The SAM Valve

[mann]

I've went down to .080 on my  Marauder 25 and had no problem with it at one time I remember reading some one running a stem down to .040 on a marauder and was having good luck with it

[TroyHammer]

If throats already .263" then its pretty settled to handle that thick stem in the valve throat.

That said, with a .125" stem, the .263" throat could handle porting up to .225" which is where I have my valve, but I use .234" throat and a .055" stem lol with peek on the poppet. Super easy to crack for the power it pushes out on traditional valve. Of course that kind of porting takes oblong work and about 10 degree offset angled to the back of the valve, and a bit of breech widening for a custom tp, but theres enough room to have healthy walls on a tp that fit snug in the valve/barrel inserts which Iirc are around .28", leaving .02"-.025"~ for your tp walls.

Its a limit pusher but mines held up great for the last 2 years.

Sent you a PM

[PikeP]

I've went down to .080 on my  Marauder 25 and had no problem with it at one time I remember reading some one running a stem down to .040 on a marauder and was having good luck with it

Ya thats me, I try to keep the minimum od to .05" now, the .04" I had in my Marauder was fine but I changed to .05" when changing to a .225 ported valve over a .212 valve. Old poppet was .25" OD and didn't work out on a .234" throat/seat, so redid poppet at .275" with a .05" stem. I like to push limits though, and that is extreme. Although now that I've had it running for a few years without fault, I would recommend anyone take all stems down to in the throat for airflow and to allow larger porting on smaller throat od's, but one must consider your intended hammer energy levels / force holding the valve shut ect, but nominally I can see .045"-.075" working fine for most applications till you approach really high power levels, at which point you should balance the valve, which would bring you back within aforementioned usable stem od margins.

Anyone that has gone down that road tends to not go back as its value has plenty merit in our application. I consider it a part of the process in making a poppet just as much as any other step.

 A large valve stem in the throat has unnecessary volume which not only requires larger seat diameters that increase hammer energy requirement, it also deflects more of the air path than the smaller counterpart, think of the stem as having a thin layer of skin that no air can travel over, the thicker the stem the more surface area the skin has. As marginal as the difference is, most of us will take an fps or two when we can even by finely tuning our air paths to the best of our ability where we can. It creates a slightly more efficient air pathway.

[FuzzyGrub]

I did find a couple of pieces of steel rod that someone gave to me for poppets.  It is only 0.076" dia, and don't have brass tubing that small. 

The test valve is set, but the mods to the SAM valve are not final.


Matt,  I'm curious to the power level that your 25 valve achieves. 

[mann]

My raw valve is .260 ish throat and .325 peek poppet about 55 cc with power plenum running a .123 ish stem in the throat cobra chamber mod also at 150 bar it was over 950 fps with Huma reg at 125 bar I'm running 905 fps with barrel being choked point at .200 port so 60 ftlbs at 62 shots with 34 gr jsb mk2 pellets it isn't the greatest efficiency but it does ok I also lightened the hammer to 60 grams from the original hammer if I pushed it I bet I could get to just over 1000 fps about at 150 bar but I don't need it so I don't

[mann]

Pike what kind of power and efficiency out of yours being more well versed in this are you getting I'd be interested too seems like you know your numbers really well which has me intrigued

[PikeP]

I did find a couple of pieces of steel rod that someone gave to me for poppets.  It is only 0.076" dia, and don't have brass tubing that small. 

The test valve is set, but the mods to the SAM valve are not final.


Matt,  I'm curious to the power level that your 25 valve achieves. 

For the stem bore I wouldn't go under 7/64 myself, going down from .195" to .125" will take a huge load off (half the force acting upon the stem during valve open), but on an unregulated gun will reduce the bell curve / psi range.... and only reduce the stem to .076" inside the throat where its exposed to port pathing. Really depends what you want out of the gun. If going regulated you can go further.

Pike what kind of power and efficiency out of yours being more well versed in this are you getting I'd be interested too seems like you know your numbers really well which has me intrigued

This was the last string I ran, all my guns data is on here. I am running 140 bar now though with a bit more power (66 fpe peak) where as this one was 135 bar~ or so with 63~ fpe peak.

[FuzzyGrub]

THX Matt,  That is quite the spreadsheet.  Nice!    

I'm targeting low 50's

[PikeP]

THX Matt,  That is quite the spreadsheet.  Nice!    

I'm targeting low 50's

Thanks.

I'm doing that 60 fpe on a 7.7 lb spring with .6~ preload and a 49 gr hammer. 4.6 lbs cocking force to start, 11.165 lb finish. Very reasonable  for a traditional valve making that kind of power.

If I were to target low 50's I'd run the same exact setup as I have now at 125 bar, valve would open a bit easier and probably get nearly 32 shots on a fill from 3250~ (about where I fill my mrod). Its attainable.

One of the key features I like about large ports, is you can really extend your usable psi range with those valves by running lower regulated pressures than a smaller ported counterpart, which frees up usable psi. Without a retracting probe, the largest I could go was .225" on an mrod with gen 1 style bolt modified.

Our air path flow rate variables are effected  primarily in the following order

1) Port pathings (diameter)
2) Pressure
3) Bends (not relevant to as we don't add or remove bends but their presence greatly effects flow rates)
4) Obstruction efficiency in airway (valve stem and bolt probe)

Any drop in diameter from bore causes flow loss, the further from bore diameter you get, the more you have to raise pressure to start making back the power you had before, and vice versa, if one were to reduce pressure in a valve, you'd want to increase the port size to regain the flow rate, or vice versa (a pressure increase requires reduced pathway to retain same power).

So at least in regulated applications, it really is only beneficial IMO to have your ports as large as reasonably possible, regardless of desired power.

[FuzzyGrub]

Yes, I am currently gated at the bore with the standard G2 25 cal bolt which has a 0.160" probe.  I was going to sleave a 22 cal bolt which has a 0.125" probe.   I do have a G1 25 cal flow through bolt, but it would seem to need some considerable grinding to get to the equivalent cross-section area.  This will be just a pellet shooter, JSB 34g.

Any retracting bolt would need some machine work to the breech, which would be a "big" challenge given my tools.

[FuzzyGrub]

While the "plugged" test valve hasn't failed yet, decided to take advice and not do that to the SAM valve.

I sleaved the poppet stem hole with some brass tubing.  Reduced the oem poppet stem to 0.100" below the poppet seat, for the 0.225" pocket.  Oblonged the exhaust from the pocket to a 0.200" TP.   Kinda like a three sided funnel to stay away from the oem seat.    Valve countersunk to 0.26", like the test valve. 

I did order some 1/8" steel rod to try a peek poppet in the future. 

PS:  I put the info in the spreadsheet and will take the poppet stem to 0.080", as Mark did, to get 10% greater than the TP cross-section.