Author Topic: Airgun valves and using a cam to open them  (Read 260 times)

steveoh

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Airgun valves and using a cam to open them
« on: October 12, 2018, 09:13:32 AM »
Bob,
Had an idea this morning about opening a valve on an airgun using a cam instead of a hammer. Are there any airguns using such a mechanism? Seems like varying the grind of a cam would allow a whole bunch of variables being controlled including how far the valve opens, the duration etc.

I realize that such a mechanism might add just a tad bit more complexity. And yeah it's on my mind since I recently got an Efficiency/Tow cam installed in my Cummins surrounded by a Dodge.

Thanks!

Steve


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Alan

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Re: Airgun valves and using a cam to open them
« Reply #1 on: October 12, 2018, 10:00:48 AM »
Complex! Yes, I'm sure, but like valve lift in a vehicle, it isn't difficult—only the base design is.

For me, I wonder why a rotary hammer hasn't been tried (perhaps it has). A very simple ratchet design would eliminate hammer bounce without a bunch of extra spring, guides, etc.
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rsterne

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Re: Airgun valves and using a cam to open them
« Reply #2 on: October 12, 2018, 01:22:28 PM »
Lloyd and I spent a while working on a design for a valve driven by a cam, which was driven by a torsion spring.... We had what we thought was a "working" design but never proceeded because of the complexity required.... This idea is nothing new, in fact the Girardoni used a similar mechanism.... combined with a true (rotary) hammer.... rather than a sliding striker....

The drawback, of course, is that any type of "constant dwell" valve, however well it might work in a regulated PCP, would produce a Korean cliff shot string in an unregulated PCP.... If the lift and dwell are constant, the mass of air (and hence the potential FPE) that can pass through the valve per shot is proportional to the pressure....

The Mac1 USFT rifle, and its derivatives, use a rotary hammer (thumb cocked)…. although I think it strikes a conventional (self-regulating) valve.... That type of design should, indeed, lend itself to less hammer bounce, with proper configuration....

Our conventional "strike-open" valve can self-regulate over quite a wide range of pressures, producing the "bell-curve" in unregulated PCPs.... Timed valves don't do that, unless you can vary the dwell electronically (or through some complex mechanical system)....

Bob
« Last Edit: October 12, 2018, 01:24:07 PM by rsterne »
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steveoh

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Re: Airgun valves and using a cam to open them
« Reply #3 on: October 12, 2018, 04:00:55 PM »
Excellent Bob. I figured that my idea twert a new one. Pretty interesting stuff me thinks.
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sixshootertexan

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Re: Airgun valves and using a cam to open them
« Reply #4 on: October 12, 2018, 07:37:35 PM »
I've been kicking around in my head a fulcrum setup for a AirForce type valve. Having the hammer slide forward instead of rearward like AF's does. This would eliminate turning the barrel down so the spring/hammer fits over it. Making the barrel stiffer. If you can move the pivot point it will take less hammer strike to open valve. I have some preliminary drawings made but time has not been on my side lately to finish them.
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