Yes, turning the TH changes velocity. But WHY exactly???
Up untill recently, i tought i was 100% clear on this. If i close the opening on my TH, velocity will go down. I turn the TH open, and up goes the speed.
But now i realize i have never truly understand the “mecanics” of WHY this happens!
My first theory was, that when the hammer hits the breech, and it in turns “presses” on the TH, the TH would go back till it hit the valve face, then the energy from the hammer would dissipate, and the valve would be shut closed again, therefore a TH with a wider opening (lets say 0.080″), would take longer to hit the face valve (longer distance to travel till hitting the valve face), resulting in the valve remaining open for longer, and more air escaping it.
Likewise, a TH with a smaller distance to the valve face (say 0.040) would have to travel LESS till hitting the valve face, remaining open for LESS time, and less air escaping it.
But now that i think of it, the TH doesnt really hit the valve face! and its actually an un-desirable conditon for it to do so (because of POI shift when it happens). So, if it doesnt work this way…
¿Exactly why does a TH of 0.040 produces less velocity that one wiht 0.080?
¿is it because the hammer has a longer run and so it impacts with more force?
or
¿is it because it lasts open longer? if so ¿why does it lasts longer open, if the TH doesnt hit the valve face?
I really like knowing how things work, so i Would really appreciate if someone could explain this to me, or point me in the right direction of what to read.
thanks!
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Viewing 11 replies - 1 through 11 (of 11 total)
Another thing to realize is if the top-hat is open to much the velocity will also start dropping, for you tuners who like changing hammers and springs.
I just went through this exercise and arrived at 0.084 and 0.087 for my two bottles to have similar penetration (phone book) after five shots with a starting pressure of 2500psi fill.
The loud bottle is a little quieter with 0.084 down from a factory 0.09x. The quieter bottle with a loose fitting breech is much better at 0.087 up from factory 0.076.
My goal was to have similar starting performance at the same gun PW setting. I know there will be variation in air usage and shot string but all I care about is hitting a 1.5″ target at 30 yards for about 50 shots with the same pellet and PW setting. Penetration should be about the same at the end of my string.
If you set the tophat so the hammer is not loaded by the spring when the hammer is in contact with the top hat then the spring will have no effect on the tophat a this point…
If the hammer spring is not putting a load on the hammer as it contacts the tophat, friction and other things influencing the hammer will begin to rob the energy that was imparted to it by the spring and thus reducing it’s possible power to give to the tophat/valve…
😕
Very interesting, so basically your tehory is that a TH set at 0.090, gets more hammer (and spring) force applied to it than one set at 0.040, because the hammer has more spring force when it hits it. right?
It makes sense, i guess it would be the same as adjusting spring preload just like you do with the PW, except on the other side.
If the hammer spring is long enough for the load of the spring to effect the hammer as it touches the tophat. Projecting the tophat further from the valve face will increase the amount of load against the hammer as the hammer contacts the tophat…
If you set the tophat so the hammer is not loaded by the spring when the hammer is in contact with the top hat then the spring will have no effect on the tophat a this point…
If the hammer spring is not putting a load on the hammer as it contacts the tophat, friction and other things influencing the hammer will begin to rob the energy that was imparted to it by the spring and thus reducing it’s possible power to give to the tophat/valve…
😕
Thanks for your replies,
Im sorry, i guess i dint properly expressed what i meant. Yes, i understand about longer stroke = more air & shorter stroke = less air.
What i was curious about is WHY, why does a TH at 0.04 has a shorter stroke that one with 0.08?
¿Does the stem move LESS with a TH set at 0.04 that with one set at 0.09? if so, WHY? is it because it hits the valve face?
I dont understand what limits the ammount of stem movement if not slaming against the valve face.
I could understand that a TH at 0.04 has less movement (stroke) that one at 0.09 because the one at 0.04 hits the valve front, while the one at 0.09 doesnt (or takes longer to do so), but if the TH does NOT touch the valve face, then why does one has a shorter stroke?
BTW, i ask this just out of curiosity, i dont really plan on messing arround with my TH forever. In fact, once i repair mine (grub screws damaged), i plan on leaving it arround 0.08 wich is (in my case) the best setting for kodiaks at about 930fps @ 2600psi fill, PW 2, or 970fps @ 2800psi fill PW 5. I get about 32 shots with an ES of less that 50fps with this setting.
i am using the tophat to change my velocity, and fine tuning with the power wheel, right now i am shooting cabelas h.p. at 900 fps, in the condor.
I have a oring behind the top hat to keep it from slamming into the valve body,tp at .080 with .071 oring behind it. i can close the tp down and get the vel to 450fps if i want. or open it up and shoot 1350.
most of the guys are shooting heavier pellets so their ideal top hat setting is for maximum velocity without waisting air. so mam’s suggestion is from his experience, is right on.for heavier pellets.
I had 3 guns set at .086 and they all had great bell curves…
the hammer/breech to open the valve further. It gives the valve a longer
stroke, and uses more air… Moving the tophat toward the valve moves it
away from the hammer/breech and reduces the amount the valve opens.
Shorter valve stroke, uses less air.. As WOK said…. Once you get the
tophat set, leave it alone….. 0.086″ gap is perfect…. The rest can be
done with PW, fill pressures, and hammer wieghts…..
Not trying to disagree with you but wanting to learn. What makes you say .086 is perfect?
Multiple opposing forces. TH height vs. valve/PSI resistance vs. hammer weight vs. PW spring preload.
A nice ballet dance, to be sure.
You are not opening and closing anything… Moving the tophat out allows
the hammer/breech to open the valve further. It gives the valve a longer
stroke, and uses more air… Moving the tophat toward the valve moves it
away from the hammer/breech and reduces the amount the valve opens.
Shorter valve stroke, uses less air.. As WOK said…. Once you get the
tophat set, leave it alone….. 0.086″ gap is perfect…. The rest can be
done with PW, fill pressures, and hammer wieghts…..
Viewing 11 replies - 1 through 11 (of 11 total)
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¿Exactly why does a TH of 0.040 produces less velocity that one wiht 0.080?
¿is it because the hammer has a longer run and so it impacts with more force?
or
¿is it because it lasts open longer? if so ¿why does it lasts longer open, if the TH doesnt hit the valve face?
I really like knowing how things work, so i Would really appreciate if someone could explain this to me, or point me in the right direction of what to read.
thanks!
Apparently the HAMMER TRAVEL of an extra 0.04 doesn’t significantly change it’s energy given the tanks internal spring tension. The Hammer strikes the Breech and Top Hat/Valve stem that is already resting against the delrin seal with about the same energy as it did with the TH set at 0.08. But it is moving the valve seal about 0.04 further open. The time it takes the valve seal to move back and forth the extra distance allows more air to escape down the barrel.
What is confusing at first is that we have 3 major components that are readily adjustable that can all interact together or in opposition in any combination.
With a given Pellet, Barrel, and Lubrication (or not), the 3 major components, PSI, Top Hat adjustment, and Power Wheel adjustment all have the potential of being TO MUCH, To LITTLE, or WORKABLE considering where the other settings are. Again, they interact on one another so that a high or low value may be offset by one or both of the others.
The delrin seal spring inside the air tank is a possible 4th variable but it’s much harder to get to and we can’t screw it up as easy. The combination of the internal PSI and internal spring holds the delrin seal closed and actually hold the TH, Breech, and Hammer slightly forward against the Hammer spring while at rest without being cocked. Like Buzzcat suggests, a dance and a balancing act.