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piston valve Pnuematic vs Advanced combustion.

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piston valve Pnuematic vs Advanced combustion.

Unread postAuthor: jmeyer1022 » Sun Nov 23, 2008 11:39 pm

I've built simple versions of Pneumatic and a moderate combustion (fan and propane, terrible ignition and sloppy set up.)

I'm wondering which one gives more power, So far I'm looking at combustion mainly because its transportable; but I often just set up lots of boards objects on stands in front of my shed and unload.

So which one houses more power? I've seen both in action before and i'm still unsure I know combustion will be alot noiser but my neighbors are already use to it.
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Unread postAuthor: jook13 » Sun Nov 23, 2008 11:42 pm

A good piston valve will out perform any combustion of the same size. At least thats the idea that I get. Still, a well made metered propane cannon will be impressive, especially at a large size.
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Unread postAuthor: jmeyer1022 » Sun Nov 23, 2008 11:46 pm

jook13 wrote:A good piston valve will out perform any combustion of the same size. At least thats the idea that I get. Still, a well made metered propane cannon will be impressive, especially at a large size.


Not sure what you consider large, I plan on keeping it at 4"x24" barrel for combustion and if I do a pneumatic piston this size.

This is my last gun I'm making for a while so help me out =).
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 24, 2008 1:03 am

A combustion will only give you so much pressure, but it will do so without the normal opening time and flow restriction of a pneumatic valve.

With a pneumatic on the other hand, you decide how much air and at what pressure you put it - so given a good enough valve, the power potential is much greater for a similarly sized pneumatic.

That said, a 4" piston valved launcher is going to represent quite an investment in material terms, were you planning on making a coaxial launcher?
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Unread postAuthor: jmeyer1022 » Mon Nov 24, 2008 1:10 am

As I said I'd go 4" chamber only for combustion, the pneumatic piston, If I chose that path I'm not sure how big I'll go.
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Unread postAuthor: starman » Mon Nov 24, 2008 4:22 am

What are you going to shoot ammo-wise with this "large" gun? Where are you going to shoot it?

Large pneumatics will always have to be co-located with an air compressor which will also required AC power. Combustions are ready to travel where ever you want.

Actual "power" really depends on your design and implementation of the cannon. Either design can be made more powerful if one is optimized and the other isn't. I would put a well designed 1X combustion with a burst disk up against a similar chamber/barrel sized piston pneumatic up to 120 psi or so any day of the week. You aren't going to get pressures much higher than that from commercial air compressors anyway.

However, I am a "little biased" toward combustions so figure that into your calc... 8)
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Unread postAuthor: john bunsenburner » Mon Nov 24, 2008 4:46 am

How about using a hybrid? If you do it well it will be better than both pneumatic and combustion, because it uses the attributes of both gun typed to make a even better one...
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Unread postAuthor: psycix » Mon Nov 24, 2008 4:23 pm

Both have their pro's and cons.
Most of the times combustion is more portable, and pneumatic more powerful, especially if the pressure is raised up.

Combustion may be cheaper and easier, as you wont need a valve.
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Unread postAuthor: jitup » Mon Nov 24, 2008 7:13 pm

I would build the combustion if you are going to be taking is places you may not have power or if you do not have a HPA compressor (or a fridge compressor, or CO2 rig)

Honestly, I would go with a CO2 powered large cannon, unless you have a budget. The combustion, if done correctly will be impressive as well.

If you want al out power I agree with John, go for the hybrid
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Unread postAuthor: starman » Mon Nov 24, 2008 7:18 pm

john bunsenburner wrote:How about using a hybrid?


A hybrid still requires a source of compressed air or O2 or a way to compress it on the spot. Not insurmountable of course, just a good bit more complicated...even more so with a large cannon.
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Unread postAuthor: SpudBlaster15 » Tue Nov 25, 2008 1:06 am

A properly metered propane combustion launcher will outperform a similarly sized pneumatic charged to average shop compressor pressures.
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Unread postAuthor: starman » Tue Nov 25, 2008 1:22 am

SpudBlaster15 wrote:A properly metered propane combustion launcher will outperform a similarly sized pneumatic charged to average shop compressor pressures.


Word on that SB!! That's been my experience as well.
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Unread postAuthor: MrCrowley » Tue Nov 25, 2008 2:14 am

SpudBlaster15 wrote:A properly metered propane combustion launcher will outperform a similarly sized pneumatic charged to average shop compressor pressures.

Let's say the combustion has a 1.5" barrel, so that can be the port on the piston valve too. Shop compressors, max at 125psi (yes I know you can get ones that go higher, but they're not really 'shop compressors'), same size chamber (diameter and length) and barrel length...

I would say it's pretty equal, combustions have the footup on faster gases (because they're hotter, right?) and no flow restriction, pneumatic has the lead for pressure by a good... 30psi?

I'm a pneumatic guy myself, if you want to take this cannon out and about, like the others say, go combustion. Combustion is probably better to show off to your friends as well.

Pneumatics are good for being used at home (if they're too large for a bike pump) and as jsr put it "the power potential is much greater for a similarly sized pneumatic".

A piston valved pneumatic requires probably the same amount of skill as an advanced combustion. I just see more potential in pneumatics, so I favour with them.

They'd probably cost the same too build also.
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Unread postAuthor: Ragnarok » Tue Nov 25, 2008 8:08 am

Here's my general advice:
- If you want to build a small cannon, go pneumatic.
- Mid size cannon, either. It would be good to have a compressor for pneumatics of this size.
- Big cannon - it's far easier to go combustion, because it would be a lot of work to create the valves, and a lot of time to fill. Most big pneumatics get used at surprisingly low pressures anyway.

Want it portable? Go combustion.
Want it to really throw it's weight? Pneumatic, and really crank up the pressure.

HEAL, despite being the smallest of the cannons I built with intent of power, is by far the most powerful, especially with the more recent tests with a bit more pressure again...
It kicks seven shades of snot out of my butane fueled ABS combustion for power, (which I should note has a 1.5" barrel that's 5 foot long, not a 0.8" barrel that's less than 4' long). Okay, the ABS cannon's not precisely metered, but it has a chamber fan, and it's one of my oldest cannons, so I've used it more than enough times to get the fuelling down pretty close.

Okay, not the average pneumatic, but it proves that pneumatic can be far more powerful for a given size...
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Unread postAuthor: jimmy101 » Tue Nov 25, 2008 11:22 am

You might consider getting both HGDT and GGDT and fiddling around with various designs. Both programs are excellent, and if you can correctly model the pneumatic's valve both programs will give you a very good idea of the relative performance.

GGDT will give you a good idea of how much better say a piston valve will perform than a sprinkler valve.

HGDT will give you an idea of how much better the combustion will perform with a fan and/or multiple sparks.
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