Simplified Balanced Valve

[rkr]

Hmm, i do have pretty good fps spread right now ... perhaps I'll start with bench rest stock and see if that's enough to get rid of those flyers caused by me and trigger not being in sync.

[skorec]

If  balance valve  increase the power at about  30% the ES have increase at about 30% too .

[PCPhack]

No it doesn't.

[Motorhead]

No it doesn't.

Would agree ... percentiles of cause and effect are not proportional to power produced.
Tho said, if the tune is really out of balance the ES very easily could be much worse than an out of balance conventional valve.

Every thing is amplified if out of wack ... Tho with correct tuning and balance of parts they can be just a stable and low ES as a conventional valve.

[skorec]

YES practical experiences are most importance.

Another theoretical ideas for poorer ES for balanced valve  :
1.   Longer valve dwell mean also higher difference between individual  dwells .
2.   Small venting hole and balanced chamber may  be not stable via different temperature or dirty
3.   Sealing O-ring may add different dragging

I see only  one idea for better ES may. Lower spring tension that may be  means also lower/less difference at hammer string energy.

[Motorhead]

YES practical experiences are most importance.

Another theoretical ideas for poorer ES for balanced valve  :
1.   Longer valve dwell mean also higher difference between individual  dwells .
2.   Small venting hole and balanced chamber may  be not stable via different temperature or dirty
3.   Sealing O-ring may add different dragging

I see only  one idea for better ES may. Lower spring tension that may be  means also lower/less difference at hammer string energy.

Your beating this horse unnecessarily ....... Read up on the valve and most of what you think is going on will become clear as to what actually is going on   
Start by reading this thread from the beginning.

[rsterne]

If  balance valve  increase the power at about  30%

Simply stated, it doesn't increase the power, all it does is reduce the hammer strike.... You need to read this thread to understand what is going on....

Bob

[skorec]

I know and sorry because  I again  forgot to mentioned/accent “if”. If the hammer strike energy is the same we can use higher shooting air pressure  which produce  the higher bullets energy. 

For me using higher shooting air pressure for slugs is tautology and main reason why to use balanced valve.
Sorry again.

[Scotchmo]

.... It is becoming increasing more obvious that you can't make the chamber too small, ...

I'm going to take exception to that statement. Yesterday I made some changes to the porting outside the valve. The only change I made to the valve on that  tear down was to reduce the balance chamber volume. After doing so, the gun would no longer produce ANY significant energy. Occasionally, it would fire, though very low fpe. If I really leaned on the hammer, it would fire more often but still very low energy. I think I was at the point of the balance chamber volume being TOO small for any significant assist.

This is what I had when it was working more consistently:
Balance chamber volume
valve closed: 0.1016cc
valve fully open: 0.0295cc

This is what I had when it would no longer work as a balanced valve:
Balance chamber volume
valve closed: 0.0836cc
valve fully open: 0.0115cc

That is a very small change. I'll speculate that the poppit had insufficient time to escape the Bernoulli effect before the small balance chamber pressurized.

I switched back to the larger balance chamber volume, and that fixed it.

I'm going to try adding an additional 0.03cc and see what happens.

[rsterne]

Admittedly that statement is from over a year ago, during development of the prototype.... However, the point I was trying to make is that as you make the chamber smaller, the valve acts more and more like a conventional valve, with the exception that you are reducing the cracking force (and only the cracking force)…. If the chamber is so short that it, or the spring, bottoms out before the valve opens, limiting the travel, then of course it is too small.... I had that occur, even though measurements said it should not, because to get usable dwell I needed a greater hammer strike, which caused the valve to open so fast that the poppet was driving the stem past it's normal lift and bouncing off the coil bound spring and slamming shut again.... I actually destroyed one poppet from that internal collision, even though the hammer struck the back of the valve body before the poppet spring went coil bind.... It looked from the damage to the poppet like the hammer was driving the poppet into the spring, but that was impossible, the poppet was accelerating into coil bind with the spring as it "blew open"....

Sometimes it is difficult to separate one effect from another and come to the wrong conclusion.... Other times, the conclusion was, indeed wrong.... Just like the quote from George Bernard Shaw....

"All generalizations are false.... including this one".... 

Here is another generalization that I feel applies to the simplified balanced valve.... The larger the balance chamber, and the smaller the vent, the more tendency for the valve to "blow open" once cracked.... This reduces the hammer strike required to produce a given dwell, but tends to make the valve almost impossible to tune, it either cycles or it doesn't.... developing a "plateau and cliff" like the Cothran valve.... The point of reducing the balance chamber volume (and increasing the vent size) is to avoid that situation....

Bob

[Scotchmo]

...
Here is another generalization that I feel applies to the simplified balanced valve.... The larger the balance chamber, and the smaller the vent, the more tendency for the valve to "blow open" once cracked.... This reduces the hammer strike required to produce a given dwell, but tends to make the valve almost impossible to tune, it either cycles or it doesn't....

That might be what I'm getting. It either cycles or it doesn't. Because of the light hammer and short stroke, I might be relying on the "blow open" for it to work. I'm not yet convinced that "blow open" is necessarily a bad thing, as long as it closes when I want. OK - I'll work on it some more.

[MJP]

Blow open is good at least it has worked for me in all my guns. You tune the closing with the port and not with the hammer strike. You use the lightest possible hammer and spring that can consistently open the valve.

No point in searching for a curve where it is not needed. Tuning the chamber venting gives you your dwell and you get max flow from the valve as it blows wide open.

Want a shorter dwell make a larger vent port.
Or better yet make the vent size adjustable.

Marko

[PikeP]

Balance chamber fill time / flow rate of air into a balance chamber is determined by pressure, altitude, temperature, vent length, and most importantly, Vent OD.

Timing this event to get a desired closure event similar to a conventional valve, yet all the benefits of a balanced valve with reduced cracking/opening forces (resulting in ONLY less hammer strike, nothing more), requires both a properly sized vent OD and balance chamber volume. One can simply just throw in the smallest possible chamber that will allow full lift, and the largest vent od that doesn't compromise their poppets structural integrity, but they will simply not obtain the ideal chamber volume fill time that provides maximum benefits of a 'hybrid-semi balanced valve', unless the stars and planets align just right for them...

The goal to be able to tune with hammer strike with a hybrid valve solely relies on timing this event correctly to achieve maximum tune-ability for YOUR desires. One can setup this valve to have hammer spring adjustment resulting in a variance of 600 fps, where as another can set up this valve to have a variance of 20 FPS, or anywhere in between the two. Depending on the application, your needs may vary, as so will your required vent od / chamber volume ratios.

I showed this much earlier in the thread using flow rate formulas while we settled on ideal fill times to achieve proper tune-able ranges in Bob's build, and its tried and proven, I have no doubt he's content with the range of dwell he can manipulate with hammer strike, those ratios are for his application.

Its a VERY delicate process when it comes to timing the transitional event of going from semi-balanced to non-balanced...

The formula required to obtain the approximate ideal ratios require a lot of data, the formulas are not simple, nor overly complex. It requires calculating flow rate through a static port, so that the balanced chambers volume is filled within .5 ms - 3ms...the desired fill time (in ms) is dependent primarily on your desired tuning range, AND barrel length, as valve dwell and barrel length are directly tied together...

In summary...

fill balance chamber too fast, lose some benefit of a balance valve and their reduced hammer strike requirements, wider range of fps / valve dwell with hammer strike, which can exceed whats desired per application.

fill balance chamber too slow, retain benefits of balanced valve through-out shot cycle, less hammer strike needed, severely limited or no range of fps / valve dwell from hammer strikes.

fill chamber at the right time...achieve maximum benefit of both a balanced valve and conventional valve, which means greatly reduced hammer strike required to operate the valve, and a tune-able range that fits within an applications needs, be it 200 fps, or 600 fps...

[MJP]

Altitude plays no significant role in valve timing, port and valve vent is not at atmospheric pressure when the valve opens, it has no meaning what altitude you fire that 300bar from the reservoir.
I'm not interested in any conventional valve behavior, but that's just me.

Marko

[Scotchmo]

...
The formula required to obtain the approximate ideal ratios require a lot of data, the formulas are not simple, nor overly complex. It requires calculating flow rate through a static port, so that the balanced chambers volume is filled within .5 ms - 3ms...the desired fill time (in ms) is dependent primarily on your desired tuning range, AND barrel length, as valve dwell and barrel length are directly tied together...

In summary...

fill balance chamber too fast, lose some benefit of a balance valve and their reduced hammer strike requirements, wider range of fps / valve dwell with hammer strike, which can exceed whats desired per application.

fill balance chamber too slow, retain benefits of balanced valve through-out shot cycle, less hammer strike needed, severely limited or no range of fps / valve dwell from hammer strikes.

fill chamber at the right time...achieve maximum benefit of both a balanced valve and conventional valve, which means greatly reduced hammer strike required to operate the valve, and a tune-able range that fits within an applications needs, be it 200 fps, or 600 fps...

Best I can calculate (choked flow through a static port), the no go fill rate for my balance chamber was about 0.2ms. At 0.3ms-0.4ms, the valve opened somewhat reliably. Enlarging it further (0.6ms) did not seem to make a measurable difference in projectile velocity. Maybe I would need >1ms to notice any dwell increases from the balance chamber.

What I'm learning -

1) For a balanced valve that cracks only, use standard tuning of the striker mass/momentum/energy to control dwell (and FPE for a given projectile).

2) this is where we actually are for most "balanced valves" - somewhere between (1) and (3)

3) For a balanced valve that blows fully open, use chamber fill rate to control dwell (and FPE for a given projectile).

Or maybe we could leave the dwell constant and just vary the fill pressure. That won't work with a conventional valve (heavy mass striker) as dwell varies greatly with pressure. But for a blow open valve, velocity should be mostly proportional to pressure, without any other tuning.

Note:
you said: "Balance chamber fill time / flow rate of air into a balance chamber is determined by pressure, altitude, temperature, vent length, and most importantly, Vent OD."

The balance chamber is filled by the plenum air at high pressure, so I don't see how altitude would matter. Vent length should make little difference as long as the minor diameter of the vent is at the balance chamber. The approximate fill time of the balance chamber could be as simple as this:

balance-volume/(vent-area x SOS)

[Brian W Cook]

If you build the front of your valve so the air flows over the poppet head there won’t be any of the “blowing open “ going on .   You can even vent your chamber to the atmosphere and it will still work just fine

[Jenny domansky]

I've got a melon scratcher that frustrating me. .I'm building 3 mrods ...1 with a war cobra valve ,just put it together and perfect.
The 2 others are using Jefferson state ss valve, built them, started to gas and on both the air runs straight through and out the barrel, what is happening tried using the port with the o rings and without....HELP PLEASE

[rsterne]

My guess is that your hammer spring is holding the valve open.... Try cocking the gun before filling.... Once you have air pressure in the reservoir it should be OK.... but you may need a lighter hammer spring so as to not waste a lot of air....

Bob

[Motorhead]

If Bobs suggestion does not work ? ... May need to spin the valve stem in a drill with a bit of pull back pressure to burnish in the seat.

[Scotchmo]

My guess is that your hammer spring is holding the valve open.... Try cocking the gun before filling.... Once you have air pressure in the reservoir it should be OK.... but you may need a lighter hammer spring so as to not waste a lot of air....

Bob

+1
When filling my Skyhawk, if there is any air pressure in the tank, I don't need to cock it to fill up. But when totally empty, I often need to cock it to relieve the hammer spring pressure from the valve stem.