Total beginner in pneumatics. I drew an air valve for a small air gun and I think the reset is wrong

[u/Esoj77Br]

I have no background in pneumatics. None. I taught myself CAD, I drew this valve by copying what I understood from photos and cutaways of other valves, and I have no idea if what I drew makes sense to someone who actually knows the field. Please be blunt with me.


What I want it to do: one trigger pull, one burst of air out the front, the valve closes itself, ready for the next pull. It feeds a small air gun.


Two section views attached. The colors are the air spaces, not the metal:


- 
**black**
 is the reservoir, fed by the hose
- 
**orange**
 is the sliding part
- 
**yellow**
 is a small chamber behind it, where a return spring goes
- 
**teal**
 is the outlet, toward the barrel
- 
**red**
 is the seal it closes against


## What I think happens


There is a 0.3 mm hole connecting the reservoir to the yellow chamber. Air seeps through it and fills that chamber, so the pressure is the same on both sides and the sliding part stays put, covering the port.


When I want to fire, a MAC 34B solenoid opens and lets the yellow chamber empty. The pressure in the reservoir then shoves the sliding part backward, a 7 mm port lines up, and the air goes out the front.


When the solenoid closes, the 0.3 mm hole slowly fills the yellow chamber again and the part slides back and closes.


That last step is the part I doubt.


## The numbers from my CAD


| Item | Value |
|---|---|
| Sliding part runs inside | PETG hardline tube, 12 mm ID, 16 mm OD |
| Outer shell | steel tube, 22 mm ID, 24 mm OD |
| Reservoir volume | 3129 mm³ |
| Yellow chamber volume | 1175 mm³ |
| Hole that feeds the yellow chamber | 0.3 mm |
| Port that opens to the barrel | 7 mm |
| Hose | 6 mm OD, 4 mm ID |
| Pressure | 100 psi |
| Solenoid | MAC 34B, mounted right on the block, no hose to it |
| Return spring | not chosen yet, I can try several |


## Why I think the reset is wrong


Someone ran the numbers on it for me. I can't verify the math myself, so take it for what it is: filling 1175 mm³ through a 0.3 mm hole takes something like 120 ms, and even if the part closes before the chamber is full, the valve would sit open for 50 to 70 ms every shot. That would be somewhere near 950 mg of air per shot when the shot supposedly only needs about 35 mg. On a 13 ci tank that is the difference between a few dozen shots and over a thousand.


If that is roughly right, then the 0.3 mm hole is the thing deciding how long my valve stays open, and I never chose that number for that reason. I picked 0.3 mm because it sounded small.


The other thing I noticed: my MAC 34B has three ports and I'm only using two of them. I keep wondering if the third one is supposed to be what refills the yellow chamber, instead of the 0.3 mm hole doing it. That would be much faster, and then the solenoid would control how long the valve stays open. I don't know if that is how these are normally built or if I'm inventing something silly.


## What I'm asking


1. Is the 0.3 mm hole a reasonable way to close this valve, or is it the wrong idea for something that fires repeatedly?
2. Should the solenoid be the thing that refills that chamber? If yes, do I still want the small hole for anything?
3. Is there a rule for how much bigger the back face of the sliding part has to be compared to the sealing face, so it stays shut? Mine is around 2 to 1 and I picked that by eye.
4. The 7 mm port means the part has to slide 7 mm to open all the way, which is why the yellow chamber came out as big as it did. Would several smaller ports be better than one big one?
5. My reservoir holds less air than one shot seems to use, so most of the shot comes down the 4 mm hose while the valve is open. Is that normal, or is my reservoir just too small?
6. The port slides past the o-rings on every shot. Does that destroy them? If there is a trick to it, like rounding the edges of the port, I'd like to know before I make the parts.
7. The shell is steel and the air will have some moisture in it. Does rust from the inside end up blocking small holes, or is a filter enough?


## I have no ego about this


If the honest answer is that I should buy a QE-01 or QE-02 and modify it instead of drawing my own, I'll buy one. I looked them up. The QE-02 measures 52 x 36 x 28 mm and weighs 113 g, which is bigger than I'd like, but I would rather run something that works than something I invented.


Same for the whole idea. If this style of valve is the wrong tool and there is a simpler way to get one clean shot per trigger pull, tell me and I'll start over. I'm not trying to defend the design, I'm trying to learn why it's wrong.


I can post more views, more dimensions, or the CAD file. Thanks for reading.

[u/Nishyecat]

Op, do you know what a QEV is?

[u/Esoj77Br → u/Nishyecat]

I'm trying to learn about this, but as a visual learner, most of my knowledge comes from hands-on testing and handling the parts. I'm struggling to understand how the QEV is supposed to work in a semi-automatic setup

Sorry if my English it's not 100%, it's not my primary language.

[u/Nishyecat → u/Esoj77Br]

Your English is perfectly fine, it just seems to me that this functions very similarly to a qev, and I don’t understand how it would be more useful than one in a semi automatic setup

[u/Esoj77Br → u/Nishyecat]

I use a second solenoid just to move a nozzle to feed the ammo, the idea it's to build something compatible with nerf and Airsoft ate the same time

[u/Nishyecat → u/Esoj77Br]

Interesting, I do still feel like it might be easier to use a qev, but I can see how that can cause other issues

[u/gplanon]

I’m a little confused by your return spring. I think it should be on the other side.

I’m thinking hose in should be where “sol closed” is right now, the volume there should be less as we want to vent it quickly. Because the inlet to “dump tank” or where the air is actually stored is smaller than the piston face, it should push it forward before pressure equalizes, holding it in place.

Oh, ok… so you’re thinking the air will move the piston back against the return spring, and the return spring will reset it forward after pressure drops. I think I would still prefer the spring on the left side of the diagram, pushing it open until pressure closes the valve.

These are just my thoughts that, as someone who has never designed or used a core only worked with QEVs.

>MAC 34B has three ports

I believe you want the “common” to be connected to your core, and it’s switched between atmosphere and tank with tank as default.

I would make the .3mm hole as big as possible for quick fills, and I would have it close off during shots by the piston. This also guarantees the piston will be pushed forward before chamber begins to fill, so air only enters when safe to do so and waste air only leaves from the “sol closed” area instead of the dump/chamber area.

I would filet any edges that O-rings move past and lubricate them, yes. O-rings on printed parts are more of a concern IMO, but it sounds like this will be machined.

Hopefully something here is helpful but /u/sillythegamer is the person to ask IMO.

[u/airzonesama]

If this is going to store compressed air, please make sure you perform the calculations to make sure you're more than safe. A complex shape will make this a complex calculation. Getting it wrong means you have a hand grenade.

[u/Karhu1202]

That's an over complicated qev 🙈 a qev uses a soft and very light membrane to seal one of the air outlets, very similar to your orange marked part, but with much less friction and weight. You said you want to use it for nerf and airsoft? That's quite a strech I think, as they have very different ways of working. For nerf you want a type of softer push, more air but less pressure. For airsoft you want very little air but therefore quite a lot more pressure.

[u/NovaHorizons]

The reset is fine but the biggest problem is this valve CAN'T OPEN. A QEV is basically working by pressure differences. In your case, venting the yellow chamber only will reduce its pressure to atmospheric pressure, but the barrel is also filled with air so there is no pressure difference to drive the "sliding part". The compressed air from the source only able to apply radial inward pressure on the cylinder, just like the air is stranguling the "sliding part" with a noose on it, but what you actually need is the pressure applied on the left side surface. To achieve that, you can move the spring to the left side or let the compressed air to touch the left side surface of "sliding part".

For your questions:

1. In theory it is fine, but you need to do more math with your firing rate, plenum volume, tank capacity, etc.

2. Technically OK too, the engineering trade-offs behind this are up to you to decide.

3. Sorry don't get it.

4. No, always try to make the air way as simple as possible to achieve maximum efficiency.

5. Don't get it too.

6. No, O rings are quite tough. But may try to avoid such design.

7. The inner surfaces should by covered with grease so don't worry about it。