SpudFiles

This is my idea for a new hybrid valve design. I am new to potato guns so I dont know much about this stuff, but the idea is simple. Just put a wire on the end of the working of the valve, so when the valve fully opens it completes a circuit to a stun gun igniting the still pressurized fuel air mixture. Hopefully allowing for quicker reloads because of no wasted time spent on replacing burst discs. Sorry if someone else already had this idea I hope it helps someone .

This makes little sense to me...
How does the valve fully open?
What type of valve is it?
Why are you igniting the fuel after the valve has opened?

A picture might help.

I would want the valve to open before the fuel ignites so that there is no chance of the valve getting stuck from the pressure of the combustion making the chamber explode. Any valve type will work as long as the moving parts are a metal so the circuit can be completed. I was planning on using a valve from a garden hose dual output thing wrapped in fiberglass for safety and looks attached to an electric motor like a drill. Sorry I don't have a picture at the moment

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I see, I thought that if I opened the valve quickly enough that it would still get to the peak pressure by using a long barrel providing maximum velocity.
I don't really want high acceleration I want high velocity. Do you think it would increase velocity if I moved the contact to the start of the valve just after it starts to open? That would allow more pressure to be generated inside of the chamber

Bottom line, it is too slow. By the time any valve has opened fully, the mix would be well on the way to being depresurized.

You may know, but a burst disk is by far the simplistic approach.

"Since Burst disks only last for a single shot and need to be replaced before each round"

^This is the only dis-advantage of a burst disk. To begin with: we know that we can't build a valve to out perform a burst disk. From the article you can see all you need is a union and dependently a few layers of aluminum foil.

If your looking for ROF I've always thought making a little aluminum foil burst disk loader.

If you don't want a burst disk and want to reload quickly, make a piston valved hybrid. Piston valves are not quite as quick as burst disks, but they are a good alternative. Your design would probably work with a modded sprinkler valve, but much of the air pressure would be lost before ignition.

You must remember that I will be using a ramped up drill motor or a pneumatic i think its called a servo? to open this so that it will open fast enough. Also I have revised it so that the fuel is ignited before the valve opens all the way .

At least if it doesn't work it will look impressive.

ThegunGuy wrote:You must remember that I will be using a ramped up drill motor or a pneumatic i think its called a servo? to open this so that it will open fast enough. Also I have revised it so that the fuel is ignited before the valve opens all the way .

At least if it doesn't work it will look impressive.

If you are driving the valve with a drill motor and it can start instantly (it can't) then using the drill RPM you can find the time for revolutions per second. A 1/4 turn valve will open in 1/4 revolution or 1/4 the time for a full revolution.

Most cordless drills have a maximum speed of 2,000 RPM or less. That's 33-1/3 revolutions/second. Inverting gives 30 ms per revolution. A 1/4 revolution is therefore 7.5 ms. This assumes the drill starts at full speed instantly. Real world acceleration is orders of magnitude slower.

My Marshmallow cannon completely vents the chamber in about 15ms. At least 2/3rds of the pressure is gone in 7.5 ms. The rotary actuator simply isn't fast enough.

Look for a valve that opens in under 1 ms for a hybrid. Either a burst disk , diaphragm or light piston opened by the rising chamber pressure is the only way to do this.

Thanks for the advice.

By looking at the picture I don't see any possible way for the valve to open in any timely fashion. Either it will get jammed by the chamber pressure pushing on it and it won't open at all, or it will open prior to ignition resulting in a weak, premature combustion. The combustion will need at least some resistance prior to being released in order for it to complete. The valve opening and then the combustion taking place is not ideal. I am willing to bet it would still be more powerful than a regular combustion assuming the barrel is long enough or the projectile is heavy enough, but much potential will be wasted.

Now consider this. I see a way for your valve to work and it might prove to be one hell of a design in fact. If you can offset the axis of the valve so that the combustion causes it to rotate open, like a revolving door, then this could work. You could have a spring or ball detent to provide the resistance and the blast will spin the valve open. It would just need to be prevented from actually spinning so it only turns the required 90 degrees or whatever it needs to be to open.

That sounds great and give me another idea I will oversize it to be barrel size and add a shotgun magazine extension to the side it so when the valve closes it chambers a round to be rotated and be ready to shoot when the valve opens again. Then I will change the contact to release the first valve on the refueling line and when the valve closes by spring it the second valve on the fuel line releasing the fuel and compressed air into the chamber.
Making it a semi auto hybrid.

You can often outperform a burst disk. For once I'll preach the qdv. The opening time is a little higher, though the disk causes gigantic turbulence (edges left around) and may not completely burst every single time.

The QDV is just as reliable, easier to trigger and requires no replacement every shot. For hybrid adaption you could put a 1x (atmospheric mix) between the projectile and piston, opening the piston and igniting the hybrid mix.

inonickname wrote:You can often outperform a burst disk. For once I'll preach the qdv. The opening time is a little higher, though the disk causes gigantic turbulence (edges left around) and may not completely burst every single time.

The QDV is just as reliable, easier to trigger and requires no replacement every shot. For hybrid adaption you could put a 1x (atmospheric mix) between the projectile and piston, opening the piston and igniting the hybrid mix.

As strange as it sound from me, I advise against a QDV in a hybrid. If the 1X mix is used to open the valve and then light the main mix, the main mix begins burning after the projectile has started motion. The main mix also ignites after the valve opens. Both are bad for performance.

Very close to the QDV is the traditional piston valve. Upon a sudden rise in chamber pressure from combustion, these open after the combustion is well underway and thus provide higher initial pressure on the projectile for the valuable early acceleration pressure on the projectile. Remember, most of the acceleration happens in the first half of travel in the barrel.

If a QDV is considered, a 1X mix and the main chamber mix could be ignited at the same time so the chamber pressure builds while the valve is opening.