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Directional Control Valve Actuated Qev

an efficient and powerful semi-auto valve assembly

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#1 Doom

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Posted 31 July 2008 - 12:33 PM

There are no single off the shelf valves which are adequate for semi-auto in Nerf guns. You can machine your own valve like Dr. Nerf's valve (edit: new link) or CaptainSlug's valves in APB5K and the unfinished ARR, but not everyone is willing or capable of machining. All these valves are functionally the same. A secondary chamber (and potentially an air cylinder) are pressurized and then separated from the primary chamber and vented out the barrel.

After a lot of thought and experimentation over a few weeks I decided on a combination of two off the shelf valves for semi-auto functionality. The advantages of this assembly are that it's efficient, powerful, relatively small, and very easy to build. The main disadvantage is the cost. I spent probably $45 alone on the assembly, which isn't too bad but more than I'd prefer.

The gun I built is for test purposes and will be recycled later. I don't have any stefans at the moment so I have tested with streamline darts. The range test was inconclusive because the streamline darts crap out after about 15 to 20 feet due to drag. It shoots streamline darts through cardboard at close range. If anything it's too powerful and I'll have to tone down the pressure from its current 40 PSI, reduce the pressure chamber volume, and start using weighted stefans to get use of the system.

To understand how the assembly works I'll link to guides explaining the individual components first. Spudfiles' page on QEVs explains their use and CaptainSlug had previously explained directional control valves. Read those pages and have a good idea of how those valves work before trying to understand how the assembly works.

Posted Image

The above image shows the entire test gun. I am using an HPA tank as the pressure source.

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This image and the one below use the same symbols CaptainSlug used in his directional control valve thread. The flat portion indicates flow stops there. I added arrows to show what direction the flow will be going in.

When the button on the directional control valve is not pressed the flow from the HPA tank goes through the QEV and into the air chamber. No air is leaving through the barrel or the exhaust port of the directional control valve.

Posted Image

When the button is pressed a few things happen. The system stops accepting air from the HPA tank. The air in the tubing between the QEV and the directional control valve is vented through the directional control valve's exhaust and that causes the QEV to exhaust its air out the barrel.

Basically, the chamber is filled when the trigger is not pressed and the chamber is emptied when it is depressed.

I'll be looking to get a video up to show how quickly the system works... it's really quite impressive. I can get through perhaps two cycles per second with this assembly. I was a little worried that the directional control valve I had wouldn't pilot the system well enough because they're designed for low flow but I think it's nearly perfect for the system.

I'll also get a parts list for the valve I have above soon too... to get you started the QEV and directional control valve are both available from McMaster-Carr and are part numbers 6646K11 and 6464K11 respectively.

Any questions, comments, hate speech, etc., are welcome. Normally I'd wait until I finished a gun to post about a development but I thought this valve assembly is too valuable to keep secret. Hopefully this will spark more development in air pressure guns.

Edit: To those who want to point out that my teflon tape looks excessive, that's what happens when you use the pink tape. It's only two layers if even that. The color and thickness of the tape is what makes it look obnoxious.

Edited by Doom, 09 March 2013 - 02:44 PM.
Added a link to replace an old broken one.

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#2 CaptainSlug

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Posted 31 July 2008 - 12:47 PM

Nice. QEV valves come in even larger sizes if a higher flow rate is desired.

Now we just need to know:
1. Your blast chamber volume
2. Your firing pressure level
3. Range average

I haven't had time to machine my own directional control valve, so it's likely that this type of configuration will end up in ARR (which was going to end up having 2 valves in it anyways).

Edited by CaptainSlug, 31 July 2008 - 12:51 PM.

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#3 Doom

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Posted 31 July 2008 - 12:50 PM

The volume of that chamber is about 10 ci but I don't intend to use it in a final gun. It was slapped together last night with available parts. The pressure of the tests were done at about 40 PSI. The range is inconclusive as I explained but I'd imagine it could easily be 100 feet or more with proper stefans. Give me a few days to make some and we'll have some precise figures.
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#4 jwasko

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Posted 31 July 2008 - 12:54 PM

Do you think that this could work using a "blast chamber" from a Hornet, Big Salvo, SMDTG, etc?

From my understanding, those blast chambers are set up in a way that is quite similar to your QEV.

Edited by jwasko, 31 July 2008 - 12:56 PM.

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#5 CaptainSlug

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Posted 31 July 2008 - 12:57 PM

Do you think that this could work using a "blast chamber" from a Hornet, Big Salvo, SMDTG, etc.

From my understanding, those blast chambers are set up in a way that is quite similar to your QEV.

The semi-auto blast chambers from those blasters are QEVs. You can use any kind of pilot valve you want to trigger them. Push-button, sleeve, ball, etc.

Edited by CaptainSlug, 31 July 2008 - 12:57 PM.

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#6 Guest_Just Some Bob_*

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Posted 31 July 2008 - 12:59 PM

Is the exhaust outlet from the DCV tappable, such that you could put that "pulse" of air to use too?

With a little timing work, that energy might be harnessed to advance a feed mechanism after firing.
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#7 jwasko

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Posted 31 July 2008 - 01:03 PM

The semi-auto blast chambers from those blasters are QEVs. You can use any kind of pilot valve you want to trigger them. Push-button, sleeve, ball, etc.

Yes, but what I meant was: could you achieve the "semi-auto" nature of Dooms test-gun, but replace the QEV and homemade airtank?

So, the setup would be [high capacity air tank]->[regulator, if HPA]->[directional control valve]->[Big Salvo blast chamber]

So then it would be: fill BS, press button/fire BS, release button/fill BS, press button/fire BS.

Of course, you would need to load darts, too.

It works in my mind, but I wanted to check with the experts.

Edited by jwasko, 31 July 2008 - 01:08 PM.

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#8 CaptainSlug

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Posted 31 July 2008 - 01:03 PM

Instead of the directional control valve recommended in the OP I would recommend part# 62475K11
Posted Image
It's cheaper ($8.90) and has twice the flow rate.

Is the exhaust outlet from the DCV tappable, such that you could put that "pulse" of air to use too?

With a little timing work, that energy might be harnessed to advance a feed mechanism after firing.

All of the ports on the Directional Control valve are threaded. But you would have to add volume inbetween the QEV pilot ports and the Directional Control Valve. However that's an extremely inefficient use of energy.

If you want to actuate something, do it with the air you will be firing the dart from. That's what I'm doing in my ARR design.
http://nerfhaven.com...?showtopic=9976
And i will be getting back to work on it sometime in September.

Edited by CaptainSlug, 31 July 2008 - 01:47 PM.

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#9 Doom

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Posted 31 July 2008 - 02:02 PM

One thing I'd like to note in general is that a smaller QEV (like the 1/4 inch size) should be plenty adequate for Nerf. If you want something slightly smaller I would suggest a 1/4 inch QEV.

Larger valves are a possibility too but the flow is so high that for a Nerf gun you'll probably see no real difference.

I haven't had time to machine my own directional control valve, so it's likely that this type of configuration will end up in ARR (which was going to end up having 2 valves in it anyways).


If you're considering it for ARR, that's be great. The main advantage to the assembly is that it's easy to build and I guess after machining many valves you'd want something that's easy to build.

Do you think that this could work using a "blast chamber" from a Hornet, Big Salvo, SMDTG, etc?

From my understanding, those blast chambers are set up in a way that is quite similar to your QEV.


I guess CaptainSlug answered your question. I don't know much about how those Nerf guns work, but if they're using similar valves I'd imagine adding a DCV and an HPA tank would be a great modification. Give it a try.

Is the exhaust outlet from the DCV tappable, such that you could put that "pulse" of air to use too?


As CaptainSlug said, the valve I'm using is threaded on all ports. I also made the pilot volume (the air between the pilot valve and QEV) as low as possible to pilot the valve faster. There's probably about 1/5 ci of air in there. Adding more would make the gun less efficient. It's best to actuate something either with the trigger pull or the main air chamber.

I don't know if CS was referring to the QEV being less efficient or the energy from the exhaust being inefficient though. Maybe he meant what I just explained.

Instead of the directional control valve recommended in the OP I would recommend part# 62475K11

It's cheaper ($8.90) and has twice the flow rate.


I actually asked McMaster-Carr about that exact part. The flow rate given is not for the exhaust, which is what matters in performance. They don't know the flow rate for the exhaust port or the diameter of it, but I would imagine the flow rate is higher than the 6 scfm of the valve I used.

You also would have to operate the valve differently (i.e. you would normally hold the button closed so air flows through and let go to shoot). To me it came down to saving a few bucks on the valve while spending more money on a spring to get the desired function. If you use that part too you'd need to get a 10-32 to 1/8 inch adapter which costs nearly as much as the valve. It's more expensive unless I'm mistaken about how the valve would work (it's possible I am).

Edited by Doom, 31 July 2008 - 02:41 PM.

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#10 Guest_Just Some Bob_*

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Posted 31 July 2008 - 02:03 PM

All of the ports on the Directional Control valve are threaded. But you would have to add volume inbetween the QEV pilot ports and the Directional Control Valve. However that's an extremely inefficient use of energy.

If you want to actuate something, do it with the air you will be firing the dart from. That's what I'm doing in my ARR design.


I guess we can disagree on that "efficiency".

In one case, I see it as air going to waste anyway. In the other, you would bleed some air which otherwise could have pushed your payload farther/faster.

It's true that to get enough energy in the "waste" air stream, one might have to add an additional chamber, but the advantage is that the payload gets the push from all of the main chamber's air. I personally don't want to size my main chamber bigger for anything other than higher performance.

But then again, I've hardly ever worked with payloads smaller than several ounces...
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#11 CaptainSlug

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Posted 31 July 2008 - 02:17 PM

The only thing I will have to add to DOOM's configuration for my purposes will be a flow control valve on the tank input so that I can control the fill rate of the air cylinder and blast chamber. I don't want the air cylinder refilling too quickly, or I'm likely to destroy darts.

It's true that to get enough energy in the "waste" air stream, one might have to add an additional chamber, but the advantage is that the payload gets the push from all of the main chamber's air. I personally don't want to size my main chamber bigger for anything other than higher performance.

I think you're missing my point. If you want to actuate something with pneumatics you use an air cylinder. An air cylinder applies a load when pressurized. So long as you pick an air cylinder with large ports it won't introduce any restriction to the volume you are using the fire the dart.
In the ARR design the spring-return air cylinder actuates a ramrod to load a dart into the barrel when the firing volume is pressurized. The pressurized air in the firing volume (which includes the air cylinder) is all used for firing the dart. That energy being released allows a spring to retract the ramrod so that the next dart can advance.

Making this cycle any more complex would lead to reduced efficiency. No potential energy is wasted.

Edited by CaptainSlug, 31 July 2008 - 02:20 PM.

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#12 Doom

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Posted 31 July 2008 - 02:46 PM

The only thing I will have to add to DOOM's configuration for my purposes will be a flow control valve on the tank input so that I can control the fill rate of the air cylinder and blast chamber. I don't want the air cylinder refilling too quickly, or I'm likely to destroy darts.


Good idea. While the flow rate isn't extremely high into the QEV it is faster than I anticipated.

Speaking of the air cylinder, where did you buy the one you used in ABP5K or what you plan to use in ARR? I'm looking at the ones at McMaster-Carr and they seem a little expensive so I'm wondering if you bought one elsewhere.

If you're making a CAD drawing with these parts, you can get the dimensions of the QEV and the DCV in the PDFs I just linked to. The width of the QEV in the first PDF is cut off--it's about 1.5 inches.

Edited by Doom, 31 July 2008 - 03:00 PM.

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#13 CaptainSlug

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Posted 31 July 2008 - 04:13 PM

The only thing I will have to add to DOOM's configuration for my purposes will be a flow control valve on the tank input so that I can control the fill rate of the air cylinder and blast chamber. I don't want the air cylinder refilling too quickly, or I'm likely to destroy darts.


Good idea. While the flow rate isn't extremely high into the QEV it is faster than I anticipated.

Speaking of the air cylinder, where did you buy the one you used in ABP5K or what you plan to use in ARR? I'm looking at the ones at McMaster-Carr and they seem a little expensive so I'm wondering if you bought one elsewhere.

If you're making a CAD drawing with these parts, you can get the dimensions of the QEV and the DCV in the PDFs I just linked to. The width of the QEV in the first PDF is cut off--it's about 1.5 inches.

The air cylinder I used in abp5k was in the parts bin at work. The one for ARR was ordered from Mcmaster (3/4" bore size with a 4 inch stroke)
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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

#14 Shadow 92

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Posted 31 July 2008 - 07:46 PM

Nice, I love semi-auto designs. I only wish I could get off my fat (120 lb) ass and make my own. :D

Edited by Shadow 92, 31 July 2008 - 07:47 PM.

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#15 Gyrvalcon

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Posted 31 July 2008 - 11:14 PM

Wow, this is great. As much fun as it is trying to make a decent valve system with PVC and a dremel, I like this even more.
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#16 Doom

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Posted 01 August 2008 - 09:12 PM

Glad you two like the valve configuration. I kept things as simple as possible, which meant avoiding anything requiring machining, so it's a very attractive setup compared against the ones requiring machining.

After some thought, I would suggest adding a check valve (one-way valve) between the HPA tank regulator and the DCV. When removing the HPA tank without a check valve the QEV will exhaust because of the flow path from the DCV to the now open regulator.

The plan at the moment is to make some stefans next week to take some reasonable range figures. I'll also make a video so some people could see how well the configuration cycles. After that I'll dismantle the test gun and start thinking about ergonomics and how to advance darts so I could make a serious Nerf gun.
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#17 King Of Butt Land

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Posted 01 August 2008 - 10:08 PM

That directional valve is pure sex for a semi auto design.

I'll be using it for sure on my new potato cannon.l

Edit: Damn, what I really need is one of these that can handle 300+ psi with ease.

Edited by King Of Butt Land, 02 August 2008 - 12:11 PM.

QUOTE(Puppy-žlayer @ Dec 18 2008, 04:22 AM) View Post

This contest may have some flaws, as people can simply be a deuschbag over the internet. By Lying.

A war-like setting/invitational would be better...


#18 Doom

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Posted 02 August 2008 - 01:33 PM

If you're looking to adapt this to a spud gun I'd suggest a higher flow pilot valve and/or a second QEV to pilot the larger one. Higher flow directional control valves are expensive. A 3-way ball valve should get you much more flow without the triggered operation though. McMaster-Carr part # 46095K51 looks only a bit more expensive than the valve used here and should work great in a spud gun. That actually sounds nice and I think I'll try making it eventually...

3-way ball valves are good for high pressures. You'd have to find higher pressure QEVs too and I'm not sure if those are made. A correctly made piston valve should have the same functionality, but that'd involve machining, which I tried to avoid.

Edited by Doom, 02 August 2008 - 04:55 PM.

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#19 King Of Butt Land

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Posted 02 August 2008 - 03:43 PM

Most QEVs are safe up to atleast 400 psi. Some guy has taken his repeatedly op to 800 with no damage.
QUOTE(Puppy-žlayer @ Dec 18 2008, 04:22 AM) View Post

This contest may have some flaws, as people can simply be a deuschbag over the internet. By Lying.

A war-like setting/invitational would be better...



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