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 80 users online :: 5 registered, 0 hidden and 75 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 vs Piston Weight

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

Pilot Volume vs Piston Weight

Unread postAuthor: goose_man » Thu Oct 25, 2007 12:08 am

In several topics involving pistons, people often suggest drilling out the back to make the piston lighter and therefore increase performance. One problem: this increases pilot volume. I'm wondering if the lowered weight of the piston more than compensates for the increased pilot volume (assume no filler is added to back of piston; ie. foam), or whether drilling the piston is not just only a waste of effort but actually decreases performance.

Obviously this depends on many things including piston weight (or density) before drilling, amount of pilot volume before drilling, and other factors. Has anyone actually observed a significant change in performance by drilling out the back of the piston? If so, was it an increase or decrease, and what were the other variables (pilot volume before and after, piston wieght before and after, piston diameter, o-ringed or not, etc.)?

-goose_man
  • 0

User avatar
goose_man
Sergeant First Class
Sergeant First Class
 
Posts: 134
Joined: Sun Apr 08, 2007 6:37 am
Reputation: 0

Unread postAuthor: hi » Thu Oct 25, 2007 1:00 am

in my personal opinion, a piston valve open so fast it doesnt really matter if you are off by 1/4'' or if its 1 oz. more than ideal. obviously if it was solid steel then there would be a problem, but most pistons i dont think weigh enough to matter. i think that friction would decrease performance more than weight of the piston (i.e. put some lube on it and it will work really well)
  • 0

"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
User avatar
hi
Major General
Major General
 
Posts: 1619
Joined: Thu Feb 01, 2007 9:28 pm
Reputation: 0

Unread postAuthor: clide » Thu Oct 25, 2007 1:09 am

Piston weight or pilot volume typically don't have any significant affect on performance. The biggest advantage of a lighter piston is that it is easier to stop so it puts less stress on the gun.
  • 0


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

Unread postAuthor: battlemonkey » Thu Oct 25, 2007 2:58 am

True clide. You dont want your piston blowing out the back of the cannon like MrCrowly's piston cannon. I would go for lighter but thats just me
  • 0

User avatar
battlemonkey
Sergeant First Class
Sergeant First Class
 
Posts: 137
Joined: Sat Sep 22, 2007 3:42 pm
Reputation: 0

Unread postAuthor: MrCrowley » Thu Oct 25, 2007 3:03 am

Haha yeah thanks for that battlemonkey :P

My piston isn't exactly light, hence the failing of the PVC fittings even though I did have a bumper.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: goose_man » Thu Oct 25, 2007 7:48 am

clide wrote:Piston weight or pilot volume typically don't have any significant affect on performance. The biggest advantage of a lighter piston is that it is easier to stop so it puts less stress on the gun.


Ah, I see. I wonder how fast the piston actually moves though...

-goose_man
  • 0

User avatar
goose_man
Sergeant First Class
Sergeant First Class
 
Posts: 134
Joined: Sun Apr 08, 2007 6:37 am
Reputation: 0

Unread postAuthor: ALIHISGREAT » Thu Oct 25, 2007 8:09 am

why don't you just make a light low friction piston wih a tiny pilot volume?
  • 0

User avatar
ALIHISGREAT
Major General
Major General
 
Posts: 1779
Joined: Sat Aug 25, 2007 6:47 pm
Location: UK
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: hyldgaard » Thu Oct 25, 2007 8:27 am

ALIHISGREAT wrote:why don't you just make a light low friction piston wih a tiny pilot volume?


Isn't that what we are all trying to do? :wink:
  • 0

User avatar
hyldgaard
Sergeant Major
Sergeant Major
 
Posts: 187
Joined: Tue Sep 25, 2007 4:21 am
Location: Denmark
Reputation: 0

Unread postAuthor: ALIHISGREAT » Thu Oct 25, 2007 9:06 am

ooops :oops: didn't read t properly. i think the best way would be to drill it out but have a plug or cap over the hole to keep the pilot volume low.
  • 0

User avatar
ALIHISGREAT
Major General
Major General
 
Posts: 1779
Joined: Sat Aug 25, 2007 6:47 pm
Location: UK
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Thu Oct 25, 2007 9:11 am

Piston weight or pilot volume typically don't have any significant affect on performance. The biggest advantage of a lighter piston is that it is easier to stop so it puts less stress on the gun.


I disagree there. The heavier a piston, the slower it will accelerate and you can't deny the link between valve opening time and performance. Also, the lower the pilot volume, the quicket the pilot chamber will depressurise and the quicker the piston will start to move.
  • 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: unisonmind » Thu Oct 25, 2007 10:08 am

so in the end what you want is a light piston and a small pilot volume cuz the lighter the piston=faster it will accelerate. the smaller the pilot volume the quicker the pilot volume is exhausted=the faster the piston will start to move

so in the end you want both so they can work together to open your valve faster

open faster = more power
  • 0

THE DIFFERENCE BETWEEN A FLOWER AND A WEED IS A JUDGEMENT
User avatar
unisonmind
Staff Sergeant
Staff Sergeant
 
Posts: 118
Joined: Wed Jan 24, 2007 9:25 pm
Reputation: 0

Unread postAuthor: boilingleadbath » Sat Oct 27, 2007 10:35 pm

I'd argue that the system is complex enough that it's hard to make hard-and-fast predictions about performance.

Indeed, I've modeled situations with the GGDT in which a larger pilot volume improved muzzle velocity. (said situation was reasonable)

And there probably are scenarios where a heavier piston would increase performance.
  • 0

User avatar
boilingleadbath
Moderator
Moderator
 
Posts: 1642
Joined: Sat Mar 12, 2005 10:35 pm
Location: Pennsylvania, USA
Reputation: 0

Unread postAuthor: ammosmoke » Sat Oct 27, 2007 11:25 pm

Isn't possible that GGDT just glitched a bit? I mean, the program is definitely not perfect...
  • 0

<img>http://www.speedtest.net/result/309559995.png</img>
User avatar
ammosmoke
Brigadier General
Brigadier General
 
Posts: 1011
Joined: Wed Sep 27, 2006 10:57 am
Reputation: 0

Unread postAuthor: MrCrowley » Sat Oct 27, 2007 11:51 pm

boilingleadbath wrote:I'd argue that the system is complex enough that it's hard to make hard-and-fast predictions about performance.

Indeed, I've modeled situations with the GGDT in which a larger pilot volume improved muzzle velocity. (said situation was reasonable)

And there probably are scenarios where a heavier piston would increase performance.


I've also noticed that, a pilot volume of 50cm^3 and 250cm^3 has no effect on velocity or anything according to GGDT with some stuff I've modeled, even changing pilot valve flow and other parameters I get no change sometimes.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: spudgunnerwryyyyy » Sat Oct 27, 2007 11:55 pm

Well how does ggdt model the piston, because in Mr. Crowleys case his piston doesn't fit perfectly just well. But is dan300 or sgort87 modeled there pistons with o-rings the performance would be different even though ggdt doesn't consider the design of the piston just weight. but not if there are o-rings which as you all know is a pretty big factor.
  • 0

The Doors are awesome, Led Zeppelin is amazing, and Motley Crue kicks @$$.
Go Orange Box

RAP SUCKS
User avatar
spudgunnerwryyyyy
1st Lieutenant
1st Lieutenant
 
Posts: 261
Joined: Thu Jul 12, 2007 10:54 pm
Reputation: 0

Next

Return to Pneumatic Cannon Discussion

Who is online

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

Reputation System ©'