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The FGV - would that work?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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The FGV - would that work?

Unread postAuthor: dongfang » Fri May 16, 2008 7:03 am

Hi,

I just thought if combining some elements from the DFTV valve with some from a common gate valve (which is otherwise useless for spudding - too slow).

At rest and charged, the friction of the gate plate against the barrel's seal is enough to keep the bolt assembly in place (there is some downward force on it from the pressure delta across the lower piston).

When triggered (by letting a little air excape through the trigger line), the will be a pressure difference across the upper piston. This will make the lower piston unseat, increasing the difference - and the acceleration downwards of the bolt. Of course there should be a bumper, as usual.

Advantage: Linear flow. It's a 0 degree coaxial. Nice if you don't want the air to go around corners, or you want a chamber-valve-barrel configuration.

Disadvantages: ?? Maybe not easy to get to seat when charging.

What do u think?

Regards
Soren
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Unread postAuthor: jrrdw » Fri May 16, 2008 8:03 am

So you have a piston valve pulling a gate valve. To many moving parts, by the time the gate valve is all the way open the projectile will have all ready left the barrel.

Uneek in design, but not practical.
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Unread postAuthor: willarddaniels » Fri May 16, 2008 8:19 am

jrrdw wrote:So you have a piston valve pulling a gate valve. To many moving parts, by the time the gate valve is all the way open the projectile will have all ready left the barrel.

Uneek in design, but not practical.


Not so. There is only one moving part, as the gate and piston are connected and move in unison, in one, linear direction.

I like the idea, but I think the biggest problem you will have is the friction between the seal and the gate. Even lubed up, there will be a lot of force on it and it either may not open up as much as you want it to or it will severely weaken your linkage between your two main components. ...unless the piston is a bit larger than the barrel d and pulls the gate 95% open every time. (1.5" piston, .5" barrel)

You are right, it may be difficult to get a good seal, but if you channelled the gate to seat it, it shouldn't be a problem. Try to construct it so you can lube it easily, maybe a grease zerk would work well there.

So, 3 points: proper lubrication, ensure it will open "fully", and piston:gate ratio.
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Unread postAuthor: jimmy101 » Fri May 16, 2008 10:35 am

I agree with jrrdw, interesting design but I think it'll be too slow to be practical.

Lets see, assuming the barrel is 2" and you want to the valve to open in 1mS, the gate has to move at 2/12/0.001=167 FPS. That's pretty fast. In addition, since the gate has to move the full barrel diameter, it's going to take a heck of a bumber to keep the valve from destroying itself.

Add in the large amount of friction and the fact that partial opening of the valve doesn't help the valve open further (like most barrel sealing valves) and I think the perfomance will be disappointing.
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Unread postAuthor: dongfang » Fri May 16, 2008 11:19 am

Hi,

Yeah I'm aware that it will need to move rather fast.

Hmm I wonder which (large) valves will open in 1 mS? A piston valve would need about 1/pi times the speed of this one (assuming that about half the barrel circumference is open towards the chamber, the rest is facing the tee wall).

Well the partial opening will help it open faster: The lower piston pops open and reduces the pressure in the pilot chamber further. The back pressure from the projectile reduces force on the gate, and friction.

Regards
Soren
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Unread postAuthor: koolaidman » Fri May 16, 2008 4:20 pm

Wow, very intriguing idea. I very much like the idea of a fast perfectly linear valve. definately lube the gate seal. I also, like the idea of triggering the piston, and having it dump even more pressure once it moves.
The problem i forsee, is keeping the piston from moving until piloted. You need to have that frictional force (from orings?) keeping it in place, but having a small force from pressure overcoming its static friction. It's very possible, im just saying you'll need a good balance of friction.
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Unread postAuthor: clide » Fri May 16, 2008 6:39 pm

Nice design. I think it could work, but there may be some issues to deal with. As koolaidman pointed out, the piston will be trying to pull down when pressurized and the only thing keeping it shut will be the friction on the seal which may create some difficulties getting it to seal in the first place.

Second you may have some issues getting a seal like that to stay in place. That sideways jerking motion under high force isn't very friendly to seals may present some problems.

I was originally thinking of something like this before I made my valve with the angled piston and seat. On a related note I've got a valve that accomplishes a similar configuration goal...I really need to stop being lazy and get my stuff posted.
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Unread postAuthor: psycix » Sat May 17, 2008 3:50 pm

jimmy101 wrote:I agree with jrrdw, interesting design but I think it'll be too slow to be practical.

Lets see, assuming the barrel is 2" and you want to the valve to open in 1mS, the gate has to move at 2/12/0.001=167 FPS. That's pretty fast. In addition, since the gate has to move the full barrel diameter, it's going to take a heck of a bumber to keep the valve from destroying itself.

Add in the large amount of friction and the fact that partial opening of the valve doesn't help the valve open further (like most barrel sealing valves) and I think the perfomance will be disappointing.


That COULD be achieved when you make the lower piston travel a long way to accelerate and then hammer open the gate valve. The piston should not yet be attached to the rod, but the rod has an stopper, wich it would hammer against. Then the rod pulls at the gate valve itself.
But this would be inefficient and put alot of stress on the materials.

You could better just construct a normal piston valve right?
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Unread postAuthor: dongfang » Mon May 19, 2008 4:19 am

Hi,

Yeah I know the plain ol' piston valve. Performs great, in most cases.

This design probably isn't going to revolutionize anything, but who knows, it could be useful if one just wants the chamber and the barrel to be in-line, and without burst disks. Or, to experimentally get an idea (uh-oh, I guess I won the honor of having to perform the experiment some day!) of the pressure cost of the usual 90 degree bend in pneumatic gun valves.

There is some pressure/friction balancing to do all right. Fortunately, the friction of the gate plate on the barrel end should be proportional to the pressure, so one adjustment *should* fit all pressures.

There's another idea of course: The trap door valve :D This could actually be a little cool: It can be designed to open at any desired pilot chamber pressure. For example, at 1/10 of the chamber pressure.

Just exactly how to get the hinge bolt through the tee without overstressing it is another story....

Regards
Soren
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Unread postAuthor: psycix » Mon May 19, 2008 5:19 am

That popped into my mind when reading about the first valve in this topic.
Its not a bad idea. The valve will have good flow.
It just has a somewhat slow opening time.
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Unread postAuthor: dongfang » Mon May 19, 2008 5:44 am

Hi,

It just has a somewhat slow opening time


Well, a little clever design could help:

- Calculate it so that the piston will only have to move a short distance (=less acceleration needed for a particular time) to open the door fully

- Position the connecting rod on the door (relative to the door hinge) so that the torque arm will be extend at the beginning of the opening. Later, when it is already opening fast, the torque arm may be shortened again without (significant) loss of performance.

And, oops, I forgot an equaliuzation hole or valve on the drawing.

Regards
Soren
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