FX hammer spring adjustment question

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There a plenty of people here that can give you a better explanation. But here is a simple way to think of it. It isn't so much what is happening "in there" as it is, how you effecting what else is happening in the gun. Imagine the power increase like a bell curve. As you go in on the spring and create more tension, you are throwing the hammer at the valve pin harder and it opens more. So you are going up one side of the bell curve. As you continue, you reach the top of the bell, the fastest the reg pressure and spring tension can make the pellet go. But when you continue past that, now you are what is known as "past the knee of the bell" and you start on the down side again.

What is happening then is, you are already opening the valve as far as can be "used" to push the pellet. Now, more hammer spring makes the hammer hit the valve pin so hard, it knocks the valve open TOO far and you start getting "dwell" or the valve traveling too far in and back, spending unnecessary time open. That condition just wastes the air and doesn't help with the speed at all. 

To get on top of the knee, you go in until you start to lose velocity, then back out about 1/2 turn. (this is just general and not a hard rule). At that point, you will be at the max the gun can do with that reg setting. There are many other things like port size and the like to consider, but I'm trying to give you a simple explanation of what is happening.



Hope that helps

Crusher
 
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Great explanation crusher, and you may be right. I think of it differently. 

I always thought that when the hammer was stronger than needed to open the valve with a slingshot hammer like fx has, it hits it very hard. Hard enough that it super quickly opened the valve, and because the hammer is slingshot it doesnt keep it open like a tensioned hammer would. Instead the valve opens super fast and then rebounds and closes at its regular speed.

So in essence the valve is open for a shorter amount of time, and lets less air through the gun because of its rapid violent opening vs. the controlled push open a well tuned gun has. 



What are your thoughts on this?

best

keith
 
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I know some do max out the hammerspring adjustement mechanically on guns like impact, or crown, and start with wheel on max, before tuning for high power. I personally would not do it, as it might could cause damage to the gun, if the valve overtravels. It is better to do it safe, increase step by step, so there is always a balance between hammerforce and regpressure.
 
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Thanks Crusher / Keith. This isn't the case with other makes and just makes me wonder what's going on. I even wondered if it was just dumping all the available air in the plenum, and the air rushing in from the reg was closing the valve quicker? Or like Keith said, maybe just bottoming out the valve spring and its bouncing back quicker. Interesting to me anyway. Because normally, more hammer strike = more dwell.
 
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Many other manufacturers have this same outcome once you over tension the hammer spring past the speed plateau. In fact, I would say most regulated guns behave this way. Some are more apt to show this sooner and more definite than others. I believe the smaller your plenum (regulated air space) is, the more compelling this velocity drop will be (a lot of FX models have small plenums).

My analysis tells me that what is happening in this situation is; as you dial in more HST (hammer spring tension) the valve dwells more. You reach a point where you are creating enough dwell to expel all of the plenum supply (a good thing). All this pressure empties and then the regulator allows the plenum to fill again which is a slow process (few seconds) compared to the shot cycle (milliseconds). 

Now, dialing more HST at this point, creates an over-dwelling valve. You’ve emptied the pressure supply from the plenum which is now unfolding compressed air down-stream. Instead of closing the valve immediate, giving this charge of energy no other avenue of release rather than behind the projectile and down the bore, the valve hovers open too long. The plenum is empty and has relatively no pressure in it, the charge of air is expanding as it decompresses, looking for an escape. With the valve still in dwell, a portion of this charge re-enters the plenum up-stream thus lowering velocity down the bore. 


 
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Many other manufacturers have this same outcome once you over tension the hammer spring past the speed plateau. In fact, I would say most regulated guns behave this way. Some are more apt to show this sooner and more definite than others. I believe the smaller your plenum (regulated air space) is the more compelling this velocity drop will be (a lot of FX models have small plenums).

My analysis tells me that what is happening in this situation is; as you dial in more HST (hammer spring tension) the valve dwells more. You reach a point where you are creating enough dwell to expel all of the plenum supply (a good thing). All this pressure empties and then the regulator allows the plenum to fill again which is a slow process (few seconds) compared to the shot cycle (milliseconds). 

Now, dialing more HST at this point creates over-dwell on the valve. You’ve emptied the pressure which is unfolding compressed air down-stream. Instead of closing the valve immediate, giving this charge of energy no other avenue of release rather than behind the projectile and down the bore, it hovers open too long. The plenum is empty and has relatively no pressure in it, the charge of air is expanding as it decompressed looking for escape. With the valve still dwelling a portion of this charge re-enters the plenum up-stream thus lowering velocity down the bore. 

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Agreed. And in some cases (large plenum), as the dwell increases, the pellet is gone, down the barrel and out. The air is just rushing out not pushing anything. At that point we can start talking about the way the tune sounds. I can tell when a gun reaches the above condition by the sound it makes. I suspect many of you can tell when the gun "sounds right".

I have found that when I have the condition of "too much air", it usually affects the accuracy. The blast of disturbed air behind the pellet can disturb the flight of the pellet. But then, we aren't talking about the O P. :)



Crusher




 
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Let me chime in here. I've read the explanations above and the one I agree with the most is @tor47 . I've read and understand the other explanations, but having the valve stay open too long and dump excessive air into the transfer ports and barrel wouldn't slow the pellet down IMHO. How would that work? The pellet has already left with a specific amount of air, and then as dwell increases its putting more air behind it. That could affect accuracy by having turbulent air behind the pellet as it exits the barrel, but I'm not seeing how that would slow down the pellet or cause it to be traveling at a slower velocity.

It does make sense to me that as HST increases to a certain point, we get to the "plateau" of the HST/velocity curve, since past the knee and onto the plateau, further spring pressure doesn't open the valve any further or any longer. But to keep going until the spring tension causes the hammer to fully compress the valve spring to the point that it causes the valve to "bounce" at the end of its travel and start closing faster than it normally does would cause the valve to shut sooner than with less spring tension and result in less dwell and a lowering of velocity. My two cents... ;)
 
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Let me chime in here. I've read the explanations above and the one I agree with the most is @tor47 . I've read and understand the other explanations, but having the valve stay open too long and dump excessive air into the transfer ports and barrel wouldn't slow the pellet down IMHO. How would that work? The pellet has already left with a specific amount of air, and then as dwell increases its putting more air behind it. That could affect accuracy by having turbulent air behind the pellet as it exits the barrel, but I'm not seeing how that would slow down the pellet or cause it to be traveling at a slower velocity.

It does make sense to me that as HST increases to a certain point, we get to the "plateau" of the HST/velocity curve, since past the knee and onto the plateau, further spring pressure doesn't open the valve any further or any longer. But to keep going until the spring tension causes the hammer to fully compress the valve spring to the point that it causes the valve to "bounce" at the end of its travel and start closing faster than it normally does would cause the valve to shut sooner than with less spring tension and result in less dwell and a lowering of velocity. My two cents... ;)
Click to expand...







Agreed. The velocity drop is what had me puzzled. Normally report gets louder and your just wasting air after elvis has already left the building.

Thanks to all.
 
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Let me chime in here. I've read the explanations above and the one I agree with the most is @tor47 . I've read and understand the other explanations, but having the valve stay open too long and dump excessive air into the transfer ports and barrel wouldn't slow the pellet down IMHO. How would that work? The pellet has already left with a specific amount of air, and then as dwell increases its putting more air behind it. That could affect accuracy by having turbulent air behind the pellet as it exits the barrel, but I'm not seeing how that would slow down the pellet or cause it to be traveling at a slower velocity.

It does make sense to me that as HST increases to a certain point, we get to the "plateau" of the HST/velocity curve, since past the knee and onto the plateau, further spring pressure doesn't open the valve any further or any longer. But to keep going until the spring tension causes the hammer to fully compress the valve spring to the point that it causes the valve to "bounce" at the end of its travel and start closing faster than it normally does would cause the valve to shut sooner than with less spring tension and result in less dwell and a lowering of velocity. My two cents... ;)
Click to expand...

So knocking the valve open further with a harder hammer strike is closing the valve faster, in your opinion 😁 Not buying that one.


 
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Not exactly. Knocking against the hard stop of the fully compressed spring or full valve travel is bouncing it back towards the seat is what I intended to say. I’m sure you’ve experienced hammer bounce just postulating that it’s possible to experience valve bounce? ;) This is theory anyway, and we’re all just guessing. I’ve never seen it go down when I increased HST, only level out. Since once it starts leveling out, I stop and return to the knee of the curve. 
 
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