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Pneumatic QEVs on eBay.

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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Pneumatic QEVs on eBay.

Unread postAuthor: r00kie » Tue Oct 12, 2010 6:30 am

G'day, I should probably also introduce myself here, I've been lurking for a few years now and learned a lot off this forum, I'd like to extend a big thanks to contributing users and staff for the vast amount of information I've pulled off here, I've definitely learned a lot.

I've been looking at QEVs on eBay, I've found some interesting valves that look quite compact and aesthetic that I'd like to use.

Here's an example of what I mean.

Has anyone tried using these in a launcher? From what I understand it would work in the same manner as a modified solenoid valve (pilot area released causing the exhaust port to open).

I'm not sure if the actuating speed would be as fast or if it even does what it appears to, but it definitely looks better than a modified solenoid, it's also smaller (there are varying sizes, the one I linked was 1/2", they seem to go all the way down to 1/8").


Thanks,
Paul.
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Re: Pneumatic QEVs on eBay.

Unread postAuthor: jackssmirkingrevenge » Tue Oct 12, 2010 6:43 am

r00kie wrote:Has anyone tried using these in a launcher? From what I understand it would work in the same manner as a modified solenoid valve (pilot area released causing the exhaust port to open).


That's correct, they are generally faster and better than modded sprinklers and can also be taken to higher pressures.

The type you linked to is very popular on the forum, here's a classic example but there are many more in the pneumatic cannon showcase if you have a browse there.

With a pop-off pilot, you can even make it go full auto ;)
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Re: Pneumatic QEVs on eBay.

Unread postAuthor: r00kie » Tue Oct 12, 2010 6:55 am

jackssmirkingrevenge wrote:That's correct, they are generally faster and better than modded sprinklers and can also be taken to higher pressures.

The type you linked to is very popular on the forum, here's a classic example but there are many more in the pneumatic cannon showcase if you have a browse there.

With a pop-off pilot, you can even make it go full auto ;)


Thanks JSR, that's a relief. Sounds like a nice easy way to get a QEV, I've attempted to make my own piston valve but had some leakage problems that I'm still trying to iron out.

I love your work by the way, your launchers look really nice, I've bumped into a few while lurking. :)
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Re: Pneumatic QEVs on eBay.

Unread postAuthor: jackssmirkingrevenge » Tue Oct 12, 2010 6:59 am

r00kie wrote:I've attempted to make my own piston valve but had some leakage problems that I'm still trying to iron out.


Don't be shy to post it here if you need help, heaven knows that if I didn't post my failures as well as my successes there wouldn't be a lot of my launchers on this forum ;)
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Unread postAuthor: lozz08 » Tue Oct 12, 2010 7:09 am

Welcome to the forum; got a particular launcher in mind?
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Re: Pneumatic QEVs on eBay.

Unread postAuthor: r00kie » Tue Oct 12, 2010 7:11 am

jackssmirkingrevenge wrote:Don't be shy to post it here if you need help, heaven knows that if I didn't post my failures as well as my successes there wouldn't be a lot of my launchers on this forum ;)


I feel that I should try to work everything out myself before asking for help, as there really is a lot of information on here for troubleshooting already. I think part of the problem is the sealing face being a bit too sharp and the rubber on the washer being tough, the hardest part is getting it to align perfectly when the piston is closed, but I think I'm making process.

I need to get some more epoxy as well, I've found that hot glue pistons are not very reliable, they tend to expand a bit in the heat, especially on hot Australian days. :?

If it ends up doing my head in, I'll post some pictures up and try and get some expert advice. :P

lozz08 wrote:Welcome to the forum; got a particular launcher in mind?


Thanks, I'm going for smaller bore with the QEV I mentioned, I'd like to get a sleek rifle set up with a crafted stock (which is one of the reasons I was after something smaller than a solenoid valve), but I'd also like to try out something larger that launches tennis balls (my dog would love me forever). :)
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Unread postAuthor: Guaps » Fri Oct 15, 2010 7:02 pm

So can you use that ebay QEV to replace this brass valve in the how to section?
http://www.spudfiles.com/forums/self-closing-piston-valve-brass-fittings-t17609.html

I'm trying to build the gun in the video below, but I can't find the hose barb anywhere around here (or on the internet for that matter)
http://www.youtube.com/watch?v=2bvXiswEDSo&feature=related
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Unread postAuthor: Crna Legija » Fri Oct 15, 2010 8:40 pm

yes a QEV is just a factory made piston valve you connect it the same way you would with the one MRR made a how to about.
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Unread postAuthor: r00kie » Fri Oct 15, 2010 10:23 pm

Guaps wrote:I'm trying to build the gun in the video below, but I can't find the hose barb anywhere around here (or on the internet for that matter)
http://www.youtube.com/watch?v=2bvXiswEDSo&feature=related


I had the same problem when I was building a piston valve. I'm not sure where you're from, but I eventually managed to find something similar in the irrigation section of Bunnings.
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Unread postAuthor: Guaps » Mon Oct 18, 2010 11:44 am

I'm in the States - no Burnnings around. Thanks though.
I found a hose barb in the irrigation section at Home Depot, but as others have said, the threads were much coarser and will not work. It would be a lot more fun to make my own QEV, but I think this ebay item is my only option for now.
Thanks for the help!
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Unread postAuthor: r00kie » Mon Oct 18, 2010 6:25 pm

I've ordered my QEV from eBay, it's on it's way. :)

I know this is straying off my original topic a bit, but I'm having some trouble with the "gun optimiser" in GGDT.

I've been using it to get a good C/B ratio and muzzle velocity before going out and buying some copper, but I'm getting "division by zero" crashes when I try to use a fixed barrel length. Has anyone else experienced this?
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Unread postAuthor: Ragnarok » Mon Oct 18, 2010 6:36 pm

r00kie wrote:Has anyone else experienced this?

Yes, it's a common error.
My advice: Don't bother. What GGDT means when it says "optimal" is only that way from a certain point of view.

It means that wasted energy is minimised. However, it's like fuel consumption in cars - a fuel efficient car is usually also a pretty slow car.
Similarly, an efficient launcher usually doesn't have much guts. Most of us are prepared to sacrifice some efficiency for the sake of a power increase - I'd recommend you do the same - just choose a chamber size that you're prepared to put up with.
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Unread postAuthor: r00kie » Mon Oct 18, 2010 7:29 pm

Ragnarok wrote:
r00kie wrote:Has anyone else experienced this?

Yes, it's a common error.
My advice: Don't bother. What GGDT means when it says "optimal" is only that way from a certain point of view.

It means that wasted energy is minimised. However, it's like fuel consumption in cars - a fuel efficient car is usually also a pretty slow car.
Similarly, an efficient launcher usually doesn't have much guts. Most of us are prepared to sacrifice some efficiency for the sake of a power increase - I'd recommend you do the same - just choose a chamber size that you're prepared to put up with.


I see, thanks Ragnarok, I hadn't thought of it that way.

I noticed that it tries to calculate it so at the time the projectile leaves the barrel the chamber has dumped all it's pressure. I understand that more air will give you more power, but at diminishing efficiency. I might go for a 50-70% drop at the time the projectile leaves the barrel.

Playing a bit manually, I managed to get a 70% drop with 108ft/s velocity (1/2" barrel, 200psi). I'm not sure how efficient that is, as I don't use imperial day-to-day, and I've never had to deal with muzzle velocity before.

I'll play a bit more and see what I can get. :)
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 19, 2010 4:22 am

r00kie wrote:108ft/s velocity (1/2" barrel, 200psi)


Unless your projectile weighs a ton, that's not a very impressive value for muzzle velocity. A typical "adult" air rifle will push a 1 gram lead pellet to 500-600 fps.

Care to post a screen cap of your GGDT model?
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Unread postAuthor: r00kie » Tue Oct 19, 2010 5:09 am

By changing the projectile mass to one gram, it flew up to 245ft/s. I had it set at an embarassing amount that I won't mention. :p

By fixing a few more (embarrasingly set) options, I got it up to 674 ft/s, which makes me think I'm doing well after your post JSR.

Here's a screenshot anyway, in case you still want to take a look, I'm sure you'll find something to correct me on. :oops:

Image
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