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Problème full auto !

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Problème full auto !

Unread postAuthor: smirpab » Tue Jan 25, 2011 2:01 pm

Hello to you!

First of all, saddened for my English, I am French ;)

I wanted to have some piece of information on pac full house automobile, I am on the conception of one, but it is not an easy thing...

I block especially on the pop off, I describe you my problem:

- on almost quite pop off which I have, arrived at a certain pressure or below debit of air, they avoid...

- I had read that the relation enters the IC of the pop off and the environment of holes of escape of that this must be equal to the external diameter of its piston(valve)?

Here we are, thank you for helping me:)

En français :

Bonjour à vous !

Tout d'abord, désolé pour mon anglais, je suis français ;)

Je voulais avoir quelque renseignement sur des pac full auto, je suis sur la conception d'un, mais ce n'est pas une chose facile ...

Je bloque surtout sur la pop off, je vous en décris mon problème :

-sur presque toute les pop off que j'ai, arrivé à une certaine pression ou en bas débit d'air, elles fuient ...

-J'avais lu que la relation entre le CI de la pop off et le milieu du trous d'échappement de celle ci doit être égale au diamètre externe de son piston ?

Voilà, merci de bien vouloir m'aider :)
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Unread postAuthor: jrrdw » Tue Jan 25, 2011 2:45 pm

Kinda hard to figure out what your asking. If I'm correct, you want to know how the "pop off valve" works with full auto.

In a full auto setup the pop off valve is set to a determined pressure and acts as the pilot. When the desired pressure is reached the pop off valve vents the pilot actuating the piston and fires the gun.

Someone correct me if I'm wrong, but I think I got that right.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 2:56 pm

Are you looking to have the pop-off valve as a pilot valve or as the main valve?

In the latter case, the valve must have the following features to work successfully:

- piston diameter significantly larger than piston seat

- if the piston is airtight, then the exhaust port should be exposed even when the piston is closed (like so)

- the exhaust porting diameter should be significantly smaller than the piston seat, in order to allow pressure buildup that causes the piston to "pop".
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Unread postAuthor: smirpab » Tue Jan 25, 2011 3:18 pm

In fact, I already have to test pop off inconvenient and pop off home made;)

But my problem, it is because in a certain pressure / debit, they begin avoiding...

If my IC is 8/6 and my piston(valve) of 12mm, that squeezed being enough enough according to you?

My piston must be hermetic in the body?
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Unread postAuthor: jrrdw » Tue Jan 25, 2011 3:41 pm

We need some help with translation. Are you using Google translator?
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Unread postAuthor: smirpab » Tue Jan 25, 2011 4:22 pm

I use Reverso ;)
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 4:34 pm

Can you ask someone like CpTn_lAw to help you with translating? As you might know I've made several of these pop-off thingies and I'm sure we can help you.
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Unread postAuthor: CpTn_lAw » Tue Jan 25, 2011 4:53 pm

Oki doki.....CpTn to the rescue!

He is trying to make a full-auto gun, and thus trying to figure out them. His main concern is about the pop-off, wich i guess all of you understood. He wants to know If the piston must be completely airtight, and something regarding the IC? wich i don't know what it is...
His pop-off is leaking when the pressure is almost at popping level, or when the flow of air is small.

@smirpab : la pop-off doit vraiment faire "pop!" , elle doit attendre la pression désirée et laisser tout d'un coup sortir.



Edit : go take a look at http://www.spudfiles.com/forums/the-slingshot-channel-thread-t19034,start,885.html pleeeeeeeeaase!!!
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Unread postAuthor: smirpab » Tue Jan 25, 2011 5:07 pm

@CpTn_lAw: Oui, mais le problème, c'est quand je tire entre 10/6bars, elle fait bien "pop", mais arriver en bas débit d'air ou de pression, elle fuit un pschiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiit .

En tout cas merci ;)
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 5:17 pm

Is the pop-off a man valve like this, or is it being used to pilot a piston valve/QEV?

mais arriver en bas débit d'air ou de pression, elle fuit un pschiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiit


Well, of course there's a minimum popping pressure - have you tried reducing the spring pressure?

Some pictures/diagrams would be really helpful.
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Unread postAuthor: saefroch » Tue Jan 25, 2011 5:53 pm

My french is not good enough to put this in french (Je suis en train d'apprendre le français.), but I can tell you that your translator (Reverso) needs some work. It translates désolé as the passé composé, ou l'imparfait. Try Google Translate. I've found that it is very good for writing french essays :wink:

So... I think the problem with your pop-off is that it doesn't have enough flow (it doesn't allow enough air past). Have you tried putting in more than 10/6 bar?
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 25, 2011 5:59 pm

saefroch wrote:Have you tried putting in more than 10/6 bar?


From what I understood, it works well at 10/6 bar then stops popping below that pressure - which is the sort of performance you'd expect, given that a pop-off valve needs a minimum pressure to operate...
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Unread postAuthor: jrrdw » Tue Jan 25, 2011 6:18 pm

CpTn_lAw wrote:and something regarding the IC


IC = Inside Circumference???
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Unread postAuthor: Crna Legija » Tue Jan 25, 2011 7:56 pm

i tryed to make a QEV pop off just for fun but it didn't work with a adjustable pop off valve i had to get a one that was pre set at 150 and cant be changed then it work fine.
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Unread postAuthor: smirpab » Wed Jan 26, 2011 7:12 am

Well yes, but I want to avoid it leaking at low speeds or low pressure ...

I need the info off of the pop off Brian the brain ;)
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