Portable Multi-Shot using a QEV and Schrader Valve Concept

[Binary Blue]

I'm sure this configuration has been discussed and attempted before.

Did I get this right?

I have the pressurized air reservoir and shrader valve on the "In" port of the QEV, a relatively small chamber attached to the "Out" port, and the barrel attached to the "Exhaust" port.

I have not drawn a loading mechanism, but it is not semi-automatic. I would likely try for bolt action, break-barrel, or even a Martini-Henry style configuration (even though it will be kind of difficult).

I plan on having the QEV stay "stock"--that is unmodded.

Will this design work?

[jackssmirkingrevenge]

Won't quite work as drawn. You have such a large air supply that the small amount of air lost to the schrader hammer setup will not be enough to fire the thing.

Have a look at this: http://www.spudfiles.com/forums/b2tb-sa ... 14817.html

You're better off modding the QEV and filling from the chamer side if you're going to bother with a momentary pilot.

Or just use a three way valve as a pilot: http://www.spudfiles.com/forums/semi-au ... 23626.html

[Binary Blue]

Thanks for the advice. How exactly do you mod the QEV?

And I've just placed an order for the slide valve and Chinese QEV from eBay as you suggested.

[jakethebeast]

I believe that if you make a SMALL (like 1mm) hole to the piston it should work, maybe a little spring behind it to help

[Brian the brain]

Woah..

A small hole in the piston?

yes...but not in the center and not to close to the outer edge.

That could have gone really wrong..

If you puncture the part that seals the outport, the piston is ruined!
I'd advise to stay clear of the edge to prevent tearing.

[Binary Blue]

Won't quite work as drawn. You have such a large air supply that the small amount of air lost to the schrader hammer setup will not be enough to fire the thing.

Have a look at this: http://www.spudfiles.com/forums/b2tb-sa ... 14817.html

You're better off modding the QEV and filling from the chamer side if you're going to bother with a momentary pilot.

Or just use a three way valve as a pilot: http://www.spudfiles.com/forums/semi-au ... 23626.html

If I use your (JSR's) under $20 Semi Auto method, will this BSPP to NPT adapter work with the female connections of the valves?

http://www.grainger.com/Grainger/ALPHA-Reducer-1CPD8

From what I understand, BSPP and BSPT are 2 different things (T is tapered, P is not).

Also, is the male end BSPP and the female end NPT?

From what this page:
http://www.pneumaticsolutions.com/inven ... Page4.html
says about model 82242 04 04 (I assume it's the same one listed on Grainger's site), the male end is BSPP and the female end is NPT.
Is this correct?

[jackssmirkingrevenge]

Not very clear in your link which is which, I would confirm with the manufacturer before ordering.


As to tapered fittings, IIRC non tapered male should fit in tapered female but not vice versa. A relatively cheap parallel tap and die set will let you convert tapered fittings to parallel ones.

[Binary Blue]

Not very clear in your link which is which, I would confirm with the manufacturer before ordering.


As to tapered fittings, IIRC non tapered male should fit in tapered female but not vice versa. A relatively cheap parallel tap and die set will let you convert tapered fittings to parallel ones.

I actually checked and found that it uses parallel threads so the adapter I've selected will work.

I used the same slide valve and QEV you selected in your $20 Semi Auto valve method (I matched the description in your pictures with the descriptions given by some sellers on eBay).

Specifically these ones:
Slide Valve:
http://www.ebay.com/itm/350648712367
QEV:
http://www.ebay.com/itm/300780603914

How long (measurement of distance) do you have to pull the slide valve handle to get it to open? I guess what I'm asking for could be referred to as the "trigger pull length".

I'm trying to design a trigger now and that statistic would really help.

[dewey-1]

How long (measurement of distance) do you have to pull the slide valve handle to get it to open? I guess what I'm asking for could be referred to as the "trigger pull length".
I'm trying to design a trigger now and that statistic would really help.

About 7 mm as determined from drawings made.

[jackssmirkingrevenge]

I don't have the part to hand but Dewey has the drawings made directly from it so I would take his word for it

The parts you ordered would appear to be a match for what I used for my demonstration model.

[Binary Blue]

Thanks for the dimensions. dewey-1, can I please also get the distance indicated in the attached image?

[Zeus]

2.5mm by me.

[dewey-1]

Hopefully this will suffice.
If someone can prove me wrong, let me know.

[Zeus]

Is that from the inside of the port, or from the outside? I'll strip down my QEV gun tomorrow and check both.

Keep in mind that these QEVs have some terrible flow restrictions, which can be drilled ouy, but it's a PITA. Still quite reasonable power at 500 psi though, knocks 1/3oz sinkers through 1" of pine.

[dewey-1]

The dimension that is really needed, is the hole center to the front edge.
The only difference in the valves is the port sizes as near as I can tell.
This side view shows why I disagree with 2.5mm.