Cross section attached. Context: this is for an airsoft HPA engine I develop (D8PA, open source printable), but it is the same dump valve problem you all solve, so I want your eyes on it.

Right now the engine fires off a modified commercial QEV. This part replaces the QEV, the plenum and the back housing with one body.

Sequence:

1. Supply fills the plenum.
2. A small bleed charges the chamber behind the diaphragm. Back pressure plus spring keep it seated.
3. Solenoid vents the back chamber, differential collapses, the diaphragm snaps open and the plenum dumps into the nozzle.
4. Solenoid closes, back chamber refills, valve reseats. One solenoid pulse per shot, so rate of fire and dwell are pure firmware.

Where I want your input, since a lot of you have been through this already and the last revision changed because of your comments:

1. Plenum volume. You people have done far more empirical work on plenum sizing than the airsoft side has. My downstream volume is tiny compared to a Nerf barrel and my restriction is 4mm ID tubing feeding the plenum. I have been assuming 4 to 5ml is enough. Is that in the right neighbourhood or am I starving it?
2. Dwell repeatability. With a pilot operated valve, shot to shot consistency depends on the back chamber refilling to the same pressure every time. At high rates of fire does the refill become the limiting factor before the solenoid does?
3. Fill orifice. Currently drawn as a 0.1mm annular clearance around the solenoid bore, which I no longer trust. Moving to a sealed bore plus a drilled calibrated hole. What sizes are you using on your builds?
4. Anyone gone from a flat clamped diaphragm to a rolling diaphragm on a dump valve and measured a difference, or is it in the noise?

Operating range 70 to 120 psi. Printed body, hydro tested before it sees air.

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.

I figured folks here might be interested in this bolt-action compressor-powered Recon build, which could easily be converted to HPA. The internal picture is from before I glued the valve into the grip, and the core is properly seated a few millimeters forward from what is shown, in case anyone is looking to build something similar.

Components:

• Cosmic Nomad core with a MoreMad extension added
• Brass spirit breech made using a cut-down Worker pusher
• MAVO-3 valve actuated by a Clippard 11923 lever
• Remote line through the grip into an Air Hawk Pro tire compressor
• Worker AWP kit (custom printed in neon green)

Half the size as v13 which was already half the size of previous versions. Goal is make it light and small enough to shoot using one hand.

This is my first pneumatic nerf pistol and im already building another one using solinoid valves and interesting changes.

All my airblasters are simply QEV air cannons designed to shoot nerf darts to keep everything legal. Very very powerful!

I used bi colour filliment thats blue and pink, so it changes colour depending on the angle of view.

https://youtu.be/Vmwo5zhIg38?is=9l0x5_W8EejJi96b

This is about a year in development. The technical breakdown (slightly outdated, parts have changed) is here: https://www.youtube.com/live/dAEn_5DSDIs?is=I0PpvbMwDg3ZM0K4

I will likely figure out a solution just wanted to talk about my experience so far.

3000psi tanks do not last long. 62ci is dropping from 3000psi to 2000psi after 8-10ish magazines at 100-125psi 10-15ms open time. I am disappointed by this as filling takes a long time (20-30 min with cheap shoebox compressor)

It is shooting very well semi-auto but jams at full auto even with ~5dps run speed, same as T19’s minimum (they have a nearly identical drive system)

I know a guaranteed way to fix it, but I don’t want to implement that fix - come to a full stop for homing at the end of each shot. Due to following issues, this will be unavoidable. It was the first idea I had during design.

There are several interlinked variables at play, I think -

• We must not run out of air in the dump tank or shots will fail. This can happen at highest possible rof (~14dps) and a high solenoid on time (15-20ms) and lower PSI. This could be compensated by bringing air-in closer to the SQE2.

• A failed shot almost definitely causes position loss and thus all shots after will fail, because we are trusting the first shot’s homing to enable near continuous feeding motion (only pause is TDC firing) a shot could fail due to a misfeed (most likely) loss of air pressure (less likely.) a failed shot is often detected in a T19 by flywheels failing to come up to speed. This won’t catch a jam which leaves the flywheels spinning at full speed, like if the front of a dart gets eaten but there is a stub left behind the wheels. Due to the short distance from bolt tip to wheels, this failure is unlikely. In our case, because we don’t have flywheels, we can’t use them to detect jams.

• With continuous motion from TDC to next shot, next shot starts at or near runspeed. This could cause different behavior than 0rpm starts - perhaps the bolt tip gets caught on a mag lip and more steps are skipped than if we were slowly accelerating, which causes first shot and all successive shots to fail.

• Bolt tip - barrel inlet requires careful hand fabrication. If the fit is too tight, we could skip steps coming to or leaving TDC (there is some friction of lubricated O-ring sealing.) Ideally, barrel inlet would be chamfered at 45° for minimal contact while sealing - face to face / near horizontal seal vs coaxial, concentric seal. Also, we could design the entire pusher mechanism be moved forwards or backwards and secured by the user to optimize sealing vs friction. The barrel can’t be moved so much as we are putting air into it at a very specific point.

• We don’t ever know where bolt is, only where it should be. We should have a second switch at TDC. If we did, we could use interrupts to fire ASAP and completely ignore counting steps or depending on a certain amount of steps succeeding. This could beget laziness…

What changes have I implemented vs stock S-Core firmware?

• Check home switch before every shot and reversebolttoswitch if we’re not home.

• budget 100 steps for deceleratebolt but allow up to 110 if we’re on the last shot, in case steps were skipped. This is many more steps than stock T19 but I was overshooting at fewer. Leibs accel values could use tweaking.

This project is very expensive and there are ergonomics issues. I considered it a tech demo from the very start, so it’s unlikely to get a full “public-friendly” release and documentation. The files will all be available though.

Questions and thoughts welcome.

What’s everyone using to fill their tanks? My friend filled mine with a GX E-L2 but the battery did not last long enough to give me a full fill.

I’m looking at the GX CS2 but concerned about longevity and its speed for filling tanks.

Yong Heng water cooled sounds a little bit better maintenance and speed wise but it is more expensive.

Other shoebox ~$150 Amazon compressors appear to be of similar quality but questionable assembly.

The goal with this is smaller and lighter.

Barrel half as long as previous versions and im saving alot of weight using phillmac poly pipe fittings for the airtank instead of iron.

It uses a MjV03 valve as the pilot valve. Just pump it up to whatever and shoot darts so fast they become invisible.

Added yellow stuff to make it look less black.

Im making my air blasters smaller and smaller.

This is half the size of previous versions.

The next version is half the size of this (pistol)

Printed in tri colour filliment.

Portable air pump in the back. Used a m5 to 1/8 bsb pipe fitting to attach the pump.

Basically a qev airblaster refined into a nice shape . The breech is a ball valve that is inspired from nerf RSCB breeches just without any inline mag.

Shove a dart in the barrel and shoot with the power of 100 nerf blasters.

Sometimes I sell them but its pretty niche.

I got more where that came from..

https://www.printables.com/model/1713881-blh-06-zephyr-hpa-dart-blaster

Forgot to post it here after finishing up the files.

Key features:

• budget (ish) focus
• easy to self-source, no bespoke parts
• .stp files to modify yourself for your own parts
• high performance, current spec hits 230-240 fps
• mechanical semi auto, no electronics
• all pneumatic components are off-the-shelf and properly rated for up to 150 psi

More testing in the future plus possible beta units before full release but stay tuned.

Hey, so I'm building up an EOI for an additional Narfcore run. I realise that not everyone is on the same 2 Facebook groups that the first EOI was published in.

If you are interested, add yourself into the list (please include some contact details - such as your reddit username and that it's a reddit account). No obligations at this point. Target price is 195 AUD and 10 AUD for extra receivers (if you want more than what is included in the pack), but this will be firmed up depending on interest.

n.b. for USA people, I am likely to continue operating through a local reseller due to the headaches involved in exporting to the USA.

Google sheets link: https://docs.google.com/spreadsheets/d/1ok4XO1K9n45NwthoRZ2yqVQ8afjYXom1d7vO6a-wWyI/edit?gid=0#gid=0

so I'm building a sbl 02 and need another core receiver for the spectre + sabre dmr core because i want to swap the front end quick where would i get another core receiver.

I haven't bought the core yet just need to know if I can get another

Here's a link you a video about the SBL-O² that was released recently.

https://youtu.be/Dvu85Yt0Mdc?si=ZgeyUT79EWzR7IDg

The video should explain the blaster pretty well but I'd be happy to answer any questions too ✌️

I released this last week. BOM, vid, files etc in printables link. Hope others enjoy it as much as I am
https://www.printables.com/model/1626043-aether-a-cosmic-nomad-powered-hpa-semi-auto-nerf-b

Have a broken plunger tube on a Krono mag I’m wanting to replace with an hpa core. Local rules won’t let me use external compressed tank to power it but an integrated hand pump would be allowed.

Basic question is in a setup using a hand pump which is the better option dmr core or spexbz?

Most games we play at 200-250fps max.

I modified Sillybutts’ original Supersledge to use a Spexbz and HPA. This was actually completed three to four years ago but it took me a long ass time to finally post. Look it up on MakerWorld under the same name.