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1/2" or 3/4" QEV? Any REAL difference?

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.
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Unread postAuthor: Technician1002 » Wed Jul 01, 2009 6:45 pm

neeewwww wrote:@spudmanb3 - I were planning to use a 1" or 3/4" Ballvalve actuated by spring... So, going from a 3/4" or 1" BV to a 1/2" QEV wouldn´t be THAT perfomance gain or I´m wrong?



Performance gain or loss comparing a QEV and ball valve boils down to how fast can you open the valve? When open the ball valve beats the socks off a QEV because of a larger orifice and no bends in the flow.

In a ball valve the loss is due to the short distance from the breech to the muzzle. The projectile has left long before the valve is open very far, so most of the shot is done with a mostly closed valve. The advantages of a QEV start to shrink as you move to longer barrels with very large chambers. A small high pressure launcher has poor results compared to a QEV with the slow ball valve.

Even those with large cannons and long barrels have to find ways to get a ball valve open quickly to get reasonable performance.

This video is from one of our competitors in the Engineering Challenge. This cannon did not place. We beat them in a landslide with a faster valve.
[youtube]http://www.youtube.com/watch?v=ep88WGNja9c[/youtube]
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Unread postAuthor: Ragnarok » Wed Jul 01, 2009 6:56 pm

POLAND_SPUD wrote:@rag still that performance gain is less than 5% or so... so what's the point ?

To use a variant of the old saying: "It might only be worth a tiny amount, but that might be what makes the difference."

This is about high velocity efficiencies, and given my preference for cannons that hang around in the high subsonic velocities, it becomes increasingly important.
Besides, I'm not going to turn down a performance gain that costs me next to nothing.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: neeewwww » Fri Jul 03, 2009 12:56 pm

Final decision...

Here in Brazil, QEV are only avaliable to professionals... Of course you can buy just one QEV and use it at your cannon... But the price you need to pay for just ONE QEV is TOO high.

Brazil:
1/2" QEV - 60BRL or 30USD
3/4" QEV - 140BRL or 71USD

US/EUR:
3/4" QEV - 21USD

See the difference?

The estimated costs would be around: 250BRL or 130USD. (using 3/4" QEV).

Ok, I buy the valve, attach a barrel and chamber... and done...

BUT where´s the FUN? I like the DIY way... Thats why I´m planning to build a SpudGun and not buying an AirSoft.

Finally, thanks guys for your help... I really appreciate...

Homemade QEV (or french valve) here I go...

Cheers from South America x)

o>
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Unread postAuthor: Brian the brain » Fri Jul 03, 2009 2:44 pm

Thanks for picking my design! :D


Since you have contacted me through PM about this:

It would be cheaper for you to buy it in Brasil.You seem to forget about shipping costs.
I could send you a " cheaper" 1/2" qev...but you'd end up with double the cost 'cause of shipping...


And possibly difference in threads..1/2" bsp is different from 1/2" npt...
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: neeewwww » Fri Jul 03, 2009 3:11 pm

All right... all right YOUR design x)

I like shot-gun styles... and LOUD ones...

I know about all the tax, shipping costs... and whatever else...
Yeah.. It will be cheaper to buy the 1/2 or 3/4 here in Brazil, but not so cheap that I expected...

By the way I will go throught the DIY way...

Thanks.

o>
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Unread postAuthor: Brian the brain » Sat Jul 04, 2009 5:43 am

That's not what I meant by my design.

I really like the fact you want to build one.

I wasn't claiming credit..I just feel " honored" you like the design.
Text can sometimes come across the wrong way.. :wink:

A Tee with the bottom section in a smaller diameter will help to get the chamber closer to the barrel.It won;t obstruct flow, as the outport will always be smaller than the T itself.

Like a 3/4-1/2-3/4 Tee
That means the outport must also be 1/2" for the piston to work.
Now you can use the more compact 1/2" elbow to connect the chamber..
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: maggotman » Sat Jul 04, 2009 6:44 am

i think the bes cheep powerfull valve is a burst disk or if you put a burst disk infront of the ball valve
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Unread postAuthor: inonickname » Sat Jul 04, 2009 7:04 am

Burst disks can get annoying. With my QEV rifle I'm building the only thing you need to carry is a shock pump and ammo. If I put a burst disk in then I need to carry a roll of alfoil, which will get scratched and cut in the bush, scissors, and then have to reload every single time I take a shot. For the increased noise, and only slightly better performance it just isn't worth it. Performance boost would be tiny seen as it's a 1/2" qev porting to a 5mm barrel at 400 psi.

BtB is correct, you could get a tee with the lower part reduced. The amount of porting you get is much lower than the tee size.
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Unread postAuthor: neeewwww » Sat Jul 04, 2009 8:50 pm

@BtB: Ahnn... I got the idea... And Shotguns are my favorite gun... Except for long range situations, of course ;x

@maggotman: I have to agree... and disagree... Yes, its cheaper and "easier" but not so practical...
Using a "homemade QEV", piston or anything else except burst disk... I just need to carry the cannon itself, shock pump and ammo...

* Looking for parts to build my own 1" QEV


o>
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Unread postAuthor: POLAND_SPUD » Sun Jul 05, 2009 1:58 am

@newww
I knew I coul build my own piston valve but the price of all the fittings needed to build one (and the difficulty of finding the right fittings) convinced me that buying a QEV is a better idea...
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Unread postAuthor: neeewwww » Sun Jul 05, 2009 4:50 pm

@POLAND_SPUD: I went to a hardware store today... To make a check-out list...
I easily found almost the whole list.. Except the damn spring --"
I dont know the name in english, but I found a fitting that I can exchange for the 1" hose barb (i just found 3/4" ones)...

http://www.cec.com.br/images/5/53686g.jpg
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Unread postAuthor: POLAND_SPUD » Sun Jul 05, 2009 6:56 pm

well I wasn''t that lucky.. but I think I'll build one as well... as I want to build something with larger valve

about that fitting in the pic... how can it be used instead of a hose barb ?I think you need a similar fitting to that one but with male threads

spings are not a problem.. they are everywhere
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Unread postAuthor: neeewwww » Mon Jul 06, 2009 9:10 am

Just screw the male screw of the fitting into the female screw on the Tee...

Not 3/4" Spring... x)
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