Likely the hammer is bouncing off the back of the valve as you increase the hammer spring preload.... I have seen that on some guns.... If it hits the back of the valve hard enough and bounces off, the dwell gets shorter instead of longer.... Bob
No, an unregulated air rifles does not have a plenum. I suppose you could think of the reservoir as a plenum but that muddies the waters.
Quote from: rsterne on August 24, 2019, 06:00:29 PMLikely the hammer is bouncing off the back of the valve as you increase the hammer spring preload.... I have seen that on some guns.... If it hits the back of the valve hard enough and bounces off, the dwell gets shorter instead of longer.... BobHmm - possible. Given there is hammer spring preload, the dynamic tension of the hammer spring to valve spring is less than the recoiling of the hammer off the valve body, and that latter force overcomes the hammer spring preload driving the hammer back, resulting in less dwell.
Quote from: CraigH on August 25, 2019, 09:11:50 AMQuote from: rsterne on August 24, 2019, 06:00:29 PMLikely the hammer is bouncing off the back of the valve as you increase the hammer spring preload.... I have seen that on some guns.... If it hits the back of the valve hard enough and bounces off, the dwell gets shorter instead of longer.... BobHmm - possible. Given there is hammer spring preload, the dynamic tension of the hammer spring to valve spring is less than the recoiling of the hammer off the valve body, and that latter force overcomes the hammer spring preload driving the hammer back, resulting in less dwell. But dont know if thats likely happeing on the Crown when adding a tiny more tension on the spring, remember the plenum has 145 bar, so hit that valvestema so hard so the hammer strikes against the valvebody, hmmmm?If thats the case, then FX surely did calculate everything exactly right with hammerspring, hammerweight, distance of travel and everything to be exactly 100% max speed without losing air when the hammerwheel adjuster is max and the setstrew has no play... not possible
What Bob described is correct, it is a well understood behavior of FX airguns that results from having the valve limiter set too aggressively along with striking the valve too hard. This topic pops up frequently on airgunnation.The nature of how it works is a little different though. It does not drive the stem against the back of the valve body. Rather, the valve limiter feature has a rubber ball that stops the valve from exceeding a particular amount of lift.
Quote from: sebbe666 on August 25, 2019, 10:29:54 AMQuote from: CraigH on August 25, 2019, 09:11:50 AMQuote from: rsterne on August 24, 2019, 06:00:29 PMLikely the hammer is bouncing off the back of the valve as you increase the hammer spring preload.... I have seen that on some guns.... If it hits the back of the valve hard enough and bounces off, the dwell gets shorter instead of longer.... BobHmm - possible. Given there is hammer spring preload, the dynamic tension of the hammer spring to valve spring is less than the recoiling of the hammer off the valve body, and that latter force overcomes the hammer spring preload driving the hammer back, resulting in less dwell. But dont know if thats likely happeing on the Crown when adding a tiny more tension on the spring, remember the plenum has 145 bar, so hit that valvestema so hard so the hammer strikes against the valvebody, hmmmm?If thats the case, then FX surely did calculate everything exactly right with hammerspring, hammerweight, distance of travel and everything to be exactly 100% max speed without losing air when the hammerwheel adjuster is max and the setstrew has no play... not possibleIve posed this question over at AGN not to long ago because i was curious also. Got a bunch of guesstimates, but nothing solid. No way of really knowing. Typical fx valve pin.The narrow part of the pin is where the air flows to the transfer port. My guess is if you start over driving it with more hammer its going to start blocking the air flow. Or, like Bob said. Possibly bouncing the pin off the back wall shortening the dwell. No way of knowing for sure.
Quote from: RDB on August 25, 2019, 11:18:24 AMQuote from: sebbe666 on August 25, 2019, 10:29:54 AMQuote from: CraigH on August 25, 2019, 09:11:50 AMQuote from: rsterne on August 24, 2019, 06:00:29 PMLikely the hammer is bouncing off the back of the valve as you increase the hammer spring preload.... I have seen that on some guns.... If it hits the back of the valve hard enough and bounces off, the dwell gets shorter instead of longer.... BobHmm - possible. Given there is hammer spring preload, the dynamic tension of the hammer spring to valve spring is less than the recoiling of the hammer off the valve body, and that latter force overcomes the hammer spring preload driving the hammer back, resulting in less dwell. But dont know if thats likely happeing on the Crown when adding a tiny more tension on the spring, remember the plenum has 145 bar, so hit that valvestema so hard so the hammer strikes against the valvebody, hmmmm?If thats the case, then FX surely did calculate everything exactly right with hammerspring, hammerweight, distance of travel and everything to be exactly 100% max speed without losing air when the hammerwheel adjuster is max and the setstrew has no play... not possibleIve posed this question over at AGN not to long ago because i was curious also. Got a bunch of guesstimates, but nothing solid. No way of really knowing. Typical fx valve pin.The narrow part of the pin is where the air flows to the transfer port. My guess is if you start over driving it with more hammer its going to start blocking the air flow. Or, like Bob said. Possibly bouncing the pin off the back wall shortening the dwell. No way of knowing for sure.cant see anything on that valvesteam limiting anything with airflow to the breach if hit 1mm to "far" ?
Bob's point was that there is a limit to the hammer energy that can be handled all through the impact on the valve stem - at some point the hammer has so much energy that it simply provides a max lift to the stem and then bottoms out on the body of the valve and immediately bounces back up. And at this point the valve has less dwell than it had with a little less hammer strike, resulting in a shorter duration of the cycle with no significant change in valve lift . . . thus less air passes, even with more and more hammer force.
Can't even come up with a reasonable theory that doesn't envolve either air flow or rebound/bounce. We've already talked about rebound/bounce.Looking at that tapered/rebated pin,could be possible to dive it far enough in that not all of the rebated section is in line with the transfer port?
Im a little confused on something I was hoping someone could clear up? On my regulated bantam magnum, the plenum volume from what I understand is about 2.5cc. At 150 bar I can make 60fpe. Yet all I read is how it needs .5-1cc per fpe to make that energy yet Im not even remotely close. What am I not understanding here?
Haha Im sorry guys its closer to 16cc. 30 yrs in machining and not much metric time for me!
Not 2.5 cc.... Reply # 15....QuoteHaha Im sorry guys its closer to 16cc. 30 yrs in machining and not much metric time for me! then add the valve volume to that as well....Bob
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