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

Unread postAuthor: Hailfire753 » Sun Jun 08, 2008 9:00 pm

It's summer, and I would like to start making a paintball gun as soon as I can convince my dad.

The gun will use a QEV/ homemade sleeve valve combo to achieve semi/auto fire. I plan to use a 3/4 QEV, but I need it as small, fast, lightweight, and cheap as possible, and with a high flow. I would like it to be able to tolerate high-as-possible pressures, but this is for off-field target carnage (around 20 psi on field, up to CO2 pressure off-field.)

From what I understand, there are two factors affecting valve performance: opening time and Cv, or flow coefficient. There are several types and brands of QEVs I have seen, some using diaphragms, others using shuttles.

Question 1: Do shuttle QEVs open faster than diaphragm QEVs?
Question 2: Are diaphragm QEVs able to handle 150+ psi past their rating like shuttle QEVs?

This site shows what appears to be a 3/4" shuttle QEV with a CV of 4.08. This site (.pdf warning) shows a 3/4 diaphragm QEV with a CV of 10.55. I am leaning toward the diaphragm, but it appears to be bigger and heavier than the shuttle. Prices are not listed. Also, different companies use different ways to measure CV, but it is generally calculated as the number of gallons of water that can flow through the valve at 100 psi with a 10 psi drop in pressure per minute.

Question 3: What kind of performance difference would I see between the two?

For paintball, I need EXTREME fill speed (Cv), a cycle rate of around 10 per second, and little pilot air.

Also, I would be grateful for any suggestions for alternative QEVs or a completely different valve setup.

Shuttle QEV
Image

Diaphragm QEV
Image
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Last edited by Hailfire753 on Tue Jun 10, 2008 9:32 am, edited 1 time in total.
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Unread postAuthor: POLAND_SPUD » Sun Jun 08, 2008 9:16 pm

The gun will use a QEV/ homemade sleeve valve

good combination - AFAIK ragnarok used it.. I am planning to do the same

I suppose that the Shuttle QEV is beter... it seems more sturdy.. perdonaly I use the shuttle QEV and it works fine to 450 - 500 psi

most europeans use Shuttle QEV
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Unread postAuthor: Hotwired » Sun Jun 08, 2008 10:03 pm

Shuttle eh? I've always called them piston types.

As you can see from this diagram, both types have a moving part, the diaphragm is not clamped but is free to flex its edges to allow air past in filling and its centre to allow for exhausting.

Image

Anyway the primary advantage of the "shuttle" type is the fact that they don't have the great protruding flanges of the diaphragm type.

I have seen that diaphragm types appear to have greater flow than shuttle types but I didn't think it was more than double. Oddly enough I'm certain I've also read that shuttles are designed to provide greater flow than "normal" diaphragm types.

I'll look about.

The smallest QEV you're comfortable with will keep the pilot volume down and a slide valve screwed right into the fill point will give absolute minimum pilot volume.

The ROF is actually more likely to depend on the slide valves flow than the QEV's as you really will not want to be operating a 3/4" slide valve with a finger at any high rate. In fact no paintball guns operate the main valves directly, usually using fiddly pneumatics to keep the trigger pull down if they're not electric.

I can't see 10bps with a physically operated pilot valve really.
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Unread postAuthor: Hailfire753 » Sun Jun 08, 2008 10:40 pm

Hmm, thanks for the advice. I thought the piston/shuttle QEV to be the more sturdy of the two, and I also heard that those flanges of the diaphragm limit flow. Another site showed the diaphragm at around 7 Cv. Could be a different make, or a different Cv testing method.

Why would I "not want" to operate a 3/4 slide valve quickly? Would the pilot air be annoying/painful? Or would my finger get tired? I don't think it will be an issue, as it is not hard to slide lubed pipe back and forth with no air pressure resistance (I think?). Also, there will be pneumatic assistance in that department.

See the animation, or this.
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Responce Trigger animation.swf [ 17.39 KiB | Viewed 2381 times ]

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Unread postAuthor: Carlman » Sun Jun 08, 2008 11:27 pm

wel i have fired my 1/4" diagpragm qev manytimes at 300psi pressures
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Unread postAuthor: MrCrowley » Sun Jun 08, 2008 11:29 pm

And i've fired my American style Detrol QEV ('phragm) at 300psi many times as well.

Apparently they don't start leaking until about 750 PSI+.
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Unread postAuthor: potatoflinger » Mon Jun 09, 2008 9:13 am

I have a diaphragm QEV and two shuttle QEVs and I prefer the shuttle QEVs because they fit into a design better (they don't stick out around the sides) but I never bothered to look up which type has better flow.
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Unread postAuthor: SpudFarm » Mon Jun 09, 2008 9:28 am

i bougth a diaphragm QEV to look at it, and i hokked it up to a small chamber and it has quite abit of flow.

pistons beat diaphragm in flow.
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Unread postAuthor: Hailfire753 » Mon Jun 09, 2008 12:31 pm

Hmm... 750 psi? Crazy! I might have to go with a diaphragm just because of that.

QEVs seem pretty hot-swapable, does anyone with both types want to test the performance difference?

Also, a simplified version of the piston valve in clide's slider is an option

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Unread postAuthor: Hailfire753 » Mon Jun 09, 2008 1:47 pm

Edit: whoops, double post. accidentally clicked quote instead of edit.

BTW, does anyone have a link to where I could buy an "American style Detrol QEV" or a specs page?
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Unread postAuthor: al-xg » Mon Jun 09, 2008 2:02 pm

You will have a tough time pulling a 3/4" slide valve back at CO2 pressures, they even tend to get stuck half way if not pressed hard enough and can leak.

Even with the response trigger system i can't imagine you would ever get 10bps, even with no pressure at all, it would be hard to open a sleeve valve that fast.
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Unread postAuthor: MrCrowley » Mon Jun 09, 2008 2:14 pm

Hailfire753 wrote:Hmm... 750 psi? Crazy! I might have to go with a diaphragm just because of that.

I'm positive the British piston ones can take that also. I was just saying that it's not only the British one that can take high pressures.

Also you can get the American Detrol's on McMaster.
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Unread postAuthor: frocksie » Mon Jun 09, 2008 2:33 pm

I would suggest Fastenal, I'm not sure if they carry Deltrol valves, but I bought a 3/4" QEV from Alpha Technologies, and it is great.

Fastenal QEV Page.
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Unread postAuthor: POLAND_SPUD » Mon Jun 09, 2008 3:10 pm

al-xg could you say more about slide valves ? I haven o personal experience with them.. are they like QC fittings ? (that is they are harder to open when used at high pressures ?)
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Unread postAuthor: Hailfire753 » Mon Jun 09, 2008 4:05 pm

I completely forgot about McMaster QEVs, I thought that they were pistons. They show a Cv of 7.84. Thanks MrCrowley.

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?

As for slide valves, I don't see where or why it would get stuck. Pressure is equalized in both directions, so as far as I know it would not be more difficult to open with more pressure. But then again, I don't have any personal experience either, just common sense physics (could be wrong).
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