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Educate Me: Why wouldn't you use a QEV?

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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Educate Me: Why wouldn't you use a QEV?

Unread postAuthor: tauschung » Tue Feb 02, 2010 2:57 pm

I've been looking through old posts, and noticed that most of the launchers can be lumped into one of these categories: ball valve, sprinkler valve, diagphragm valve, piston valve, and quick exhaust valves. (I'm not sure if burst disks count as a valve?)

I realize that QEVs are more expensive. But, if you take that factor away what other reasons are there? QEVs are optimized the moment you get them..and it does not seem to be hard to get them to go full auto.

Is it because some people enjoy the project..and building their cannons from the ground up? Or is it due to the size of your project?
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Unread postAuthor: hi » Tue Feb 02, 2010 3:04 pm

the only three reasons i can think of are A) you cant afford one or B) you enjoy a good do it your self project and want to make a piston valve/diaphragm valve., or C) you have some other valve laying around.
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Unread postAuthor: D_Hall » Tue Feb 02, 2010 3:24 pm

Honestly, the ONLY reason to use a modified sprinkler valve is if you want to have that "do it yourself" feeling. Small QEVs with similar performance are not significantly more expensive than sprinkler valves (plus fittings). Add to that the fact that the QEV is optimized for the job and much more robust... And there just is no economic or performance based reason to go with sprinkler valves.
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Unread postAuthor: mega_swordman » Tue Feb 02, 2010 3:50 pm

Availability would be why in my case. I can go to any hardware store and by a 1" Sprinkler Valve whereas the only practical QEV I can find would need to be shipped from the UK.
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Unread postAuthor: iknowmy3tables » Tue Feb 02, 2010 5:42 pm

I agree availability, In my case I still don't have a credit card to buy stuff online, and I don't feel like paying/asking others to use theirs. I built the deus ex machina from just from hardware store parts, although the fill rates through a moded 3way blowgun and sprinkler valve is quite pathetic

also when you scale up larger sizes over 3/4" prices get ridiculous, really large sch 40 fittings are bad enough,
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Re: Educate Me: Why wouldn't you use a QEV?

Unread postAuthor: Ragnarok » Tue Feb 02, 2010 9:27 pm

tauschung wrote:I've been looking through old posts, and noticed that most of the launchers can be lumped into one of these categories: ball valve, sprinkler valve, diagphragm valve, piston valve, and quick exhaust valves. (I'm not sure if burst disks count as a valve?)

Okay, reasons why anyone might use each one of those:
Ball valve - simplicity and availability
Sprinkler valve - availability
Diaphragm valve - customisation
Piston Valve - customisation
QEV - ready made package
Burst disk - raw performance

QEVs are good, no doubt about it, but a piston valve has the advantage of being built to whatever specs you like, where a QEV only comes in very specific sizes. A QEV may be naturally impressive, but if you're really talking about a truly optimised valve, piston valves may take more work, but they can be a lot better in the long run.

Also, piston valves really do perform better.
Take the main valve and pilot valve on HEAL - each has about the same external dimensions as the other (while the piston valve is slightly longer, it's also narrower).
But in terms of performance, the piston valve makes absolute mincemeat of the QEV - it has around three times the flow, and opens just as fast. If that doesn't illustrate why I'm using a piston valve for that job, nothing ever will.

Actually, to continue on that note, it depends entirely on what you want the valve for. As a main valve, that's one thing, but if you're not looking for a main valve...
To give an example, the reason why there's a ball valve in that picture is because it's a strictly manual valve with very high flow when fully open.
If that valve is shut, the cannon will not fire. If it's open, its effect on the performance of the cannon is so minimal as to be inconsequential.
In other words, there's no better safety.
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Unread postAuthor: tghhs » Tue Feb 02, 2010 9:33 pm

Well....

This totaly depends on bore. For a small one a QEV is great if you can get it

When you start to make bigger bores, the off the shelf solution aren't feasible, simply a piston or dump valve is far more efficient and cheaper than anything bought.
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Unread postAuthor: shadowzzz » Tue Feb 02, 2010 10:24 pm

And some people prefer co-axial launcher to over-under configurations, and you can't use a QEV in a co-axial config, right? (except maybe as pilot).
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Unread postAuthor: Hubb » Wed Feb 03, 2010 1:12 am

Availability here, too. I can't find it anywhere locally.
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Unread postAuthor: jeepkahn » Wed Feb 03, 2010 4:16 am

Hubb wrote:Availability here, too. I can't find it anywhere locally.


Dude, I'm sure theres a Fastenal within 20 miles of you, there almost like starbucks these days, one on every corner...
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Unread postAuthor: Hubb » Wed Feb 03, 2010 4:33 am

jeepkahn wrote:
Hubb wrote:Availability here, too. I can't find it anywhere locally.


Dude, I'm sure theres a Fastenal within 20 miles of you, there almost like starbucks these days, one on every corner...
Yes, you are right. There is one right in the middle of town - without QEV valves :cry:
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Unread postAuthor: jeepkahn » Wed Feb 03, 2010 5:06 am

Have you asked them to get them for you??? coming out of Indy they'd have them in 2 days... Mine started stocking them at my request, they keep 3 of each size on the shelf for whenever I need them... :D

And typically you don't have to prepay, just tell them what you need and then pay when you pick them up... And normally if you tell them what they're for, they get into it and will throw in discounts...

my local fastenal actually set-up an in house account for me, as "airgun dude"...
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Unread postAuthor: Hubb » Wed Feb 03, 2010 1:38 pm

I haven't asked, but I know now that I can. Thanks.
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Unread postAuthor: Brian the brain » Wed Feb 03, 2010 2:21 pm

I use whatever gets the job done.
I modify QEV's to my need, make them chambersealing or able to fill from the chamber side.

I like them because they are compact.That's it.
They can be customised.

I've made several larger piston valves, but sometimes big is not what I need.
When I do ( big cannon) there is no substitute to piston valves IMO.
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Unread postAuthor: boyntonstu » Wed Feb 03, 2010 2:45 pm

A 3/4" wood dowel 36" long from HD/Lowes can be used to make 15 pistons for less than a few bucks.

10 'O' rings for 2 bucks and you are in bizniz.

That is what is inside this:

Shooting the Trom-Boyn pneumatic nail dart rifle at 200 psi

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

It has gone to 550 psi without any problem.
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