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 53 users online :: 4 registered, 0 hidden and 49 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

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

The Team
Administrators
Global Moderators
global_moderators.png CS

pop-off

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

pop-off

Unread postAuthor: soka » Mon Oct 18, 2010 6:45 am

Hello ,hell!! i have some problems with a pop-off valve i tried to make. Usualy i ask people of my country's website ,patator.forum but we dont manage to find the solution.

First of all the pop- off is working , with a ball valve a litle opened but without the qev. You can see that in my video:

http://www.youtube.com/watch?v=IDnjK3RFPdM


With the Qev , it shots but when i close the gun. I dont know i have tried with many ball-valve in differents places but its never worked.

http://www.youtube.com/watch?v=wC_X_MzNEOY

Thanks if someone could help me, :) nice day to all of you!
(i dont know how to put the video here instead of the link, sory)
  • 0


soka
Private
Private
 
Posts: 17
Joined: Sun May 16, 2010 11:37 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Mon Oct 18, 2010 7:00 am

Great job on the farting machine :) Y

Your exhaust hole is too far away from the piston seat:

Image

Try drilling another one further down and it should do the trick.

Some links to similar homemade pop-offs I've made which could be useful:

Modified pop-off valve

custom pop-off v1.0

custom pop-off v2.0

custom pop-off v3.0
  • 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: soka » Mon Oct 18, 2010 7:10 am

Ok, thanks, in fact this think (my pop-off) was an air cylinder before, its for that reason it is very big. :?
I am gone to try with a hole at the bottom , thanks dude :)

LOL the farting machine!! :) , (with an audio amplificator it could be hard)

And thanks for your links all your pop_off are great, i had seen your vid on youtube before creating mine.

Other think, the guy who build that is registered on this forum? i am very curious about it, i would like to see the topic ,if one exist... :D
http://www.youtube.com/watch?v=_xGRn_hGFLo
  • 0


soka
Private
Private
 
Posts: 17
Joined: Sun May 16, 2010 11:37 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Mon Oct 18, 2010 8:39 am

soka wrote:Other think, the guy who build thatis registered on this forum? i am very curious about it, i would like to see the topic ,if one exist... :D


The user is registered as "Cannibal Corpse" and the thread about that project is here ;) It's a blowback hammer valve, the mechanism has nothing to do with pop-offs or pop-off piloted pistons.
  • 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 » Mon Oct 18, 2010 11:55 am

On a pop off valve the port is far away from the seat. Here is the theory.. Instead of thinking small full auto pilot areas for the theory, think of the original application, large air tank.

I modified the drawing to show the main important dimensions. When closed the small diameter near the inlet is the only area the the tank pressure pushes on. When the tank pressure rises too high, this valve seat cracks open and a larger diameter is exposed. The larger diameter does not seal, but acts as a sail in the discharge path lifting the valve near the ports near the other end of the cylinder. Two styles of ports are popular, ports out the side and for steam, port out the end to direct the flow away from the boiler and people, so the open end is oriented skyward. This flow holds the valve open. When the pressure drops and the flow is no longer high enough to float the valve in the open position, it sinks back toward the seat. When it gets close to the seat it begins to interfere with the flow, reducing it further, the sail fails to hold the valve open and it pops back closed. This is why they pop open and pop closed.

If you wish to modify a compressor pop off valve, the "sail" area can be altered to change the pressure the valve can re-close. Taking apart a compressor pop off and soldering a extra wire rim on the sail can cause it to remain open longer without changing it's flow when open as the flow when open is set by the valve seat orifice size.

I learned this when studying steam engines and building some for the boiler for models. There is a science to setting the ratio of a pop off valve.
  • 0

Attachments
effectivepopoffconfig_102.gif
effectivepopoffconfig_102.gif (2.36 KiB) Viewed 438 times
User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: jackssmirkingrevenge » Tue Oct 19, 2010 4:27 am

Tech, what you posted is conceptually identical to mine, the main point is that the exhaust port is always exposed even with minimal piston movement, otherwise it's farting machine all the way.

The difference is that mine is not intended as a pilot but as a primary valve and has a sealed piston, so the air goes directly to the port without losing pressure by expanding in the area behind the piston before exhausting, and it also means there is no air pressure behind the pressure attempting to equalise the forces opening the piston ensuring a more effective "pop".
  • 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: POLAND_SPUD » Tue Oct 19, 2010 5:20 am

forget about pop-off valve for fullauto. Either use a solenoid valve + time relay or a pneumatic time delay valve.
  • 0

Children are the future

unless we stop them now
User avatar
POLAND_SPUD
Chief of Staff
Chief of Staff
 
Posts: 5405
Joined: Sat Oct 13, 2007 4:43 pm
Country: Israel (il)
Reputation: 10

Sponsored

Sponsor
 


Unread postAuthor: jackssmirkingrevenge » Tue Oct 19, 2010 5:48 am

POLAND_SPUD wrote:forget about pop-off valve for fullauto.


What, it works mate! :P :D
  • 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: lozz08 » Tue Oct 19, 2010 6:55 am

Why do you dismiss the rattlesnake valve poland? What could be better for full auto in terms of efficiency, adjustability, everything? It's just not that easy to build.
  • 0

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

Unread postAuthor: jackssmirkingrevenge » Tue Oct 19, 2010 7:21 am

lozz08 wrote:Why do you dismiss the rattlesnake valve poland?


Because he has no concept of simplicty and loves to contradict me ;)

It's just not that easy to build.


There was talk of converting a QEV, it could work if made like this:
  • 0

Attachments
untitled.GIF
untitled.GIF (19.06 KiB) Viewed 334 times
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

Return to Pneumatic Cannon Discussion

Who is online

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

Reputation System ©'