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Advanced Piston Design

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Advanced Piston Design

Unread postAuthor: Marco321 » Wed Oct 24, 2007 2:01 am

I have been thinking about pistons and came up with this idea about making them open faster.
For those who understand pistons, will know they move because of a force differential. The force is created by air pressure pushing on a surface area, the more surface area, the more force. The more force in front of the piston, the smaller the pressure differential can be behind it. Now here comes the new part... What if instead of having a flat surface at the front of the piston, why not have a cone shape. The advantage this would have would be that the cone could be specially designed to have slightly less surface area than behind the piston. What this would create slightly more force behind the piston than in front, this would then mean only a small pressure drop of about 5PSI behind the piston would actuate it. Because there would be more force behind the piston than normal, it would also increase opening speed. This, combined with minimal pilot volume should create the most efficient, fast opening piston available, possibly even on the commercial market. I believe it would even compete with something like a QEV or a diaphragm valve. Here is a diagram. its not to a perfect scale, but its pretty close.

Image

EDIT: Sorry bad diagram, wait a few mins and ill remake it

EDIT EDIT: Here is a proper diagram Image
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 24, 2007 2:06 am

It won't make a difference because even though the surface area is greater, the force is not acting backwards but at a tangent to surface of the piston, meaning the total force acting to push the piston back is identical to a conventional piston.
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Unread postAuthor: Marco321 » Wed Oct 24, 2007 2:08 am

jackssmirkingrevenge wrote:It won't make a difference because even though the surface area is greater, the force is not acting backwards but at a tangent to surface of the piston, meaning the total force acting to push the piston back is identical to a conventional piston.


Good point. Ill try think of a way to increase surface area in one direction :P
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 24, 2007 2:10 am

bigger chamber and lighter piston ;)
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Unread postAuthor: Marco321 » Wed Oct 24, 2007 2:17 am

jackssmirkingrevenge wrote:bigger chamber and lighter piston ;)


Hmm yeah, i gues so, i just saw this thread and saw the diagram of the QEV and thought about the cone shaped edge and posted my topic :P
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Re: Advanced Piston Design

Unread postAuthor: jrrdw » Wed Oct 24, 2007 5:37 am

Marco321 wrote:I have been thinking about pistons and came up with this idea about making them open faster.
For those who understand pistons, will know they move because of a force differential. The force is created by air pressure pushing on a surface area, the more surface area, the more force. The more force in front of the piston, the smaller the pressure differential can be behind it. Now here comes the new part... What if instead of having a flat surface at the front of the piston, why not have a cone shape. The advantage this would have would be that the cone could be specially designed to have slightly less surface area than behind the piston. What this would create slightly more force behind the piston than in front, this would then mean only a small pressure drop of about 5PSI behind the piston would actuate it. Because there would be more force behind the piston than normal, it would also increase opening speed. This, combined with minimal pilot volume should create the most efficient, fast opening piston available, possibly even on the commercial market. I believe it would even compete with something like a QEV or a diaphragm valve. Here is a diagram. its not to a perfect scale, but its pretty close.

Image

EDIT: Sorry bad diagram, wait a few mins and ill remake it

EDIT EDIT: Here is a proper diagram Image


Something that crossed my mind reading your description. If the piston opens with just approx. 5 lbs pressure difference, the valve opening the pilot chamber would have to be at almost equal flow, or it will act as a air brake. The faster opening time will out run the escaping air. With the cone shaped piston, it will be problem-matic, tilting from side to side binding the piston causing jamming failure.
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Re: Advanced Piston Design

Unread postAuthor: Marco321 » Wed Oct 24, 2007 5:19 pm

jrrdw wrote:Something that crossed my mind reading your description. If the piston opens with just approx. 5 lbs pressure difference, the valve opening the pilot chamber would have to be at almost equal flow, or it will act as a air brake. The faster opening time will out run the escaping air. With the cone shaped piston, it will be problem-matic, tilting from side to side binding the piston causing jamming failure.


Thats a good point

It appears JSR has the right idea of a light piston with minimal pilot volume
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Re: Advanced Piston Design

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Unread postAuthor: dapallox1 » Wed Oct 24, 2007 5:26 pm

When I first saw a piston valve, I thought this was how they were. (I don't anymore, don't worry, haha) But yes, in theory that would work, but then when you tell someone else, they always seem to point out something different. I do wonder if shaping a piston differently would effect it at all.
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Unread postAuthor: Hotwired » Wed Oct 24, 2007 5:55 pm

If you want just a small pressure difference to operate the piston use a chamber sealing valve or do this:

Image

You lower the pilot force by decreasing the area the gas is pushing on. the pilot-side area still has to be more than the chamber-side area but not much to keep it closed.
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Unread postAuthor: Marco321 » Wed Oct 24, 2007 6:27 pm

@Dapallox1
I think it depends how you shape it.

@Hotwired
Thats an interesting idea
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Unread postAuthor: HaiThar » Wed Oct 24, 2007 7:05 pm

jackssmirkingrevenge wrote:It won't make a difference because even though the surface area is greater, the force is not acting backwards but at a tangent to surface of the piston, meaning the total force acting to push the piston back is identical to a conventional piston.


Are you sure that the tangent and force acting on it are directly correlational? If so, pretty cool, I didn't realize it... :P

But anyway, cool idea. What if you enlarged the chamber, so that the force was not just acting on the front of the piston, but the sides as well? Would this help?
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Unread postAuthor: clide » Wed Oct 24, 2007 9:44 pm

As others have pointed out the original idea won't work, but even if it did, that is not a desirable trait of a piston valve. Although it will open fast in terms of time from pulling the trigger to the valve opening, the actual opening of the valve will be slower because there is more pressure behind the piston to restrict opening movement. It will also be very prone to bouncing and not opening completely.
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 24, 2007 11:12 pm

It will also be very prone to bouncing and not opening completely.


Unfortunately piston bounce is a difficult phenomenon to measure - I was startled with the results of my 6mm burst disk launcher compared to the HVBB piston launcher with similar barrel length and double the chamber size. The latter (you might remember from spudtech) had a consistent anomaly of proportionally lower velocities with lighter projectiles, something which the burst disk wasn't prone to so it must have been the piston valve.
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Unread postAuthor: clide » Thu Oct 25, 2007 1:03 am

I do remember that gun. I have recently seen evidence that suggests that GGDT is fairly accurate in predicting if the valve will bounce or not (although I'm not sure about the performance accuracy when the valve bounces). I'd be interested to see what it says about your particular valve, for best results be as accurate as possible with all the valve parameters.
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