Mechanical valve design

[sb327]

Yes, just another tuning option.

Dave

[mackeral5]

Yes, just another tuning option.

Dave

The only problem would be losing throat area, it is sized just over full bore with the 2mm stem, going to 3mm will put it just under.

More.to consider,.thanks for the recommendation

[sb327]

You can always just sleeve the portion that fits the stem guide, leave the stem diameter in the flow path small.

Dave

[mackeral5]

You can always just sleeve the portion that fits the stem guide, leave the stem diameter in the flow path small.

Dave

Adding a sleeve to that section of the stem, I had not considered before. 

I never intended to treat the veteran as a valve development platform and need to evaluate if I want to continue and if so what next steps are. 

I am curious to understand how increasing balance ratio effects the closing cycle.  This valve is currently a .150 chamber on a .290-ish sealing margin, peek poppet is barely large enough not to wedge in a .270 throat....

I have another valve with a .245-.250 throat, IIRC.  That would make a slight increase to balance ratio while not losing too much throat area, which with the 2mm stem would still be just under bore area.

[sb327]

I got one of the Jts aircuda max from Manny. It looks like it will be a good candidate for valve testing (at first glance). Seems reasonably modular.

Dave

[mackeral5]

I got one of the Jts aircuda max from Manny. It looks like it will be a good candidate for valve testing (at first glance). Seems reasonably modular.

Dave

That's awesome. 

Believe it or not, the Bulldog when removed from the stock is pretty good a development platform.  Plenty of room, simple valve access after degassing The only thing that is less than convenient is if you need to remove the valve retaining nut , which isn't required for most work.  I have some parts in process which will allow me to have 55-60cc plenum ahead of a 2024t3 tube, so my bulldog will more closely match my veteran long from a hp storage and plenum size perspective.  Hopefully this will reduce the trial and error the Veteran is exposed to...

[JPSAXNC]

I think the best attribute of a valve is a valve that will shoot a flat string without a regulator, that tells you that all of the mechanical functions are repeating consistently and that the valve is tuned.

[Motorhead]

I think the best attribute of a valve is a valve that will shoot a flat string without a regulator, that tells you that all of the mechanical functions are repeating consistently and that the valve is tuned.

Tho sadly achieving such a tune comes at the expense of Not having peak power one could have, or a way to reduce power if needed.
It's all fine within a very specific set up parameter, but altering any thing changes this Ideal balance of settings.

Generally how that plays out ... IMO 

[JPSAXNC]

Hi Scott, Then a regulator could be installed and the valve retuned, knowing that the mechanics were consistent. Just a thought.

[sb327]

I think unregged flat string tuned valves are some of the more elegant setups. If you’re going for a set/forget type gun that you want to do the same thing every time you use it, this type of setup seems like the more dependable/trustworthy.

I obviously like to adjust stuff all the time, lol, so adding the reg has become the norm for me.

I’m switching the Jts max to 22 so it’ll be a bit before I start experimenting with it. I’ll thread my own barrel (slug twist) and make a probe. The plastic mags are cheap enough.

Dave

[mackeral5]

These simplified balanced valves can act very much like a well tuned heavy hammer/small transfer unregulated gun.  Relatively flat ES across 1000psi pressure range at high energy levels.   

Except they can do it with light hammers, light hammer strike, and big ports.

Problem is, I haven't figured out the  exact recipe yet.  They want to run "where they want to run".  it is easy to find where the valve wants to run in a particular combination, but it may be above or below your desired energy level.  Consistently and predictably shifting the envelope, I do not have down to a science.  I can move it around through trial and error.  Vent size, chamber height/volume, those are the primary knobs to turn.  But for a given pressure/barrel lenght/desired FPE, I just have to guess at a starting point.

The valve will let you know when you are not hitting it hard enough, or over-powering it.....When you find the sweet spot, you can hear and feel it in the shot cycle.  And you will produce high energy for the application with low ES across a >1000psi pressure range.

[sb327]

I’ve definitely noticed that the lower the required input needed for a given output, the more magnified the discrepancies become. Which ends up in the form of extreme spread.

When designing a new valve, it’s usually just a WAG at what might work, lol.

Dave

[JPSAXNC]

Hi David, I just make simple knock open valves, And use peek toilet style poppets with a 3-5 degree angle on the poppet. And have the same problems with inconsistency if the hammer and valve return springs are to light. To over come the inconsistencies and get a flat string I use a valve return spring that takes 15 pounds of force to just crack it off the seat with no air in the gun, this flattens the bell curve peak.  I also use a metering lip on the poppet so that the area in sq. in. between the outside edge of the metering lip and the id. of the valve is .001-.003 of a sq. in. less than the  area of the valve throat in sq. in. minus the area of the valve stem in sq. in. My thinking was this would cause the poppet to close quicker conserving air. I also use a hammer de-bouncer. And then enough hammer spring to get the velocity want for the string by the first or second shot.

[sb327]

Interesting. So you are essentially creating more ‘sail’ effect?

Dave

[JPSAXNC]

Just enough sail effect in conjunction with the amount of poppet stiction and the valve return spring, to get the dwell time that will give me a flat string at a given pressure. And then the hammer spring determines the velocity and shot count of the string. At least that is how I think it all works. I have an 11" barrel and an 8" barrel I can swap barrels changing nothing else and shoot flat strings with both barrels. The 8" barrel well get about 25% fewer shots because the dwell time is to long for the shorter barrel and it wastes air. Putting in a softer hammer spring with the 8" barrel then gives me about 30% more shots at a lower velocity, and again the string is flat.

[JPSAXNC]

Here's two strings with the 8" barrel, This is wasting air. 693 696 697 693 696 697 695 699 697 695 699 693 694 697 This is with a softer hammer spring changing nothing else. 643 646 650 644 646 644 648 646 647 646 649 648 646 648 648 647 648 650 647 648 641 641 641 646 648 644 642 641 641.

[sb327]

Looks like it is in pretty good harmony to me. Thanks for sharing that.

I never considered sail effect as a tuning option. I have made provisions in one of my valves to shield the poppet from the effect.

Dave

[Motorhead]

Here valve retrofit into a RAW TM-1000X
This was built by RAW as a .177 at sub 20 fpe.  While they used the lighter Non X hammer the valve itself is the same one used in 22 25 30 caliber !!!  Huge throat and transfer path !!!
I've quite a few of these taking what is a large power plant that is just choked down at barrel to a more balanced configuration all the way to the barrel.

We make a new valve body from 7075 aluminum, drop poppet stem to .125", Throat at @ .240 and transfer at .150.  ( OEM was a .270 throat / .250 transfer )  Poppet head is PEEK and has the cobraa chamber as one piece.  Seals on a 15* concave seat surface.
End cap modified removing the poppet spring holder stem, pocket made for a Delrin stem that carries the o-ring to seal the chamber.  Side of poppet at floor of chamber gets a .052" vent hole.
Restriction donut added between valve and barrel within receiver.  This has the TOTALITY of transfer path at .150", saves a buch of air with pretty substantial gains in overall efficiency.

Super easy to open, snaps closed quite fast. SSG device added and a peek strike tip installed on hammer nose.  Super clean way to do this type valve & mod

[sb327]

Nice work. I’ve noticed with a lot of ‘factory’ type setups, the one size fits all approach means it works fine for one size but not so much for the rest. And there are definitely a lot of sizes from .177 sub20 up to a 30cal!

Dave

[JPSAXNC]

Scott, Do you think that a 7075 aluminum simple knock open valve in a pcp could use a peek toilet plunger style poppet, without damaging the valve seat?