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M4 SOPMOD airgun/replica

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: maverik94 » Sat Jan 09, 2010 11:55 am

That's no secret, I've been an Evangelical Epoxist since the SpudTech days

HAHA, Classic
is it possible for a homemade QEV to take 30 bar?

If built from the right materials with the right pilot, you can make your piston valve (QEV) to nearly any pressure, (Within Reason).
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Unread postAuthor: POLAND_SPUD » Sat Jan 09, 2010 12:10 pm

is it possible for a homemade QEV to take 30 bar
yes... thought they are normally refereed to as piston valves here...

operating pressure it goes from 2-10 bar
basically all QEVs (ready made piston valves) are rated to 10 bar max though they are normally used at 30 bar and more

poniklani mesing
that's nickled brass right ?? I think that you can expect it to handle high pressures well

you might consider contacting the companies which might have it directly and ask if they have QEVs... if that fails I might even buy one here and send it to you... or ask some companies if they mind directly shipping stuff abroad
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Unread postAuthor: FighterAce » Sat Jan 09, 2010 12:52 pm

POLAND_SPUD wrote:
is it possible for a homemade QEV to take 30 bar
yes... thought they are normally refereed to as piston valves here...

operating pressure it goes from 2-10 bar
basically all QEVs (ready made piston valves) are rated to 10 bar max though they are normally used at 30 bar and more

poniklani mesing
that's nickled brass right ?? I think that you can expect it to handle high pressures well

you might consider contacting the companies which might have it directly and ask if they have QEVs... if that fails I might even buy one here and send it to you... or ask some companies if they mind directly shipping stuff abroad


Poniklani mesing is nickled brass yes.

That store is not in my city so I dubit they will be able to send it over here. And I think they make stuff for industrial use only...
I just sent them an E-mail so we'll see :D

Thats very generous of you... but even if I dont find something I'll make my own cause I already have all the parts.
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 09, 2010 2:41 pm

FighterAce wrote:is it possible for a homemade QEV to take 30 bar?


I've taken mine to 55 bar ;)
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Unread postAuthor: FighterAce » Sat Jan 09, 2010 2:52 pm

jackssmirkingrevenge wrote:
FighterAce wrote:is it possible for a homemade QEV to take 30 bar?


I've taken mine to 55 bar ;)


jesus... what do you shoot? elephants?

I just tested my new piston and it seemed to move freely inside the 3/4 connector but when I pressurise it, it wont open untill the pressure is like 1 bar... its like the air just wants to out the plot valve and ignores the piston..
any idea whats causing this?
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 09, 2010 3:03 pm

FighterAce wrote:jesus... what do you shoot? elephants?


Stick around this forum, you'll realise that MOAR POWER! doesn't need a reason, it's a way of life ;)

its like the air just wants to out the plot valve and ignores the piston..
any idea whats causing this?


Typical reasons are:

- piston too loose - moar air is leaking around the piston than can escape from the pilot valve

- piston diameter too close to barrel diameter
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Unread postAuthor: psycix » Sat Jan 09, 2010 3:19 pm

- piston diameter too close to barrel diameter

This is not a problem on its own, it just amplifies the "piston too loose" problem.

With an o-ringed piston, your piston diameter may be 99% of the barrel diameter and work superb.
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Unread postAuthor: FighterAce » Sat Jan 09, 2010 3:20 pm

jackssmirkingrevenge wrote:
its like the air just wants to out the plot valve and ignores the piston..
any idea whats causing this?


Typical reasons are:

- piston too loose - moar air is leaking around the piston than can escape from the pilot valve

- piston diameter too close to barrel diameter


yep the piston is pretty loose... when I finished working with the dremel it was perfect but I over did it with sand paper

my barrel has the same diameter as the piston but I dont see the connection... but witch one inner or outer?

can you recommend some other piston material maybe? I know wood could work but I dont have the time and hot glue is all sticky and absorbs the lubrication so its out aswell...
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 09, 2010 3:29 pm

FighterAce wrote:my barrel has the same diameter as the piston but I dont see the connection... but witch one inner or outer?


Unless you're using an extremely tight piston, it's a good idea to have the outer diameter of the piston to be substantially bigger than the inner diameter of the barrel. Try wrapping your piston in duct or masking tape and see if it makes a difference.

can you recommend some other piston material maybe? I know wood could work but I dont have the time and hot glue is all sticky and absorbs the lubrication so its out as well...


Sure ;)
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Unread postAuthor: psycix » Sat Jan 09, 2010 3:32 pm

my barrel has the same diameter as the piston but I dont see the connection... but witch one inner or outer?

That is a common error.
I recommend you to go to the "piston valves explained visually" thread to learn how piston valves work.
A piston needs frontal area for the pressure to push on before starting to move. The barrel needs to be smaller then the piston, the piston seals onto the porting.

With a big gap between the piston and the tube it slides in, a barrel diameter close to the piston diameter amplifies this problem.
Make the piston 25-50% larger then the barrel for a reliable valve.
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Unread postAuthor: FighterAce » Sat Jan 09, 2010 3:42 pm

ahh you mean that barrel... I'm using a 3/4 adapter for the garden hose/gun
and its definitely 50% smaller then the piston face

I'm giving hot glue another go, trying another lubricant that the hot glue wont absorb... hopefully

EDIT
still getting alot more kick out of the pilot valve then the piston valve with the new piston... I molded it from the connector so it really is a tight fit...
there must be some other problem
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 09, 2010 5:01 pm

What are you using as a pilot valve? Also, how much space is there behind the piston?

Effectively the piston only needs to move 25% of the barrel diameter for full flow, though you should allow a bit more to account for piston bounce. This means that for a 3/4" barrel, 5-10mm of movement is enough.
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Unread postAuthor: FighterAce » Sat Jan 09, 2010 5:40 pm

jackssmirkingrevenge wrote:What are you using as a pilot valve? Also, how much space is there behind the piston?

Effectively the piston only needs to move 25% of the barrel diameter for full flow, though you should allow a bit more to account for piston bounce. This means that for a 3/4" barrel, 5-10mm of movement is enough.


As a pilot valve I'm using a 1/2 ball valve. I was hoping to make the piston so sensitive that I could trigger it with a schrader valve to avoid having valve handles and therefore making a better air gun replica...

Behind the piston theres about 70mm to the ball valve.
My piston has like 20mm of movement.... so I gotta find a barrel with longer threads and then sand some threads off so it can go in deeper to acheve 10mm. When I do that, the piston will be more stable because more of its length will ride inside the connector making a better seal?

EDIT
I made a longer piston and it worked. All I have to do is open the ball valve quick enough so the piston can move. If I open it slowly it will all leak out. Any suggestions how to fine tune it?
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