QEV and building up

[KnooBill]

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.

[Doodmens]

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 ... SwdzVXkyPy

Have you chosen a pilot valve yet?

[Ianbuckwell]

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

[KnooBill]

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?

[jackssmirkingrevenge]

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.

[KnooBill]

The items from China arrived! Missing two plumbing parts currently, but I can source then locally. Most difficult was finding a shop with jointless pipes and turning threads.

I have some trouble understanding pumps. My approach is to first find a pump and then install the appropriate valve. The QEV will be piloted by 1/2" slide valve. Seeing that those QEVs can easily withstand 400-500 psi, what pump would you suggest and what type of valve? I can't fully understand all the pump types and which is appropriate, pcp, 3 stage, quick disconnect etc. So the goal is a pump that can reach 400- 500 psi range, decent build quality, won't take forever to fill a chamber of 1" by 10" (approximate, barrel is 0,5*19,5) and an attachable valve for the purpose at the end of the slide valve. Any suggestions?

[KnooBill]

Hello, I have made a working prototype, it was put together, painted and dry fired. I cannot get it on my 240psi pump to go over 140psi. Could I buy something to install on the pump to increase pressure without needing a heavier person? I'm now researching a quality trigger mechanism, and swapping out the reservoir for a curvier one to work as a handle.
How much would it lessen performance if the barrel choked more and the reservoir was more curvy?



I'm also considering multishot, which schematic would work? Where should a pressure gauge be placed? The goal is to have some powerful shots. As I understand it the ball valve should be open, the chamber filled, then closed, fire. Then the second shot open & close ball valve, fire. Would the second schematic need a ball valve or similar to separate [air intake valve-T-reservoir]?


Would there be other ways with off the self parts to achieve multishot (possibly by swapping out the slide valve in schematic 1)?

[jackssmirkingrevenge]

Could I buy something to install on the pump to increase pressure without needing a heavier person?

How about a proper pump?

Something like this isn't too expensive and can reach higher pressures than you need.

How much would it lessen performance if the barrel choked more and the reservoir was more curvy?

A contorted path for the air typically reduces performance, but not to the extent that you'd see without a chrony. The "barrel choking flow" warning you get on GGDT simply means that your valve flow is higher than what can go through the barrel - so yes, you would get better performance with a larger diameter barrel in terms of energy, but on the other hand if you're happy with your chosen caliber that just means your valve is more than good enough.

This is the ideal setup because it refills the firing chamber when you push the slide valve forward, and fires while automatically closing off the reservoir when you pull the slide valve back. No need to mess around with ball valves. Note however that the more pressure you have, the more difficult the slide valve is going to be to operate.

[encohen]

I'm also considering multishot, which schematic would work?

I would take JSR advice and go with the second schematic. I got 2 QEV+Slide valves multishots combos, both working great at 550 PSI - no ball valves.

Where should a pressure gauge be placed?

you can get a tee and connect it to the air chamber on one side and a pressure gauge on the other, this way you can alway see the pressure for your next shot.

The goal is to have some powerful shots

if you are after multi, consistent & powerful shots i would get a paintball tank with a regulator & a remote line. That will allow you to connect a constant and consistent air supply to the rifle and get lots of shots (depending on pressure & chamber size). you will however need a PCP pump, like the one JSR suggested.

however that the more pressure you have, the more difficult the slide valve is going to be to operate.

That's correct but you can use some silicone grease to make it slide smoothly.

[KnooBill]

Many thanks for your replies, I dearly appreciate them. I am drawing up a final schematic based on the AIR-T/RES-SLIDE-QEV/CHAMB setup, which will look both visually pleasing and incude triggering. Would you know if it would be better to use compression or extension springs on the slide valve for fastest opening? The spring loaded slide valve will be locked in place by a trigger.
My regards to the pioneers.

[encohen]

I'm really not sure about which spring would work best. I didn't use any spring for the slide valve.

[jackssmirkingrevenge]

Would you know if it would be better to use compression or extension springs on the slide valve for fastest opening? The spring loaded slide valve will be locked in place by a trigger.

I would use a compression spring, something like this: