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Enhancing a Piston Valve

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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Unread postAuthor: AngryChauncey » Wed Oct 28, 2009 11:05 pm

Ragnarok wrote:I've detailed my thoughts on piston valve opening times already.

Any decent piston valve already opens fast enough (a couple of milliseconds) that even being able to halve the opening time will only yield a few more feet per second.

For those that like data, figures calculated for 3vo with various valve speeds can be found at the link above. In its case, the improvement of a valve that opens instantly is only 1% more energy than a 4ms valve - and in reality, its valve will open in around about 1 ms. Any further effort to further lower that can't even offer me another whole joule on the muzzle energy.

If you want to find ways to improve piston valve performance, then don't focus on valve opening time, it's good enough already. Focus on bringing up valve flow.


This is right on. Even if you did spend enough time designing a sealing face that is only the sealing face so it doesn't way hardly anything, I don't think you would ever notice the difference. One thing that I could improve on my piston (others as well possibly) is the opening distance and the pilot volume. This wood greatly improve the efficiency (correct me if I'm wrong Ragnarok) of the valve a lot.
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Unread postAuthor: Technician1002 » Wed Oct 28, 2009 11:52 pm

AngryChauncey wrote:
Ragnarok wrote:I've detailed my thoughts on piston valve opening times already.

Any decent piston valve already opens fast enough (a couple of milliseconds) that even being able to halve the opening time will only yield a few more feet per second.

For those that like data, figures calculated for 3vo with various valve speeds can be found at the link above. In its case, the improvement of a valve that opens instantly is only 1% more energy than a 4ms valve - and in reality, its valve will open in around about 1 ms. Any further effort to further lower that can't even offer me another whole joule on the muzzle energy.

If you want to find ways to improve piston valve performance, then don't focus on valve opening time, it's good enough already. Focus on bringing up valve flow.


This is right on. Even if you did spend enough time designing a sealing face that is only the sealing face so it doesn't way hardly anything, I don't think you would ever notice the difference. One thing that I could improve on my piston (others as well possibly) is the opening distance and the pilot volume. This wood greatly improve the efficiency (correct me if I'm wrong Ragnarok) of the valve a lot.


The reference cited is like finding the energy to lift a ? up 5 feet. Speeds are given and percentages on efficiencies, but the pressure and mass are missing from the summary. Higher pressure, shorter barrels, and lower mass projectiles provide different performance graphs for each.

As an example of where the energy does vary a lot vs opening speed is my marshmallow launcher. Only a fast valve will deliver the energy to dent a car door with a marshmallow at moderate pressure. The conclusion is too generalized. Heavy projectiles that sit for a while can wait for a slow valve. Marshmallows don't wait for a slow valve to open completely.
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Unread postAuthor: AngryChauncey » Thu Oct 29, 2009 12:00 am

The reference cited is like finding the energy to lift a ? up 5 feet

This makes absolutely no sense.
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Unread postAuthor: Technician1002 » Thu Oct 29, 2009 12:16 am

AngryChauncey wrote:
The reference cited is like finding the energy to lift a ? up 5 feet

This makes absolutely no sense.


It was a thinly veiled attempt to point out the missing data. The energy variation is dependent on the other parameters. Maybe it would have made more sense to find the Foot Pound Seconds of energy required to lift a full bucket. Unstated is the size of the bucket, the height to lift it, and the mass of the contents.

OK sorry. The variation of power only on valve times was given. Those values are only good with a known mass, pressure and barrel length.

Changing to a heavier or ligher projectile will change the values stated.

Changing the operating pressure will change the values given. A 20 PSI cannon can use a slow valve. A 600 PSI airsoft pellet gun with a 18 inch barrel will be about useless with a valve that takes 4 ms to open. The power change from 0ms to 4 ms valve time is huge on a plastic pellet.
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Unread postAuthor: AngryChauncey » Thu Oct 29, 2009 12:24 am

The power change from 0ms to 4 ms valve time is huge on a plastic pellet.




Yeah it is :o . Sorry I didn't specify but i meant you wouldn't notice much of a difference on a big projectile like a potato. I need to be more specific on these forums :x
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