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Best type of QEV? (and pilot/fill valve)

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: rcman50166 » Mon Jun 09, 2008 4:59 pm

For the best QEV I would say the SQEV is the best. Here is a link showing how it works. http://www.humphrey-products.com/hpwpc.nsf/5D7E022D7C63F2338525732F00686AB0/$file/Super%20Quick%20Exhaust%20Valves.pdf It works like a coaxial piston pnumatic valve with vitually no leakage from chamber to pilot when vented.
Here's where you can buy. http://airinc.thomasnet.com/viewitems/specialty-valves-acc-/super-quick-exhaust-valves
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Unread postAuthor: potatoflinger » Mon Jun 09, 2008 5:32 pm

Hailfire753 wrote:I took a look at the fastenal 3/4 Alpha QEV, and it shows as .2 lbs, compared to the 2-3 pounds of a 3/4 diaphragm QEV. Is this accurate? Also, Is the alpha QEV the type where the shuttle is rigid or is it rubbery?

No, the Fastenal QEVs weigh more than .2 lbs, I believe that they are also in the 2-3 pound range.

I would test which type is better, but the diaphragm QEV I have is 1/4" and the Shuttle style QEVs are 3/4".

EDIT: I have two of the Alpha 3/4" QEVs and I would say that the shuttle is rigid, but around the edges it is a little bit rubbery. I can post a picture of it if you want me to.
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Unread postAuthor: Hailfire753 » Mon Jun 09, 2008 5:49 pm

Nah, I have seen pictures, I was just wondering if the shuttle material varied. Thats strange that the specs page is wrong though, thanks for your help.

Does anyone know if the shuttle/piston QEVs open faster than than the diaphragm QEVs?
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Unread postAuthor: al-xg » Tue Jun 10, 2008 4:24 am

It gets harder to open just because of higher O-ring friction at high pressures.

I have a 3/4' slide valve and just on its own with no pressure it wouls be hard to pull back 10times/s, at low pressures there isn't much difference but i've used it at 850psi (with a british 3/4" piston QEV) and the first time i used it, it didn't slide all the way back and there was some leaking.

I now use a 1/8" slide valve, wich is much easier to open, but there is still quite a diference in friction at high pressure.
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Unread postAuthor: POLAND_SPUD » Tue Jun 10, 2008 7:35 am

yeah I don't think that 10 shots per second are a needed here. 2/second would be fine
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Unread postAuthor: Hailfire753 » Tue Jun 10, 2008 7:51 am

Yeah, clide was getting around 2 per second, but that was at high psi. I would be using around 15-30 psi. Would that increase ROF at all?

My other option is using a modded QEV/blowgun type setup. ROF is a pretty big deal, used mainly for quick 3-5 shot bursts in woodsball. I assume I could actuate a 2 way valve with more speed?

I don't want to get into electronics, but are there any other 3-way options besides a slide valve?
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Unread postAuthor: POLAND_SPUD » Tue Jun 10, 2008 8:15 am

hmmm a spoolvalve ?
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Unread postAuthor: Hailfire753 » Tue Jun 10, 2008 8:37 am

Spoolvalve? Wow, before this I had never even heard/thought of that. Its like a backwards slide valve though, so it may run into the same problems.

Does anyone have any experience with them? A simplified 3-way sliding spool valve looks easy enough to build. A rotary spool looks more difficult, though.

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Unread postAuthor: al-xg » Tue Jun 10, 2008 8:58 am

You just need a 3/2 initialy open valve, should be quite easy to make.

Either you could make the whole thing and use O-rings, or you could moddify a ballvalve to work as a 3/2.

Another solution if you can bear to lose a tiny amout of extra air, is to just have the smallest possible pilot volume continuously filled by the chamber though a tiny hole (idealy a bearly opened valve so it can be ajusted) and then just have something like a blow gun to vent it.
You should be able to shoot quite fast with that as long as your chamber isn't to big.


I had homework to do, so i did these drawings instead :)

Image
Image
1- air goes in through a and to the QEV pilot port through b. When activated air from b is vented through c.
The part circled in red is optional at low pressures.
I didn't just put holes in the main pipe because when homemade they tend to destroy the O-rings.

2- Air enters through a, goes to QEV though c and is vented through b when the ball valve is turned and c lines up with d.
Sadly the space around the ball doesn't come filled up, when I tried this I had to pour epoxy inside the valve body.
If the body isn't filled air escapes as in the last drawing.

3- is already described above.

Voila
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Last edited by al-xg on Tue Jun 10, 2008 10:20 am, edited 1 time in total.
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Unread postAuthor: Hailfire753 » Tue Jun 10, 2008 9:29 am

Hailfire753 wrote:My other option is using a modded QEV/blowgun type setup.


Yeah, that is what I meant. I would rather not lose that performance, as I would have to mod the QEV by drilling a small hole in the shuttle and adding a return spring in it, slowing opening time slightly. Or... I could do your idea with a small valve directly to the chamber.

I don't think I would go with the ball valve, as I don't see any easy way to trigger it rapidly with one finger.

Hmm... I would rather go with the spool valve with pneumatic actuation (as in the above picture), but space is an issue on a portable gun, so I'll see what I can work out. Also, that setup is kind of overly complex - there would be 2 valves just to pilot and fill a QEV.

al-xg, do you think I will run into O-ring friction problems with the sliding spool valve, like on the slide valve? I would probably use a neoprene/washer sandwich to make the three piston seals.

Also, would the ROF of a spool valve be faster than a slide valve, both manual actuation?
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Unread postAuthor: Carlman » Tue Jun 10, 2008 9:49 am

rcman50166 wrote:For the best QEV I would say the SQEV is the best. Here is a link showing how it works. http://www.humphrey-products.com/hpwpc.nsf/5D7E022D7C63F2338525732F00686AB0/$file/Super%20Quick%20Exhaust%20Valves.pdf It works like a coaxial piston pnumatic valve with vitually no leakage from chamber to pilot when vented.
Here's where you can buy. http://airinc.thomasnet.com/viewitems/specialty-valves-acc-/super-quick-exhaust-valves


im getting 6 from america for 20$ plus shipping :D i think they are 1/2"
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Unread postAuthor: Hailfire753 » Tue Jun 10, 2008 10:01 am

20$ aussie or 20$ USD? 1/2" QEVs from that site show up as $ 32.80 USD, so you got a great deal, probably somewhere else though.
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Unread postAuthor: Carlman » Tue Jun 10, 2008 10:12 am

Hailfire753 wrote:20$ aussie or 20$ USD? 1/2" QEVs from that site show up as $ 32.80 USD, so you got a great deal, probably somewhere else though.


$19.80 aussie off ebay for 6 :shock: :shock: lol
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Unread postAuthor: al-xg » Tue Jun 10, 2008 10:26 am

whoops I edited a bit late, err, there are also friction problems with the spool valve, but a blowgun type trigger can be added to provide leverage and it will probably be fine.
The spool valve should be easier to open, so would make the ROF easier to achieve.
But do people with mechanical single triger paintball guns even achieve 10bps?

Oh and no real need to mod the QEV, just screw in a small T, and reduce pilot volume as much a possible without affecting flow.
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Unread postAuthor: Hailfire753 » Tue Jun 10, 2008 12:33 pm

Wow, nice pics al-xg.

A ROF of 7-9 bps is about average for a semi-auto with no mods or pneumatic assistance. I can pull a light-resistance trigger about 7-8 times a second (mime pulling a trigger while timing yourself). However, some markers have "walkable" triggers - ones that are so easy to actuate you can alternate tapping two fingers against the trigger to get about 14 bps. I would like 10 bps for a response trigger, but around 7 bps is acceptable for manual.

I had planned to add a trigger to the slide valve, similar to clide's slider. I am surprised he only got about 2 bps with that setup.
Image

I will either go with the QEV/Tee/blowgun or the QEV/spool valve.

I understand your pictures 2 and 3, but in 1 wouldn't air escape through port "C" while filling?

I will draw up some pictures of my own soon, to show how they fit into my design.
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