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Spring-loaded chambers

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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Spring-loaded chambers

Unread postAuthor: PVC Arsenal 17 » Fri Aug 19, 2011 7:04 pm

After reading this Nerf thread I've been curious about the possible advantages of spring-loaded or even latex bladder air chambers.

In short, the OP claims that extra power results from using the full chamber volume rather than just what escapes when the chamber pressure drops down to atmospheric pressure as a result of simply opening it.

It seems rational enough, but I'd like to hear others' thoughts on the matter being that I'm not yet educated in this area.

If there is a lot to gain, I'll be very interested. Some premade chamber alternatives could be double acting cylinders (variable air spring) and water hammer arresters.
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Unread postAuthor: Moonbogg » Fri Aug 19, 2011 8:47 pm

I think any power gained from a spring could be made up by just increasing chamber pressure a little. If the spring was absurdly powerful, like in a spring piston air gun, then you may have something there. Just my opinion. Oh, by the way, I have NEVER built a pneumatic cannon in my life :lol:
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Unread postAuthor: Gippeto » Fri Aug 19, 2011 9:48 pm

There are a couple examples I can readily think of that make use of the principle...it's nothing new.

The now defunct Ana arms Quigley rifle for one, http://www.americanairgunhunter.com/quigley.html

and the Webley-Venom Paradigm..

http://www.youtube.com/watch?v=pJGKkL7vxy4

The concept maintains pressure at the valve for an increased duration.

It does work.
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 19, 2011 11:45 pm

I think the idea makes sense if you have to make a compact package and have a size restriction, otherwise simply use a bigger chamber or use a higher pressure tank that's regged down.
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Unread postAuthor: saefroch » Sat Aug 20, 2011 12:13 am

Here's how I see it: Compute the period for your spring. Find the time until the projectile has left the barrel. If spring's period > time for projectile to exit barrel, spring is pointless.

Maybe I have an oversimplified view of this concept, but hey... I like it that way :D.
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Unread postAuthor: PVC Arsenal 17 » Sat Aug 20, 2011 11:18 pm

What a shame the Paradigm won't make it to market.

I got a water hammer arrester today but with most of my components in storage, the most I could do was pressure test it (400psi) and release the air via schrader valve. Judging by the sound - sustained "woosh" rather than tapering off - the piston seems to be forcing the air out with more vigor than usual. Further tests to come, but this looks promising. If the arrester doesn't destroy itself from the slamming forces certain to happen with a QEV, I think I can have a super efficient low volume cannon.
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Unread postAuthor: Hotwired » Sat Aug 20, 2011 11:34 pm

I'm sure the matter of the weight and space of spring loading chambers came up last time this was discussed.

Especially with significant size chambers not the millilitre volumes in a single stroke air rifle.

In addition do you not get a much more space efficient result by using a larger precharged chamber and a hammer valve?



Hybrids and combustions on the other hand there's an extra use for sprung chambers in that they will automatically clear the chamber after firing. The strength of the spring wouldn't even matter much for that, just enough to sweep out the spent gases.
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Unread postAuthor: PVC Arsenal 17 » Tue Apr 10, 2012 2:37 pm

I thought I'd dig this one up since I have a new take on the idea.

Forget the spring, instead put a lightweight piston in the air chamber to divide it into two sections. As before, the chamber would be filled and dumped via a valve on one side. A small orifice or even a check valve would be incorporated in the piston so that when pressure is applied on the valve side, air can pass through the piston to the other side. A stopper would be installed somewhere along the chamber to stop the piston from sliding to the other end during filling. This stopper establishes the point at which the piston divides the chamber.

When fired, air dumps from the valve side but pressure remains on the other side of the piston because of the check valve/restriction. This pressure then pushes the piston to the valve end thus completely expelling the volume as the spring did. The volume behind the piston, however, remains there or perhaps only a tiny fraction of it is lost. When filled again, the piston returns to the initial position assuming that the flow rate of the supply far exceeds the flow rate of the piston's check valve/orifice.

Essentially this would act as an air spring, but one that would not require precise construction. The pressure equalization ensures that the spring is always properly pressurized and there is no need to worry about leakage. The piston would not even need to perfectly isolate the two portions of the chamber. It's possible that o-rings would not even be necessary.

Additionally you can set the location of the stopper in order to obtain the ideal spring:firing volume ratio. (...I'm curious what that may be...)

TL;DR version: Replace the metal spring with an adjustable air spring whose pressure is maintained by the gun itself, thus permitting some degree of shoddy construction.


Why do I care about doing this? I'm hoping to find a way to get as much power as I can while consuming the least volume possible.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 10, 2012 3:08 pm

I'm sure that it would lead to an increase in power, but personally I doubt it would vary by a significant percentage.
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Unread postAuthor: PVC Arsenal 17 » Tue Apr 10, 2012 4:05 pm

That is what I intend to find out! Once I get a chronograph, I will build a rig to test the concept with different spring:chamber ratios across a range of pressures and compare it to a conventional pneumatic simply by locking the piston in place.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 10, 2012 4:07 pm

PVC Arsenal 17 wrote:simply by locking the piston in place.


No need, if it's an air spring just open the space behind it to the atmosphere ;)
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Unread postAuthor: Major Collins » Wed Apr 11, 2012 1:39 am

Well i wonder why you didn't mention it Jack but he did make an "air spring" and the concept does work ... http://www.spudfiles.com/forums/custom- ... 17142.html
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Unread postAuthor: Hotwired » Wed Apr 11, 2012 8:25 am

Alternatively.

You simply don't exhaust the full capacity of the chamber when you fire.

I mean this whole thing is about "squeezing the last bit of air out" by adding more weight in various ways to do so.

So think of the volume of air you want expelled as one thing.

Now consider the (still compressed) air left behind as another thing. The "spring" if you will.



Off the top of my head I am aware of two mechanisms to release some of the air in a chamber.

A hammer valve and a dump valve with a partially vented pilot.



That is simpler and more effective than having a mass dampening the flow in the chamber and then having to fiddle with pressures either side.
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Unread postAuthor: PVC Arsenal 17 » Wed Apr 11, 2012 9:26 pm

Hotwired: Mind=blown. Somehow that never crossed my mind.

I think I'll rig up something like Gun Freak's Project and use a solenoid to actuate the valve. At least it gives me another excuse to use a μController and a trim pot to adjust valve opening time.

Case closed here, I'd say. Though I might still make the air-spring just out of curiosity.
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