FX IMPACT: VALVE VS HST

[Drumsnguns]

Sorry if this has been discussed before., so I'll make it quick.
I see videos where tuners say, for slugs, leave the valve all the way open with a slight turn in, (but basically it's wide open).
If you're wanting to zero in on a particular velocity and are maybe 5-10 fps high, would you dial in the Valve knob until you hit the desired speed or would you leave it alone and back off the HST a bit?
Easy enough to try myself really, but wanted an opinion
Thanks.....

 

[Airgunmann]

Sorry if this has been discussed before., so I'll make it quick.
I see videos where tuners say, for slugs, leave the valve all the way open with a slight turn in, (but basically it's wide open).
If you're wanting to zero in on a particular velocity and are maybe 5-10 fps high, would you dial in the Valve knob until you hit the desired speed or would you leave it alone and back off the HST a bit?
Easy enough to try myself really, but wanted an opinion
Thanks.....

I would turn in the valve knob to take off the top few fps it seems to work better tuning that way on the impact I'm sure others will have there opinion to

 

[Chuck-in-Ohio]

I did exactly that, but with pellets.

Use the valve adjuster to drop back your max fps to stay in the sweet spot of the curve for your reg setting.
Making an adjustment of over 15 fps or so, I use the hammer spring adjuster to find max for the reg setting, then fine tune for the sweet spot with the valve adjuster.

Stuff that I learned here, back in the days of Impact madness.

 

[Vetmx]

This has not specifically been discussed before to my knowledge. At least not in detail. As you know, there are several ways to arrive at a certain speed. But even if you believe you know the perfect speed, how you arrive there can have drastically different results. Without going into detail about trying to find the right speed and how, once you have a speed range narrowed down, you can test it two ways. I have Impacts in the other room that are not all tuned using one way. One likes more hammer strike with more dwell shut off with the valve. Another likes about the same hammer strike, on the plateau vs the knee curve also. But very little leaning on the valve. But still some. The other Impact likes the classic tune. Hammer strike is probably right around the knee and moderate valve tension.

Now we get to the side effects. Gun “A” has non factory plenum parts and suffers no first shot blues. But I have to keep an eye on the rubber balls in the valve knob. They are getting smacked. When you start getting to those balls with how the gun is tuned, you have to watch out for an increase in velocity during long shooting sessions. When you see that and don’t want to give up a spectacular tune, you can do another little mod to negate it. Gun “B” also has first shot plenum mods and has no first shot blues. And because it shoots its slug great without a lot of valve knob, it’s a steady Eddie no matter how long you shoot it. Gun ”C” has first shot plenum parts but it still suffers the first 3 shots blues because of where the hammer is set. But it is so accurate with the hammer closer to the knee that I’m forced to live with it. I’ve tried reduced reg and more hammer at the same speed and the gun is just not as accurate or consistent. So now I just turn my wheel up two clicks for a first shot if he gun has sat an extended time. And this is why we don’t tune our guns and finalize the tune with the wheel on Max.

So in a nutshell, figure out what gives you the results you can live with. The Impact is a gun that will always have a side effect. No matter what you do with slugs, you always wind up paying the piper in some way. You just have to figure out how to pay him the least amount possible. Gun “B” is probably what guys who read this are thinking yep, that’s how I’m going to tune mine. If it was that simple, all three of mine would be tuned that way. But every gun slug combo is different.

 

[Chuck-in-Ohio]

@Vetmx

At what point do you start to notice the rubber buffer starting to get knackered, or, how hard are you leaning on the valve adjuster before you get that effect?
I have never choked one off more than 10 to 15 fps with the valve adjuster,,just a bit under wide open really.

Thanks for the run down, it has been a while since I hand jived either of my Impacts.

 

[Vetmx]

@Vetmx

At what point do you start to notice the rubber buffer starting to get knackered, or, how hard are you leaning on the valve adjuster before you get that effect?
I have never choked one off more than 10 to 15 fps with the valve adjuster,,just a bit under wide open really.

Thanks for the run down, it has been a while since I hand jived either of my Impacts.

Depends on the reg setting, aftermarket hammer spring, hammer weight, probably barrel length, projectile weight or caliber. The easiest way is to take a peek at them. My guess is nobody does. They are a nifty idea but if you aren’t lucky enough to arrive at a great tune/accuracy perfectly, they are another one of the Impacts Achilles heels.

 

[Chuck-in-Ohio]

Depends on the reg setting, aftermarket hammer spring, hammer weight, probably barrel length, projectile weight or caliber. The easiest way is to take a peek at them. My guess is nobody does. They are a nifty idea but if you aren’t lucky enough to arrive at a great tune/accuracy perfectly, they are another one of the Impacts Achilles heels.

Thanks for sharing the info.

I never really gave much thought to the buffer, but will take a peek to see if anything is amiss after your input. I have not gone past the bottom of the last line, but in my .25 compact, the hammer smacks the valve with some authority. It is launching the MKlls at 890.

Thanks again for the insight.

 

[MongooseV8]

I think the key is to keep the valve stop adjusted to the point where the spring just kisses the valve rod to slow it down without bottoming-out on the rubber ball. There is no way to know when you get there, but it sounds good on paper. I keep mine mostly full open, especially on my slugger that is setup with a stout hammer strike. But if you want to reign in a handful of fps from full open, I think thats really how it should be used in most all cases. I dont really see it as a Valve Stop, more of a Valve Rod Slower-Downer. If you have a low fpe setup with dainty hammer strikes you can close it down further. But there is no way to avoid the cold reality of part service life; and the more you abuse them the quicker they need replacing.

 

[Drumsnguns]

I wanted to get back on this issue. I turned the knob in and the velocity started to go up which I have heard about in some tuning videos. I noticed that it took a lot of turns to start to bring the speed down, (now just north of line 2), but I had to back off the power wheel one click down to 13 to get into the desired range. But the groups weren't as tight with ZAN 41's (.25) so I went back up to 14 and groups tightened back up a bit. Thinking I might just set the valve back to 8.30 mm as it was shooting pretty darned good there at around 960 fps. I had been hoping that the valve might have magically gotten me one hole groups at 60 y but that just doesn't seem to be reality, haha. Maybe I'll go the other way and back it out a bit more. Who knows???

 

[Drumsnguns]

I did exactly that, but with pellets.

Use the valve adjuster to drop back your max fps to stay in the sweet spot of the curve for your reg setting.
Making an adjustment of over 15 fps or so, I use the hammer spring adjuster to find max for the reg setting, then fine tune for the sweet spot with the valve adjuster.

Stuff that I learned here, back in the days of Impact madness.

Impact madness...that is an accurate statement.

 

[airgunstop.com]

...back in the days of Impact madness.

Very true, we could not keep them on the shelf with delivery lead times over 10 months during the COVID period.

 

[Chuck-in-Ohio]

I was referring to the period when the first gen. Impacts and Impact X were the top of the line, and the first power plenums were coming onto the scene. The MKll Impact was king of the hill and everyone was pushing the envelope with tunes and upgrades.
Impact madness revolved around whatever Ernest Rowe had stirring in his workshop, and several threads on here where guys were deep diving into internal mods for more juice at the muzzle.
I also remember the lockdown madness where ALL anyone had to do was tinker till their heads fell off......