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

Unread postAuthor: neeewwww » Wed Jul 01, 2009 10:11 am

Hi there guys...

Since I saw some "Spray and Pray" cannons at YouTube... After that
I got the airgun disease... So I took some google research and arrived here...

I spent a lot of time looking at Pneumatic Showcase... and decided to use Brass or copper, because here in Brazil, I guess we don´t have "high pressure rated" PVC pipes...

Then I decided to go Ball Valve actuated by a spring. Sprinkler Valve are very expensive here, due lack of use (I guess), Piston I´m not really confident that I can build one in my first airgun...
So, I started buying stuff, fittings and etc. I spent 30BRL (Brazilian Reais), almost 15USD, just in:

2 - 1" Brass/Copper Tee
2 - 1" Brass/Copper End Cap
1 - 3/4" Brass/Copper 90º
1 - 3/4" Brass/Copper End Cap

None has screws, all needs soldering.

So I realize "I´m spending more money that I expected on this thing... And I will use Ballvalve... I guess I will get really dissapointed ¬¬""

Then, I was looking for some QEV Cannons, and its like 90% better than a ballvalve actuated by a spring.

Now the question is:

I just found 1/2" QEV (rated 12bar or 175psi), but I wanted a 3/4"...
Will 1/2" QEV act "like" a 3/4" QEV or the difference will be enourmous?

The cannon specs/layout will be like the BTW Sawed-off Mark II

Except:
Chamber will be: 1" x 20"
Barrel: 1" x 15" and 3/4" x 15"
Filling method: Hand Pump
Pilot Valve: 1/2" or 3/4" ballvalve.

Now guys, 1/2" QEV will be enought?


Thanks
Sorry bout my english x)


o/
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Unread postAuthor: POLAND_SPUD » Wed Jul 01, 2009 10:45 am

welcome to spudfiles!

first of all, I suggest you to switch to threaded malleable iron fittings and pipes (also known as 'galvanized fittings and pipes') here is a picture of them -> picture


they are good becasue you don't need to buy new parts every time you build a new gun... you can start with a lenght of pipe for the chamber and the barrel a QEV, ballvalve and a quick connect fitting (for filling)...

then you can recycle your parts to build something new, try different barrel and chamber sizes etc.

after a few months you'll have a large collection of pipes and fittings... I rarely buy parts now.. I already have them


well my story is similar to yours as far as material availability in my country is concerned...
when I was a beginner I also noticed that QEVs are parts that offer good power and generally make things easier (you don't have to build a piston valve you just buy it)

I bought a 1/2" QEV but I think it wasn't the right choice... 1/2" offers optimal flow for 10mm barrel or smaller...

a 3/4" version is not much more expensive but it offers more power for marble sized barrels (~16 mm) and larger

EDIT
ohh one more thing, you might consider building a fridge compressor (it's a high pressure pump theat you can build from a compressors that are in every fridge
here is my thread about them -> http://www.spudfiles.com/forums/t-t11866.html it's an old text but it should give you an idea of what it is and how to build one (it's really easy)

they are really great for guns built from malleable iron fitings and QEVs as they genreate higher pressures than normal compressors, which means MORE POWER :)
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Last edited by POLAND_SPUD on Wed Jul 01, 2009 10:58 am, edited 2 times in total.
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Unread postAuthor: Ragnarok » Wed Jul 01, 2009 10:51 am

There will be something of a difference. The 3/4" QEV will provide more power.

My estimation is anywhere from 20-50% more muzzle energy, depending on the barrel, projectile and pressure.
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Unread postAuthor: neeewwww » Wed Jul 01, 2009 11:35 am

@POLAND_SPUD - Thanks for reply... I just realized that threaded fittings and pipes are better than "solder ones" before I bought it...

But I will continue using them for my chamber. I guess the chamber is the one part that doesnt requires much maintence... So it will be: 1" Cap -> 1" Coopper ou Galvanized Pipe -> 1" Tee -> And then a threaded adapter...
I thought too about a fridge compressor, I will look for one... But, I guess I can pump at 10bar using a regular shock pump? Didnt I?

@Ragnarok - Thanks x) - First... Good, beautiful, amazing job at HEAL ^^
Second, I thought that a 3/4" QEV would be better than a 1/2", but just 6mm difference from each other will performe like 20 ~ 50% o.O


So... I guess I will need a 3/4" - Anyone knows any store that exports to Brazil? BCarms offline... Any suggestions?
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Unread postAuthor: POLAND_SPUD » Wed Jul 01, 2009 11:57 am

well a shock pump should be able to reach 10 bar with no problems but it has small flow

copper is useful for barrels (as they have to be smooth inside) but not for chambers... well that's just my suggestion - it might work for you fine

but from my experience... copper = troubles
even as simple part as a threaded adapter casue me troubles
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Unread postAuthor: neeewwww » Wed Jul 01, 2009 12:12 pm

@POLAND_SPUD - Small flow = more time to fill. Or can I have some troubles with QEV? I don´t know much about them (QEV), they need some minimal pressure to fill the chamber, and some minimal pressure to actuate?

Copper - 28mm 2.5m costs about 65BRL or 33USD. I guess soldering copper is not THAT difficult... Just some Flux, soldering iron and jet torch...
And I will use exaclty 2.0m in my whole gun...

If I buy Brass or galvanized pipes... The minimal sell lenght is about 6m (I dont know the price). Otherwise I cant take a look at junkyards...
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Unread postAuthor: POLAND_SPUD » Wed Jul 01, 2009 12:19 pm

I guess soldering copper is not THAT difficult... Just some Flux, soldering iron and jet torch...
lol that's the point I thought that's simple too (it turned out it isn't... or I did something in the wrong way) :D


Copper - 28mm 2.5m costs about 65BRL or 33USD
I suspect that's more than for an iron pipe

QEVs shouldn't have any problems with small flow... I meant that small flow wastes your time... and remember that you have to pump it yourself (or use your younger brother/sister to do it)
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Unread postAuthor: neeewwww » Wed Jul 01, 2009 12:30 pm

@POLAND_SPUD - Lol... I saw several videos at Instructables and YouTube... It seems to be SO easy to do... 4 Steps:
1 - Clear the fittings
2 - Apply Flux
3 - Apply jet torch
4 - Apply soldering iron... And done!

Seriously... Poland_Spud... You get me down/sad --"

All right... My project got a delay... First I need to find a 3/4" QEV, and then I look for fittings, pipes and whatever...
I found a 22mm (3/4") 2.5m - Grade E - Cooper Pipe... Maybe, it will be my choice... 23USD

Thanks for the help POLAND_SPUD and Ragnarok...

Now... I need a 3/4" QEV - Anyone can send-me one? I obviously pay x)

o/
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Unread postAuthor: Technician1002 » Wed Jul 01, 2009 12:52 pm

neeewwww wrote:@POLAND_SPUD - Lol... I saw several videos at Instructables and YouTube... It seems to be SO easy to do... 4 Steps:
1 - Clear the fittings
2 - Apply Flux
3 - Apply jet torch
4 - Apply soldering iron... And done!

Seriously... Poland_Spud... You get me down/sad --"

All right... My project got a delay... First I need to find a 3/4" QEV, and then I look for fittings, pipes and whatever...
I found a 22mm (3/4") 2.5m - Grade E - Cooper Pipe... Maybe, it will be my choice... 23USD

Thanks for the help POLAND_SPUD and Ragnarok...
o/


The pros make it look easy. :D In practice going from not enough heat to too much heat (burnt flux) leaves only a relatively small temperature range where the solder flows properly all the way into a joint. Done wrong, it always leaves a path for a leak. With some practice, good soldering joints can be made. A soldering iron is NOT used to solder copper pipe. Just the torch, flux, and solder. Pick up a couple extra parts to practice on. A half inch pipe and a dozen couplers makes good practice material. Look for the solder to wick into the joint all the way to the bottom and all the way around the pipe.

(I do both some plumbing and high pressure heat pump hard silver brazing of copper pipe.)
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Unread postAuthor: neeewwww » Wed Jul 01, 2009 1:37 pm

I was looking for some QEV specs.
Here is one from Parker:

Urethane Diaphragms
1/2" - Flow (SCMF): 450
3/4" - Flow (SCMF): 550

* I dont know what SCMF means...

Nitrile and Fluorocarbon has the same difference 1/2" Y and 3/4 Y + 100.
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Unread postAuthor: Ragnarok » Wed Jul 01, 2009 2:45 pm

POLAND_SPUD wrote:copper is useful for barrels (as they have to be smooth inside) but not for chambers... well that's just my suggestion - it might work for you fine

I have to disagree. Smooth chamber walls can really help performance at the high end of things. It's no coincidence that I'm eliminating every single hard edge in my high power designs these days.

Also, I've never found copper soldering hard. It might not always be neat, but getting a secure join doesn't demand much in the way of skill.
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Unread postAuthor: neeewwww » Wed Jul 01, 2009 2:57 pm

Woah! What a f*cking HUGE difference between 1/2" and 3/4", talking about money! Holy crap!

1/2" QEV - 51BRL or 26USD
3/4" QEV - 140BRL or 72USD

¬¬"

And LaunchPotatoes.com asking for 31USD for a 3/4" or 62USD for 3/4" QEV + Hose + Blow Gun + Quick Disconnect...

Better go for a single 3/4" or better ask "complete set"?
And, any comments about LaunchPotatoes?

o>
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Unread postAuthor: spudmanb3 » Wed Jul 01, 2009 3:09 pm

If you were originally planning to use a ball valve then a 1/2" qev should be enough. I would look at the price of a 3/4" qev and if it's only a few dollars more buy it.
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Unread postAuthor: neeewwww » Wed Jul 01, 2009 3:16 pm

@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?

Here in Brazil, its a little difficult to find QEV and much more to find a Sprikler Valve...

Here a 1/2" QEV costs about 50BRL and a 3/4" about 150BRL. I guess the difference dont worth my money (here)... If I choose importing it from LaunchPotatoes, it will be cheaper... very cheaper... I buy a 3/4" for the "same" price I buy a 1/2" here.

LaunchPotatoes asking for 31USD. But they need to export, and I dont know the final price (tax, shipping and whatelse).
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Unread postAuthor: POLAND_SPUD » Wed Jul 01, 2009 6:34 pm

you need a torch to solder... ohh well maybe I am just soldering challenged or something but I can't do it right... for me threaded fittings are the way to go... I guess that's a matter of personal preference and prices

from my perspecitve switching the chamber to a larger one takes about 15 seconds max (you can use o rings to avoid using PTFE tape)... it's hard to beat that with

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

@neeewwww
1/2" QEV - 51BRL or 26USD
3/4" QEV - 140BRL or 72USD
hmmm that's weird.. a 3/4" version is about 25 - 30% more expensive than 1/2" (at least here in poland)
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