrowley » Thu Jun 21, 2012 4:42 pm

29.8 inHg? I think that's about 14.5psi, check google.

Edit: I live at sea level where the current pressure is ~1020 hectopascals, so the rest of the forum can make their mind up as it doesn't affect me :D
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10167
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: 8tonsemi » Thu Jun 21, 2012 6:31 pm

The fuel charge is still 7.1PSI for 10x mix right and 2x mix= 1.42PSI? And the meter is going to be 1/10th of the volume of the chamber?
  • 0

User avatar
8tonsemi
Captain
Captain
 
Posts: 321
Joined: Thu Feb 16, 2012 6:08 pm
Location: The moon
Reputation: 0

PreviousNext

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], nibbler125, Yahoo [Bot]

Reputation System ©'