Valve Knob on Impact_Confused

[Drumsnguns]

Gosh, I don't really know when to use the valve knob on the .25 Impact. My gun is set up at 145 bar on the reg and the HST is matched to that reg setting which I think is 15.26mm and the valve knob set on or just a smidgen under 4 bars. With the X-barrel, I can't go any further out because the valve knob bumps into the back of the shroud. It did not do this with the original ST barrel . Same shroud but it fits the X liner a bit differently. This gives me 895 fps average with an ES of 7 and an SD of 1 with JSB MKII.

When I start to turn in the valve to the point speed starts to drop, which should be an efficient setting....my ES jumps up to like 18.

So back it goes to right at 4 lines, the ES is back down.....so I think I'll forget about the Valve Knob. I've never really messed with it since I got the gun. To me the valve knob seems like a screen door on a submarine? But of course it must play a significant role. I've never seen much talk on the forums about it. Matt Dubber says when tuning just leave it alone....haha.

Can anyone shed some light? Apologies for the my ignorance.



KP

 

[jtnm]

I have mine set at about 3.5-3.25 line. If I was you keep taking it in to see if you find the sweet spot. Don’t remember exact fps, On mine at 4th line or tad greater say it was 880fps with HS at max with reg setting etc, I started to turn in Valve knob seen it drop velocity like it should, I just keep going in 1/8th of turn or so, then around 3.5 Mark I seen velocity come up to 895-900fps. Keep taking it in until I dropped below that probably to 2nd line, then found that max again and called it good at 3.25-3.5. Actually both my impacts are similar with valve knob settings, pre-impact X and impact x. 

 

[Drumsnguns]

I’ll give that a try. Thanks for the tip. 

 

[tor47]

Think it is helpful if tune your gun with high repressure and light hammer strike. You adjust the hammer spring first, and turn in the valve adjuster lowering the average velocity maybe 10 fps, to make valve open and close more presisly. That might make the gun shoot with less velocity variation.