The SAM Valve

[Rob M]

interesting , thats one classy looking valve in the sam

[PikeP]

If the stem is a tighter fit I'd ditch the oring it can mess with extreme spread  just my opinion

+1

[FuzzyGrub]

If the stem is a tighter fit I'd ditch the oring it can mess with extreme spread  just my opinion

+1

If high Es is my only issue today, it will be a good day.

The “donut” was under vice pressure while the epoxy set and cured, but whole different thing when it is 2-3k psi and the dynamics from shot  to shot.   I did use the "steel reinforced" epoxy which has the higher rating of 5000psi. 

I will say, the stock poppet when in Akela, produces some of the lowest non-regulated Es I’ve seen.   Very different dynamics though.

[PikeP]

If the stem is a tighter fit I'd ditch the oring it can mess with extreme spread  just my opinion

+1

If high Es is my only issue today, it will be a good day.

The “donut” was under vice pressure while the epoxy set and cured, but whole different thing when it is 2-3k psi and the dynamics from shot  to shot.   I did use the "steel reinforced" epoxy which has the higher rating of 5000psi. 

I will say, the stock poppet when in Akela, produces some of the lowest non-regulated Es I’ve seen.   Very different dynamics though.

The reason your Akela or any gun with a thicker than 1/8 valve stem can achieve a very low ES relative to a 1/8" stem is because the added closing force that occurs over the duration of the valves dwell...it absorbs minor fluctuation of hammer energy better than a stem with less force acting on it over that time period (think of a pellet in the wind and time as a factor just as much as your stem and pressure acting upon it with dwell).

Makes me wonder how a balanced valve with a 9/64" valve stem would perform, and if that would potentially reduce the variation caused be 'break-out friction'. Then again, thats off subject, but just food for thought for any who reads.

Thicker valve stems (ideally not in the throat, only in their bore) also respond to hammer strike changes much less than thinner valve stems, meaning it takes more preload to go up or down 100 fps on a thicker valve stem then a thinner one. These two MAJOR 'effects' are due to the 'cause' of the valve stem.

Assuming the stem + oring are the od of the bore as mentioned earlier, .132" has around 10% more force acting upon it than a .125" stem.

[FuzzyGrub]

I shot three mags and no big surprises, with the test valve.      I'll keep shooting it, to get a few hundred cycles on it, before starting work on the SAM valve.  There are a couple of things I will do differently, process wise, and it will also be a little easier given the shorter depth.

Yes, it will need more hammer energy, but thought most of that would be because of the larger diameter sealing surface.  I wasn't aware that stem diameter also plays a role.  The Akela poppet stem is 0.195" at the large diameter, and a smaller diameter of 0.155" at the flow path.  I opened the poppet hole for the larger diameter stem.   From my test shots, I'll be going up on hammer weight. 

[TroyHammer]

I shot three mags and no big surprises, with the test valve.      I'll keep shooting it, to get a few hundred cycles on it, before starting work on the SAM valve.  There are a couple of things I will do differently, process wise, and it will also be a little easier given the shorter depth.

Yes, it will need more hammer energy, but thought most of that would be because of the larger diameter sealing surface.  I wasn't aware that stem diameter also plays a role.  The Akela poppet stem is 0.195" at the large diameter, and a smaller diameter of 0.155" at the flow path.  I opened the poppet hole for the larger diameter stem.   From my test shots, I'll be going up on hammer weight.

From my experience with the akela the hammer is already too heavy. The Kral hammer is 45gr and will do 60 shots in 22 at 30+fpe the akela hammer from my gun iirc was like 60gr. Both using the same valve, poppet and stem.

Edit: I thought you were comparing missed the part where you installed the akela stem in an m-rod valve.

[FuzzyGrub]

Edit: I thought you were comparing missed the part where you installed the akela stem in an m-rod valve.

No problem. 

I would like your opinion on why you think they went with such a large poppet on these guns given the small caliber.   Faster closing time?  or just over-built to prevent breakage?   

[PikeP]

.195 stem in the bore is massive, holy. that explains a really nice ES

A bit excessive but really drives my point home on how much stem diameter plays in taming ES (talking to you balanced valve guys)

[nervoustrigger]

I hadn’t been following this thread but will now.  The stem diameter’s influence on closing force and ES has come up from time to time but so
infrequently that it seems to be largely overlooked as a tool when modding and tuning.  Especially when the goal is to squeeze out those last few FPE, it’s tempting to go ever smaller with the stem. 

[TroyHammer]

The kral valve is an Evanix Rainstorm clone so I doubt much thought was given other than the material. They did reduce the throat from .300 to about .275 on the newer guns as well but haven't done a direct comparison on what that means. It definitely cracks easier but I don't see a huge difference in ES between the two styles.

[mann]

.195 is bigger than alot of transfer ports are I'd sleeve it to .125 and not look back

[FuzzyGrub]

For now, I'm stuck with this poppet.  I would have to make a custom poppet to replace it.  So, for supporting a 0.200" dia exhaust port, what should the pocket dia should be?   Ie should the cross-sectional area be 10-20% more than the exhaust? 

[PikeP]

For now, I'm stuck with this poppet.  I would have to make a custom poppet to replace it.  So, for supporting a 0.200" dia exhaust port, what should the pocket dia should be?   Ie should the cross-sectional area be 10-20% more than the exhaust?

Sleeve it and make a custom poppet, imo they are quite easy to make, and white delrin is stronger than black by about 20% fwiw, its what I use if going delrin, and can be had cheaply at grainger for 1-2$ per foot.

Black delrin yield: 9k psi
White delrin yield: 11k
Peek yield: 16k

For a .2" port, the throat should be .26" if your stem OD in the throat is .155" as you stated earlier.

Pretty nuts.

I would sleeve the poppet bore to .125", make a custom poppet, have it be around .11" at most in the throat...then your throat would only need to be .234", which will be a lot easier to crack than the above version. I got an extra long 1/8" drill bit from Harbor freight for around 5$ that can make about 8-10 poppets (12 inch drill bit lol)

So the above can be done really inexpensively, just a bit of time.

[mann]

I've used a chunk of cold rolled 1/8 in steel round bar from hardware store for poppet stems working good

[FuzzyGrub]

For a .2" port, the throat should be .26" if your stem OD in the throat is .155" as you stated earlier.

I'm at 0.263", which is about 12% larger cross-section.  When I saw Troy's comment about the valves having 0.300" and 0.275", got me wondering. 

I have some peek and black delrin, but would need to get poppet stems.  This poppet has a taper on the sealing surface for an edge seal.  Not sure I could do a good job of the taper with caveman tools. 

[mann]

No need to get fancy mine are just press fit into peek a couple thousandths and clean them up with some sand paper and drill then polish .002 .003 under 1/8 inch isn't going to cause a big enough leak to worry about for short time it is open 

[mann]

Derlin is pretty forgiving when it comes to sealing up but I understand your worry

[mann]

The other things I've done is turned down the old poppet stem using a drill press and a file takes a bit to get it right though

[mann]

That was before I got a lathe though

[PikeP]

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.