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Most Efficient 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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Is this more efficient than any traditionally air-piloted piston valve?

Yes, if tuned properly
4
100%
No, air-pilots would be faster
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Most Efficient Piston Valve?

Unread postAuthor: sv490665 » Tue Feb 17, 2009 6:27 pm

:idea: THEORY: I thought of this design for a piston valve, then searched around to see if anyone has done something quite like this and I didn't find anything, but maybe someone's already thought of this? Anyways, I was thinking, in theory, that this design of valve would open faster than a pilot valved one because in my design there would be only atmospheric pressure on the backside of the piston that would rush out of the "air vent holes", so when fired, the piston would slam open from the chamber pressure, like normal piston valves, but there would be alot less air pressure on the backside of the piston (where a pilot volume traditionally is) that needs to vent out, thus creating high pressure on only one side of the piston and, in effect, letting it open faster.
Reffering to the picture, the guide rod and return spring, however, would create some weight for the piston to have to deal with while it is opening, so i suggest lightweight material for the guide rod, aluminum tubing maybe. Also the proper return and catch springs for the piston would have to be figured out based on the pressure you wanted to use with this valve. BTW, the picture doesn't show this but i was planning on using epoxy or something strong to hold the springs down to the endcap so they stay in place. Also, the return spring for the release pin pushes the release pin back up to catch the end of the guide rod (when it returns to closed position) when you release your squeeze on the trigger. This allows for semi-automatic possibilities if you have flow regulated air coming into the chamber or something similar. Check it out and let me know what you think, any questions, comments, faults you see?
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Unread postAuthor: Sticky_Tape » Tue Feb 17, 2009 6:51 pm

JSR has done somthing similar but it was in a co-axial configuration with the sear at the rear of the chamber.
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Unread postAuthor: jackssmirkingrevenge » Tue Feb 17, 2009 7:28 pm

As mentioned above, this was my take on the idea.

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Unread postAuthor: sv490665 » Tue Feb 17, 2009 11:51 pm

I'm curious about performance on my valve though. I'd like to see what more people think about this design in comparison to the performance of an air piloted piston valve. One big thing I like about this sear triggered valve is that it is efficient on air and does not waste air for a pilot volume. I like JSR's design if you're making a coaxial configuration, but I am planning my specific configuration in the picture for a future project. One small thing on Jack's is looking at the way that sear is set up, when you pull the trigger it would go more down rather than sideways and up like a real trigger should feel; a small and easily fixed detail though. My main question is, does this piston open faster than an air piloted piston? Please vote and/or comment.
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 18, 2009 12:55 am

sv490665 wrote:My main question is, does this piston open faster than an air piloted piston?


Most definitely, we've all seen what a difference pilot valves make and this is the best possible one, so the performance benefits will certainly be noticed.

One small thing on Jack's is looking at the way that sear is set up, when you pull the trigger it would go more down rather than sideways and up like a real trigger should feel; a small and easily fixed detail though.


Good point, though in practice the movement was so small that it's actually quite comfortable to fire. One definite issue with that design is that the sear has to push the piston in a little before releasing, the pivot is on the wrong side (I was a 16 year old n00b at the time, ah well) - this makes it somewhat harder to pull the trigger.
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Unread postAuthor: sv490665 » Wed Feb 18, 2009 2:17 am

jackssmirkingrevenge wrote:Most definitely, we've all seen what a difference pilot valves make and this is the best possible one, so the performance benefits will certainly be noticed.


So what are you saying? Which is the best possible one? Traditional air piloted piston? or piston being released with a sear like mine? Sorry, i couldn't quite tell which way you were leaning.
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Last edited by sv490665 on Wed Feb 18, 2009 2:37 am, edited 1 time in total.
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Unread postAuthor: Gippeto » Wed Feb 18, 2009 2:33 am

You asked for opinions, so you'll get one. :)

I'll use my copper gun as the example. Keep in mind, my chambers are small compared to what most people use. My B:C is ~0.8 to 1.

The chamber volume is ~7.23 cu.in.

The pilot volume is ~0.28 cu.in.

The amount of air being wasted is ~3.7% of the total. In my opinion, it's not enough to be of consequence.

In the case of the more popular B:C of say 2:1, the percentage of loss is reduced.

Is trying to save that few percent worth it? That's up to the individual. :)
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Unread postAuthor: sv490665 » Wed Feb 18, 2009 2:42 am

Gippeto wrote:You asked for opinions, so you'll get one. :)
I'll use my copper gun as the example. Keep in mind, my chambers are small compared to what most people use. My B:C is ~0.8 to 1...

...The amount of air being wasted is ~3.7% of the total. In my opinion, it's not enough to be of consequence.
In the case of the more popular B:C of say 2:1, the percentage of loss is reduced.
Is trying to save that few percent worth it? That's up to the individual. :)


Ok so maybe it doesn't save all that much air, that's fine, but it is a nice small perk to have when your gun has onboard gas supply in small canisters such as co2. Most important question to me is if my piston opens faster than that of an air piloted piston.
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Unread postAuthor: john bunsenburner » Wed Feb 18, 2009 2:48 am

Gip, is it just me or did you get you C:B(B:C) ratios wrong? Because if the barrel has twice the volume of the chamber something must be wrong...Or am i totally of?

Sv: how about you just build both and find out?
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Unread postAuthor: Gippeto » Wed Feb 18, 2009 3:03 am

Got me. I goofed up, and mixed my B's and C's, but hey...it's closing on one in the morning here.

Barrel (8.95 cu.in.) to Chamber (7.23 cu.in.) = 1.24 :1

Chamber to Barrel would be ~0.8:1

I'll leave the other post un-edited so this all makes sense.

Good catch. :)
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Unread postAuthor: john bunsenburner » Wed Feb 18, 2009 3:32 am

Your welcome, i was just really confused haha. :D
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 18, 2009 9:26 am

Gippeto wrote:Is trying to save that few percent worth it? That's up to the individual. :)


It's not about wasted air, it's about valve opening time - and removing the pilot chamber completely means that your piston is going to open much faster than if you had the best pilot valve and minimal pilot volume.

Which is the best possible one? Traditional air piloted piston? or piston being released with a sear like mine?


The air piloted piston can never be as good as a sear released one, simple as that.
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Unread postAuthor: john bunsenburner » Wed Feb 18, 2009 9:52 am

I am starting to get an idea... maybe i could build an air powered semi auto hammer valve gun....
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Unread postAuthor: sniper hero » Wed Feb 18, 2009 10:08 am

sounds great and you get the idea of pulling a real trigger.
build it :D
is it nessesary to to have 2 springs or could these be combined?
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Unread postAuthor: btrettel » Wed Feb 18, 2009 10:59 am

Valves like this where the pilot volume is eliminated should generally open at about the same speed if each are well tuned. If the practical minimum pilot volume is pretty big, this'll open faster. If the practical minimum pilot volume is a substantial portion of the gas chamber's volume, the saved air could be very substantial.

I've been looking at valves without any pilot exhaust and with small guns (like what I'm interested in) they can improve energy efficiency 20% or more. That's not saying that they necessary will--just that they can.

If the pilot volume is negligibly small compared against the gas chamber volume, I wouldn't worry too much about it.
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