Simplified Balanced Valve

[PikeP]

Makes sense I'll update my sheet accordingly to that. I was going the other way with ratios

[PikeP]

Fixed...here is the updated sheet.

[rsterne]

I think we have determined that a 70% reduction in the force (ie 84% of the diameter) will not work.... In my SS valves (which work the other way, the smaller the front portion, the larger the reduction) I ended up using 2/3 - 3/4 the diameter.... Travis uses 80% of the diameter for the front portion.... With this design I think 1/2 the force (70% of the diameter) is the biggest you can go.... Travis is talking about using 56% of the diameter.... We don't know yet, but I think those may be the outer limits of the range.... That would mean for my valve, with a 7/16" poppet, the front end would be 1/4" - 5/16"....

Bob

[rsterne]

Those look right.... Can you please do my current valve, with a 1/8" stem and a 0.040" vent, 1" long, and increase the height of the balance chamber to 1/4", hammer travel to 1", hammer weight to 77 gr., hammer spring rate is 11 lb/in.... Then change the vent to 0.047".... Then the stem to 0.156".... Then the vent to 0.063".... Those 4 models should be all I need (I hope)….

Thanks....

Bob

[PikeP]

I think what we are ultimately trying to achieve is a hybrid valve that starts off balanced and quickly returns to conventional functions ideally around peak lift. Whatever parameters give that outcome will likely require hammer energy right in between that of a fully balanced and conventional valve. Hopefully these valves become standard use for big bores with tunable range and a healthy amount of reduced force to operate the valve. I think vent sizing, chamber volume, force reduction %, and valve stem od are all critical in getting this design perfected and operable across many calibers. Hopefully we can dial in a spreadsheet to represent at least what we're experiencing which may allow exploring more ways to skin this cat being there are 4 very favorable variables in action here.

[rsterne]

I think what we are ultimately trying to achieve is a hybrid valve that starts off balanced and quickly returns to conventional functions ideally around peak lift.

I agree 100% with that assessment.... My stated goal in the first post was a significant reduction in hammer strike, along with tunablity…. combined with minimum parts and easy to machine.... The devil is definitely in the details.... I also think that once the correct proportions are determined, the valve should be scalable....

Bob

[PikeP]

Here are the 4 models you requested Bob.

Added a 5th to fill some gap.

[rsterne]

That is brilliant, Mike.... Thanks so very much.... This is fun stuff, eh?....

I think it is pretty obvious what I need to do.... I need to first drill the vent in my existing stem to 0.047".... While I have it out, I may just be able to drill everything out to 0.052" (the next number drill larger than 3/64" is a #55) without breaking any drills.... I hope.... If the flow rate increases to 94 mg/ms, I should be down to about 0.93 mSec.… I won't complain if you want to add that model (1/8" stem)…. 

After that is tested, to see if it makes any difference....  ie shows any signs of being tunable.... then I need to make a new poppet with a 5/32" stem and 1/16" vent hole....  …. WOOHOO, this is exciting stuff !!!!!!!!!!!!!!!

Bob

[PikeP]

An important note and thought. The pressure chamber fill time calculation relies on throat being full pressure..would likely have to add a few micro seconds to that time for this event to fully occur..however I'm guessing its minimal but likely to raise the current figure by 15 to 20%...I could try to estimate that figure and add it into the calculation however with how marginal it is compared to fill times I may leave it out.

I think this also implies vent distance from seat is important...if your vent entered the throat during lift I'd imagine it be even better.

[PikeP]

You were correct in your assumptions with the
.052 vent and .125" stem.

[rsterne]

I don't think we need to refine things like that, that are not well understood.... The model will grow and improve with time.... These spreadsheets end up having a mind of their own, and a life of their own as well....  …. I think you have a very workable model right now.... With a bit more experimenting to set the parameters, it will likely get to the point of predicting results.... which is the ultimate goal for any model....

Thanks, I'll see if I can drill the stem out to 0.052" without breaking the drill and ruining the poppet.... 

Bob

[PikeP]

Might I suggest after you drill the vent to .052", if it's not enough...try reducing the chamber height by .05" to achieve the following. Small incremental changes seem best as you really do seem to be close based on your current efficiency and power level

Also added medium hammer weight which is scaled equally to heavy and light which predicted what Bob is currently using.

[rsterne]

I may be able to reduce the cavity height with a filler block.... We haven't allowed for the spring cavity, which adds even more volume.... I am also considering using a stronger spring....

Bob

[PikeP]

Valve spring rate would harshly effect the first 25 or 50 percent of valve opening more than chamber sizing, vent sizing or even stem od sizing as it would be a mostly static force increasing slightly with lift and the other 3 variable through shot cycle. Just my 2c!

[PikeP]

Added spring volume by mass assuming density of music wire at 7.86 g/cm3...for builds that use a spring inside the pressure chamber. Also added separate calcs for spring chamber in case dimensions vary, but can be left at 0 if not.
 
I also added optimal fill time until more things are figured out where we may be able to automatically calculate that based on parameters, also added a flow efficiency correction factor.

I also subtracted half the valve lift from pressure chamber height to determine volume as it spends the majority of the time at 50% through the valve opening event.

Feel free to request any other additions.

[MJP]

No matter if you get one size working just right, the valve won't be scalable so easily.
And making the hole in the stem vs having a straight hole in the valve face alters the behavior.
All the time you are altering the time how the balancing chamber gets filled.
You are forgetting the flow in the equations, flow over a corner creating dead space for x amount of time.
Its just not all about pressure.

Something that works on a large scale wont work on smaller one, I'm not going in to measurements because I all ready have a headache from your nonsense fractional system.
It was nice to see couple of metric dimensions but rest of it was all chinese.

Oh forgot to mention that even the location of the hole on side the stem how far it is from the valve face has an affect.

Marko

[PikeP]

I apologize for the imperial units but it's what many in north America are raised up on and accustom to.

Bob started this thread with interest in understanding what makes balanced valves tick..or not tick. The point of the model is to help find optimal dimensions and other variables. If it helps push balanced valves more into main stream I'm all for it. Every variable you speak of can be accounted for and flow losses are already one of them, not to say all are currently accounted for but I dont think it will be necessary once some blue prints are laid out...the ratios may scale just fine provided all things are scaled equally..we will certainly find out in time.

[MJP]

No need to apologize, it's just my problem that you guys have not adopted to use metric system like it was planned decades ago. 

But what comes to the scale, the simple version wont scale up without modifications. At least what I have tried didn't.

Douglas, you can get metric O1 from Europe.

Marko

[PikeP]

I agree Marko that the metric system is simpler and superior.

I think there is a scalable set of variables that will work where some key variables remain constant.

I ran a quick calculation and compressed air at 3000 psi should travel the 1.1 inches to the chamber in .06 ms...being that air is traveling roughly 17.52 RMS inches per ms at that
pressure...pretty intense. However I have now included it since it's a factor..also my flow coefficient is currently set at 95%. Could need lowering with such small orifaces but ultimately once dialed in would stay relatively equal for similar vent sizes.

[PikeP]

Some interesting math I did. To generate 270 fpe  @ 28% thermal efficiency you need to eject 3491 mg at 3000 psi. Bob's 1.17 fpe/ci shot was at at 23% thermal efficiency using roughly 18 ccs of air. Where as his 1.44 fpe/ci shot was at roughly 28% thermal efficiency and ~14 ccs...its pretty amazing when you can backwards calculate required air mass ejected for a desired energy level, it helps build a high powered rifle around that knowledge, to be able to not just set goals but more than likely meet them. I find sizing your port  to flow 10% higher than your intended fpes required air mass is best. Where a .33 port should flow 3882 mg/ms at its peak. Of course knowing a ports limitation is only a small part of the equation and only one of many questions answered out of the many that remain.