Tuning Impact PP valve puppet

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bigHUN

bigHUN

Member
Jan 16, 2020
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L4G7X4 Canada
Finally got all my parts on pile and ready to start with porting mod.

The stock valve seat hole is 6.5mm, and the valve puppet OD 7.5mm, valve house ID 10.63mm.

If I re-drill the seat to let say 7.2 can I keep the same distance to the edge of the puppet or to make it larger for couple tenths, to let say max 8.0mm?

I know where is a read about this discussion couple months ago but my memory faded waiting too long for spare parts. Where you folks ended up with trials?


 
A sealing margin of only 0.4mm (0.015") is getting a little aggressive. Depends primarily on the operating pressure and poppet material. Neither of them is specified but I'll present a hypothetical. At a 140bar (~2000psi) regulator setpoint, the rim of an 8mm poppet over a 7.2mm throat is carrying a load of about 9000psi. That's probably fine with PEEK but may be overstress Delrin. Reduce the pressure and the loading goes down proportionally.
 
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Sorry yes you are right, my error with the number...

Right now under all stock conditions the perimeter seal is 0.5mm wide. Following that logic the puppet OD shall be 9.065mm.

That is feasible.

I am planning to get a new puppet in peek, also will order a brass "pin" rod to lap/polish that same front angle/cone to the valve seat.

At this moment the optimum speed is 920 fps with .25 cal JSB MK2 Heavies and 700mm barrel, last time I checked the reg was about 118 bar, today is a lot colder.

I don't plan to reach 140 bars I have no need for that, not for now, only to make the extra power/numbers available for - optional calibre jump.
 
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I have drilled my VS to 6.1, on my MK1 running the stock poppet, and my .25 700mm will shoot the 36.2 NSA slugs at over 1000fps at about 130 on the reg. I have one of Michals plenums installed as well. That is over 85FPE with a middle of the road weight slug. So, a 6.5mm VS will do much more than that so long as your barrel port will allow it.

How much do you need?
 
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Bear in mind the larger you make the throat, the harder it is to knock open the valve (more hammer spring tension needed). There is no benefit to having a larger effective throat (throat area minus valve stem area) than either the valve’s exhaust port, the transfer port, or the barrel port. Perhaps a tiny bit bigger, but not much.
 
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I wanted only the Valve Housing + Valve Pin/puppet + Rear Block as to prepare the porting changes/machining on the spare parts, and just replace the remaining originals within a minimum time. but it was just way more convenient getting the entire PP kit (I could not collect all these from a single source otherwise).

Lot of parts I already replaced in the Impact MK2 PP and having spare parts is always good.


 
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