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Magnetic Pulse Valve

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Magnetic Pulse Valve

Unread postAuthor: ONEWING » Thu Mar 18, 2010 7:59 am

I came into this forum a few days ago with an idea in mind to make a pulsing valve/bolt by having a piston held in place with permanent magnets. I had a look around and I did find various attempts to make something very simular (looking at you Jack) except the attempts used springs to hold the piston in place.

I propose that the springs are inherently flawed by the fact that they are at their weakest when actually in the closed position instead of their strongest meaning as they start to move open the air pressure against them decreases but the pressure holding them closed increases, resulting in a fart to use jacks term.

Magnets operate the opposite way, exponentially decreasing the force closing the valve as the air pushes it apart allowing the rapidly decreasing pressure to fully open the valve.

So by using two ring magnets it may be possible to make a working pulsing valve/bolt. The only possible problem is that the "filling air" may still exert enought pressure to keep it open if it moves too far so a combination of magnet and spring may be in order, or even a pushing magnet of the same pole placed behind it to "rebound" off.

A rubber washer acts to make a seal between the magnets and prevents them shattering on one another, varying the thickness of this will tune it in to fire at differing pressures.

So the pressure builds up behind the magnet valve until it blows, pushes bolt forward chambering a BB and firing it off, the pressure in air chamber decreases, magnets fly back together (maybe aided by "rebound magnet") and it repeats.

Now I was going to just make this and see what happens but I'll chuck the idea out there for people to ponder, try ect.
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Unread postAuthor: POLAND_SPUD » Thu Mar 18, 2010 8:17 am

hmm that's an interesting concept... it seems logical
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 18, 2010 8:51 am

I flirted with an idea conceptuallyhere where basically the spring is replaced with a solenoid, where the bolt would be forced to move externally.

Image

The main turn-off was the requirement for a seperate electric circuit to power the unit when I was looking for a system that could work on one air supply (as I eventually did ;)) however your idea using permanent magnets makes sense. One thing I would change in your diagram is making the piston wider to ensure that it "pops" open effectively, have a look here for some pointers ;)
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Unread postAuthor: Lockednloaded » Thu Mar 18, 2010 11:45 am

would a strong enough magnet be air tight?
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 18, 2010 12:09 pm

Lockednloaded wrote:would a strong enough magnet be air tight?


You can have a thin layer of rubber between them ;)
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Unread postAuthor: ONEWING » Thu Mar 18, 2010 8:05 pm

A good start would be 7/8" ring sandwiched between a 3/4" endcap and a fitting to hold it in place and a 5/8" piston. The only 7/8" magnet I could find had a .172" hole (about the same width as barrel) thus .023" square area for the air to push against. Say you want it to fire at 100psi the magnets only have to have a holding force of 2.3 pounds or about the weight of 1 litre of milk.

Let two disk magnets join, then try pull them apart without sliding or lifting one edge they will easily have enough force to hold back quite a high pressure. Air only has the inner open ring to push against. You'll need rubber not only to seal it but to lower their strength and also to prevent them shattering because they are so brittle.
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Unread postAuthor: Duane31 » Thu Mar 18, 2010 9:22 pm

It's a neat concept, but don't forget about the forces of air pressure, which will be far greater than the gauss of the magnet. Springs are indeed the best solution. Reasons are obvious. For example, think of a spring, size aside for a moment, that yields, not produces (key word) a resistance of 100 pounds. One hundred pounds of spring pressure equates proportionately to air pressure. The magnets you will need will have to have a gauss rating not realistic to their real size. To give you and idea of gauss scales: Average refrigerator magnets yields 50 gauss which has a holding power of about 14 grams.

Electro-magnets are area of discussion.

Why not just use a "Viking" brand air horn solenoid? It is an electromagnetic operated valve that is very small and will work up to 150 psi. With some tinkering it can and will do the task of your schematic.

Do some research on types of magnets and their gauss rating and you will walk away enlightened and possibly changing your mind.

The spring will never go away. They are simple, practical, nearly fool proof, compact, and very reliable.

I say this because I did come up with a functioning valve design that your schematic entails - with 20,000 gauss rated magnets it will only work on 20 psi.
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Unread postAuthor: ONEWING » Thu Mar 18, 2010 9:45 pm

I dare say you are very wrong, for the reasoning look at my immediate prior post. Obviously we aren't talking fridge magnets here.
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Unread postAuthor: Lentamentalisk » Thu Mar 18, 2010 10:52 pm

No, ONEWING, his physics seems about right (I haven't done the math though.)
Air pressure is truly frightening when you think about it. 150psi may seem like not very much for a cannon, but if you were to stand on a piston made out of tennis balls shoved down a cannon packing 150psi, you would go FLYING. Even on objects much smaller, such as a 6mm BB, 150psi weighs in at 27lbs of force. That is the equivalent of more than 3 gallons of water, pushing down on a single BB. Now think about how most pellet guns operate more on the range of 500-1000psi. Balancing a piston with air pressure is almost always going to be the best solution.
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Unread postAuthor: ONEWING » Fri Mar 19, 2010 12:03 am

Ho humm... I've already done the math its in the post that no one seems to want to read or refer too. 115-90 psi shop compressor pressures acting on .177 BB, I'm saying its easily handled, do the math based on this example.

Yes its size and pressure limited, unless you go to rediculous magnet width (assuming one doesnt want to use a 2" magnet with a 1/4" bore at 1000psi) but thats just inherent to the design you have to work with it.

EDIT: Even your 27 pound force example can be handled by a relatively weak 3/4" magnet and this is magnet on steel not magnet on magnet. http://www.kjmagnetics.com/proddetail.a ... M%2DE%2D20
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Unread postAuthor: Lentamentalisk » Fri Mar 19, 2010 12:25 am

Wow, look at that fail on my part... I forgot to turn diameter to radius before squaring... Ok, that seems a little more reasonable.
Mea culpa.
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Unread postAuthor: Duane31 » Fri Mar 19, 2010 12:31 am

Well, I'm no newbie when it comes to airguns or the principle laws required to propel objects. :roll:

Fridge magnets were used as an example for Gauss scale. For real fun look up how to build a "gauss rifle". You can do it with a wooden ruler six 1cm square neodynium magnets (1,000 gauss), and steel ball bearings. It's a neat project.

If you get your idea to work and have the RECIPROCATING effect using magnets by all means let us know ASAP. I'm tellin' ya, once the air flow is kicked on those magnets will never reciprocate, nor will they have the energy to close unless the air supply is turned off. If the magnets are holding closed with, lets say 10 pounds of force (an example only), anything less than 10 psi will never open it; anything greater will simply keep it open. It's simple, really. Springs do not have a constant hold like magnets - it is progressive; it's a liner principle; point A (not compressed) and point B (compressed).

Your schematic is correct, but it is missing a key point.

The way I got mine to work, your missing point, is this: your ram/BB pusher needs to have a means of sealing off the valve inlet hole when it reaches optimum forward travel. This way the gas that did get through will propel the projectile and will be gone leaving a voided valve that has no other option than to close to start the cycle again.

It's not the magnet idea that is flawed - it sounds great.

How about this: A pneumatic air rifle's inlet, or check valve as it is called. No matter what spring you use in the valve it will never 'flutter' (a RECIPROCATING effect); a light spring makes pump strokes easier while a heavier sprigs makes the pump stroke harder (resistance upon resistance). A magnet in place of a spring hasn't changed anything as far as principle goes. Neither will it ever reciprocate or flutter.

As a secondary valve it is great for a single shot platform, but not a BBMG. A first stage valve releasing its burst of air/gas/pressure source into your device would make a great single shot or semi (double action semi) platform.
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Unread postAuthor: Lentamentalisk » Fri Mar 19, 2010 12:46 am

No, the concept is to have the air going into the chamber restricted.
The pressure builds, pops the magnet, which opens very quickly, dumping all the air, and letting the magnet close the valve again.
Rinse and repeat.

It is exactly like Jack's pop-off bbmg, just with in theory, better valve opening characteristics. A valve returned by a magnet could, in theory not have the "farting" problems that Jack's cannons were having.
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Unread postAuthor: ONEWING » Fri Mar 19, 2010 12:54 am

Heh yeh I'll let you know :P The thing is this only has merit if its simple, theres plenty of complex ways of pulsing air but this is an attempt to make it as simple as possible with 1 moving part forming valve and bolt any more complex aint acceptable.

I have recognised the problem of the valve vibrating in the open position (as the spring version would vibrate in the closed position ie. fart) Thus the rebound magnet *possibly* alleviating that.

I'm confident of reciprocation, I think the point your missing is that the air entering the chamber behind the magnet valve is of a more restricted flow then that exiting it. You will get a pulsing action, whether or not the piston has maximum back and forward travel is another thing open for experimentation.

EDIT: yeh I was slow on the reply but as stated Lentamentalisk, same point.
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 19, 2010 1:39 am

Lentamentalisk wrote:A valve returned by a magnet could, in theory not have the "farting" problems that Jack's cannons were having.


A sprung pop-off valve with the following oft-repeated characteristics will not fart:

- Piston substantially bigger that the seat
- outlet port smaller than seat
- outlet port exposed after minimal piston movement

I have enough working prototypes to prove that :P

Modified pop-off valve

custom pop-off v1.0

custom pop-off v2.0

custom pop-off v3.0

marble autocannon


I think the application of magnets could potentially make my original blow-forward designs like this one and this one work as constant flow autos.
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