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QEV and building up

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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QEV and building up

Unread postAuthor: KnooBill » Fri Sep 16, 2016 12:24 pm

Hello, I'd like to build a pneumatic gun. It will be single shot, a strong bike pump and perhaps a PCP pump later on. As I do not have access to many tools as others on here, by researching I found that a QEV would work best as my main valve. Going by projectile measurements, I'll be using a 3/8'' port. Then I looked for the best available commercial QEV, ended up with Humphrey. Sadly I can't get it here in EU, is anyone familiar with Norgren quick exhaust valves? They look similar.
Specifications
http://cdn.norgren.com/pdf/en_5_10_410_T70.pdf
What I don't understand is that the mechanism is "poppet valve". I am not sure whether it will work for my purposes.
I'll take any other suggestions on better QEVs and appropriate pilot valves plus triggering. Money isn't much of an issue, availability UK/EU is.
The bike pump has 220 psi rating.
The barrrel will be the main metric for the gun's size. 3/8'' diameter, 12'' length (approximate, doing the closet to inches from cm) Chamber is 1.33 times the barrel's volume, 1/2'' diameter, 10' length. I am unsure if this is optimal, however it is close to some other designs on here.
I played around on GGDT but I got weird graphs, perhaps because I had to improvise on some valve measurements.
Thank you.
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Re: QEV and building up

Unread postAuthor: Doodmens » Fri Sep 16, 2016 3:22 pm

I do not have experience with the norgren valves, but I can say that a cheap Chinese valve will work just fine! I have started using those and I still do because 1) they are very simple 2) easy to mod 3) very cheap (although you said money isn't the issue).

http://www.ebay.com/itm/Black-Pneumatic-Quick-Air-Exhaust-Valve-3-8-Inlet-Ports-Aluminum-Alloy-QE-03-/161996489490?hash=item25b7be4312:g:kiEAAOSwdzVXkyPy

Have you chosen a pilot valve yet?
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Re: QEV and building up

Unread postAuthor: Ianbuckwell » Sat Sep 17, 2016 10:30 am

What country are you in? I managed to source Humphries QEVs in the UK. Check their website as iirc it lists distributors in various countries. As said above I am sure you wont have any problems with a Chinese one from ebay and if you do they are cheap to repair/replace. I used one of these QEVs and unintentionally it held 350-400psi without problem and also offers fast opening and great flow, I used a 3/4" for a 12mm barrel, only problem if looks is a problem they are kind of larger diameter housing.

You may wish to try longer barrels/larger chamber for improved performance especially if using bike pump pressure. For the valve Humphries make some lovely 3way valves perfect for piloting QEV, one I looked at was something like mjv3 (or mjv3o, sorry cant remember) otherwise a slide valve is a good option which are available from China cheaply otherwise Norgren make a nice one.

In UK biggest problem I found was barrel/ammo diameter, some companies use metric others imperial and although the outer diameter is listed and wall thickness it nevers seems to give the exact internal diameter. For acurate strong tube you may want to look at a hydraulic suppliers rather than ebay. I used this company simply because it was fairly close to me

http://hyphose.com
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Re: QEV and building up

Unread postAuthor: KnooBill » Sun Sep 18, 2016 6:20 pm

Thanks for the responses! I was looking at a tee with schrader valve and blowgun/ball valve, but 3 way valves entice me. I cannot fully understand them. Many thanks Ian for letting me know about UK distributors, I messaged both and awaiting for a quote. I can have parcels forwarded to me from the UK curently.
Could you explain about the 3 way valves and which model I could utilize? Performance is the prime criterion. Similarly, should I notice no better performance at my rather low pressures with the humphrey, I may opt for the block type one from ebay. What made shy was reading here that the internal diameter is smaller inside, thus choking output. I googled your mjv3, I think you remember right about a product, but I can't figure it out. It is this one: http://www.clippard.com/part/MJV-3
I'd like a fairly small creation, currently playing with 16'' barrel and bigger chamber on GGDT. I think my mistake was the input of the flow coefficient 1.48 as cited on Humphey's data sheet. The results seem fine with 48 (%) in the text field. I get much higher muzzle velocity & energy when increasing caliber, and small increments when increasing barrel & chamber volume.

EDIT: I realizea slide valve is a 3 way valve, can be had for cheap and could easily fit a threaded nipple and then a schrader valve for filling. So slide valve or some premade 3 way one is more efficient?
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Re: QEV and building up

Unread postAuthor: jackssmirkingrevenge » Tue Sep 20, 2016 12:57 pm

Commercial QEVs are very efficient, to the extent that you don't need to be too worried about the efficiency of your pilot valve affecting performance, so go with whatever suits your configuration and budget best.
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