Making a pcp valve that has a greater than 50% "theory" max power.



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Offline Motorhead

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #40 on: October 17, 2018, 11:47:49 PM »
To be serious Bob. What your missing is that I am trying and your not. I like the "it ain't gonna work" thing but jezz, come on. Put some of your experience into it. Damnnn.

MJP,
Thank you for for the push and bread crumbs.

I have learned alot lately doing this (money work and play time work).

V2 was made today but darn, I really need a mill.

Please keep in mind, that a marauder tube or any crosman tube has a double o ring gauge port right before the valve on the HPA side for venting to atmosphere.
Not only that, I don't see an SS valve venting to atmosphere and yet people claim it reduces cocking cracking force. Tell me how that works ?

To me,
I can buy a cothran valve, Cobra valve, or SS valve but, it's just like you guys said, it's how big you can open the valve and still crack it open. I'd rather figure how out to do that instead of buying and possibly change a few things.

Please feed the ideas. This seems to be my only hobby besides work and family.

V2 is now enclosed in the valve body and uses the valve cap as a retainer.

Sort of lost ... this picture posted within a "Cobra" valve mod post made earlier in the week is a good example of the intake path your now exploring.
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Offline MJP

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #41 on: October 18, 2018, 01:40:05 AM »
Nice testing Rob, interesting idea.
Tim, it's is not stealing if you vent it to atmo. If you want balancing you need pressure difference and a best way to achieve this is a port to transfer.

Do you think Cothran was the first inventor for that design? Think past the airgun, and in to the era of steam power, its all in there,  valves, nozzles.
To make your own version of something old is not stealing its progress.

Everyone just uses what works, pressure differential or pressure equilibrium.
You can use pressure against pressure with surface area difference also.
But no matter how you do it one part of the balancing piston is always vented to atmosphere, always!

Marko
« Last Edit: October 18, 2018, 01:46:11 AM by MJP »
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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #42 on: October 18, 2018, 05:27:52 PM »
I felt bad/sad all day today because I lashed out to Bob :'( I couldn't be anymore serious. Sorry Bob. I get out of control sometimes. I would pull a force hug on him even though I know he wouldn't like it  :D.

Let's talk about V3 now. I took tomorrow off to mess around in the garage  ;D ;D ;D.

Venting to atmosphere is the quest. The question is, do we really need to vent to atmosphere or do we just need a controlled pressure difference like Marko commented?

I am thinking, a controlled pressure difference. Take my V2 and remove the hole/cross drilled hole but leave the O ring on the piston. Increase the "balancing" chamber to 3 times the max lift ( .02"*3).

Now when the gun is charged the outer diameter see's high pressure but the "balancing" chamber is at atmospheric pressure in the closed state. When the poppet opens, it compresses the low pressure air in the balancing chamber.

As long as the high pressure air get's into the low pressure chamber, we are back to balancing.

Right ?

I got all day tomorrow to turn out parts and that's the plan. Just looking for the head nods.



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Offline MJP

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #43 on: October 19, 2018, 03:11:08 AM »
Tim,
Calculate the force acting on the poppet when it is open.
You have tank pressure around the poppet, and atmosphere equivalent pressure inside the balancing chamber of yours.
How much is the closing force?

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #44 on: October 19, 2018, 05:14:26 AM »
I will tell you Shorty that best not happen again sir.  David
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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #45 on: October 19, 2018, 10:57:52 AM »
I'll try not to David.

I tried some math out and things are making more and more sense. No way can I share the spreadsheet as it is noisy as can be.

I used P1xV1=P2xV2 to calculate balancing chamber volume,pressure and poppet,piston square inch X pressure to get balancing delta.

Interesting to me was at rest in the balancing chamber without venting (just atmospheric pressure) was half the cracking force. Although just moving the poppet .02" (nearly full open) in a .075" balancing chamber resulted in a higher pressure in the balancing chamber making the closing force more.

It seems like changing the balancing volume (in this closed system) has a huge impact on pressure increase when the poppet opens. When thinking about the design of the piston, I think it may be able to be adjustable by using shims at the valve cap retainer.

Math ain't my best so here's what it looks like for cracking/closing force and a scale diagram of poppet at rest and poppet opened to .02"

« Last Edit: October 19, 2018, 11:00:19 AM by shorty »
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Offline rsterne

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #46 on: October 19, 2018, 02:04:06 PM »
Just trying to help you here, Tim.... take it or leave it....  ;)

As drawn, with atmospheric pressure inside the balancing chamber, once the valve is cracked off the seat, the poppet is surrounded by HPA.... That air pressure is trying to close the valve by pushing on the area of the valve stem.... but holding it open by pushing in the opposite direction on the area of the poppet inside the balancing chamber.... The net force will hold the valve open until the reservoir is empty, unless you have a spring to close it.... You have created a dump valve....

Balanced valves require venting to atmosphere of the balance chamber when closed to get the balancing force required.... Once they are open, and the poppet head has HPA on the outlet side (in the exhaust port), the balance chamber must rise in pressure or the valve will remain open until the reservoir is empty (unless you introduce some other element, such as a spring, to close it)…. The Cothran valve is vented through the stem (with a "leaky check valve" inside it).... The SS valve is vented through the poppet, beside the stem.... Both are vented to the exhaust port, which is at atmospheric pressure when closed, but at high pressure when open.... The balanced valve originally designed by Lloyd, and the one in the Slayer, also use venting.... This is a necessary part of the designs, and the vent diameter is CRITICAL to proper operation.... As an example, in my own versions of the SS valve I ended up with a 1/32" vent hole through the poppet, from the exhaust side to the balance chamber.... 0.020" was too small, and 0.040" was too large....

Incidently, just like regulators need venting of the area between the O-rings (where the Bellevilles are), to provide a constant reference pressure (atmospheric), your balance chamber will need something similar.... Assembling the poppet with atmospheric pressure inside and expecting it to hold that pressure, while surrounded by HPA at thousands of PSI is almost an impossible task.... Even the permeability of the O-rings will eventually allow the pressure in the balance chamber to creep up, and change the balancing force.... Of course with that area vented to the exhaust port area, that is not an issue....

Thanks for the apology, and good luck with V4....  ;)

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Offline MJP

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #47 on: October 19, 2018, 04:37:02 PM »
Tim, you can forget the volume on your calculations, just pressure against surface area.
Think about why something works, why is it made like this, then how can it be made better and not just blindly making something with some dimensions.

The envelope where it works and where it won't is very thin, and by guessing you need be very lucky.  ;)

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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #48 on: October 19, 2018, 09:00:29 PM »
Thanks for posting again Bob and accepting my apology.  ;)

Your last post and Marco's last post was the most helpful with getting a better understanding. Please keep fueling me. :D

I am starting to loose the interest in balancing on the HPA side but still working at it.

Today ( my play day off from work - and not doing any honey do lists - yes I got the stink eye from the wife), involved going to the hardware store for some supplies to build a low pressure valve test rig. It ain't pretty because my through hole on may lathe is too small so I used a hacksaw.
It will only be a low pressure test rig and figured it would be better to do this than test on the gun.

I learned exactly what you mentioned Bob. I charged the test rig to 50 psi
Test 1 : Standard poppet - opened the valve with finger force and the poppet closed as normal.
A) Opened poppet a little and it closed normal and fast
B) Opened poppet so valve stem is flush with back of valve and poppet closed as normal fast.

Test 2: V3 without oring
A) Opened poppet a little and it closed normal and fast - felt like the same force as test 1
B)  Opened poppet to max distance on the piston ( covering the cross hole ) and valve stayed open and dumped.

It's time to think a few things over now.

I thought it was interesting that V3 operated normal until the piston sleeve covered the cross hole and dumped. I was not expecting that.
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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #49 on: October 21, 2018, 09:05:17 PM »
No metal turning this weekend but alot of thought. You guys are right, there's just now way around not venting. It's just what's the easiest way to vent.

I think I have V8 that vents through poppet and added a secondary piston rod that rides in the center of the main piston. I would think that the inside piston uses the HPA to close the valve and possibly allow the valve to generate a bell curve.

That small piston/shaft would be way too hard for me to manufacture so I found these RC shock shafts with o rings (3mm/.118" diameter).
https://www.amazon.com/Team-Associated-91488-Shock-3x21mm/dp/B00J9F9YDQ/ref=zg_bs_6925937011_13?_encoding=UTF8&psc=1&refRID=5EPNJ8JDQMH1JB17W8XB

I am also looking at the bulldog valve housing and poppet to use as an insert in the mrod valve body. Not sure if I can get it to fit, but it sure would be nice. Still trying to get dimensions on it.
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Offline oldpro

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #50 on: October 22, 2018, 05:53:16 PM »
No metal turning this weekend but alot of thought. You guys are right, there's just now way around not venting. It's just what's the easiest way to vent.

I think I have V8 that vents through poppet and added a secondary piston rod that rides in the center of the main piston. I would think that the inside piston uses the HPA to close the valve and possibly allow the valve to generate a bell curve.

That small piston/shaft would be way too hard for me to manufacture so I found these RC shock shafts with o rings (3mm/.118" diameter).
https://www.amazon.com/Team-Associated-91488-Shock-3x21mm/dp/B00J9F9YDQ/ref=zg_bs_6925937011_13?_encoding=UTF8&psc=1&refRID=5EPNJ8JDQMH1JB17W8XB

I am also looking at the bulldog valve housing and poppet to use as an insert in the mrod valve body. Not sure if I can get it to fit, but it sure would be nice. Still trying to get dimensions on it.

 This is almost exactly how I built the original SS valve I will dig up pics of it from my hard drive, it worked ok but not nearly as well as current version.
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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #51 on: October 23, 2018, 05:39:10 PM »
I kind of thought the V8 version was similar to how the SS is set up.

And,

This post (to me) is for something different/new.

So,
With all that I am learning, I need to go in a different direction on the balancing and closing.

I tell you though, the test jig is fun. I am using a modified charpy test to understand cracking force and how far the valve opens (low pressure of course). I keep thinking to myself it would be nice to put something on the exhaust port to measure pressure and volume when the valve opens.

Cool thing was, the neighbor was throwing out a small compressor because he got a new one. I picked it up and it works great for this science project.Free.

I have been considering getting a "ball turning" tool for the lathe. You know, for the poppet geometry. The more I think about the poppet geometry, the more it makes sense to have some sort of "tailing" end to it in the throat.

As a thought, I am curious to know if a floating poppet (sliding on the valve stem) may be considered in a hybrid pilot "style".

More thoughts coming and hope others have more input.
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Offline Hobbyman2007

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #52 on: October 23, 2018, 09:14:16 PM »
After “ tuning “ a BT65 in .25 cal  to way beyond what it was designed for (140+ FPE) and the parts started failing . I knew making big power from a relatively tame platform was a poor choice , this lead me to the Winchester project.  I believe that having a pressure loss behind the projectile is the reason for the lack of “theoretical maximum “ achievements . With an infinite supply of air that remains at  the same pressure  from start to end of the barrel will gain the biggest FPE , kinda like why helium makes the power it does . I’ll be trying Marcos overporting technique on another project in .177 cal . Still looking for a few parts before that gets on the bench . Thinking a 24” barrel behind a Cothran valve with .25 porting . Come to think of it I already have all the parts , I got to go .....
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Offline Bill G

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #53 on: October 25, 2018, 10:27:27 AM »
After “ tuning “ a BT65 in .25 cal  to way beyond what it was designed for (140+ FPE) and the parts started failing . I knew making big power from a relatively tame platform was a poor choice , this lead me to the Winchester project.  I believe that having a pressure loss behind the projectile is the reason for the lack of “theoretical maximum “ achievements . With an infinite supply of air that remains at  the same pressure  from start to end of the barrel will gain the biggest FPE , kinda like why helium makes the power it does . I’ll be trying Marcos overporting technique on another project in .177 cal . Still looking for a few parts before that gets on the bench . Thinking a 24” barrel behind a Cothran valve with .25 porting . Come to think of it I already have all the parts , I got to go .....
Your discription of keeping pressure not deviating for the entire length of the barrel would waste huge amounts of air. I understand your approach to the theory. Imagine the instant the poppet opens, you essentially add the volume of porting and barrel to the reservior. So pressure could not remain the same. Maybe I missed the idea or you were just hypothesizing no loss of pressure. In acuallity, the air would act more like a spring. Imagine the spring can only be the length of the barrel. This spring has to move it's own mass as well as the projectile. The longer the valve is open the later the the spring is delayed to decompress. Now imagine that any portion of the spring extending out side the barrle is on no use. So, yes the valve open longer does keep pressure higher on average but will also allow more of the spring to be outside the barrel, which is a big loss of efficiency.  Bob has published extensive data on this. As I recall, not much over 1/3 the length of the barrel is likely optimal. As to helium, it is much lighter than air so less of the stored energy is used to push itself. This is quite a bit of energy now applied to projectile.
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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #54 on: November 11, 2018, 03:06:56 PM »
I broke the 50% mark today. I hit a 64.8% max power level.

It wasn't at a high pressure though. It was at 500 psi fill pressure.

26.5 FPE at 685.5 FPS using 25.39's 20" barrel.

I know this may not mean much to others but it sure has peaked my interest again. I would guess that there was little to no loss of energy with the hammer to valve stem collision and the poppet dwell was long due to low pressures closing it.

That's the only explanation I can think of.

The only reason for messing around with the very low pressure stuff is that my buddy hooked me up with some C02 fittings and i wanted to see what the gun can do at 800 psi.

Anyhoo,
I have it in my head now that reducing the loss of hammer energy to valve stem collision so that the valve can open fully along with an extended dwell is paramount to getting over a 50% max power level.

Making a system that generates 50% over the "max fpe theory" appears to be the complete opposite of what I have been doing on my airguns for the past years.

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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #55 on: November 11, 2018, 03:18:22 PM »
Forgot to mention that the spreadsheet that I use to calculate "estimated" power level appears to by way off when running below 1000psi.

At 500 psi my calculator says I should have only done 16 fpe but, I got just over 26 fpe.

My spread sheet only uses the force behind the pellet with a "historical" (fudge factor number). It works great at pressures above 1000 psi but I guess there's alot missing from it to be accurate for all the other things going on in the system.
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Offline MJP

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #56 on: November 11, 2018, 03:38:19 PM »
Nice one Tim!

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #57 on: November 11, 2018, 06:02:55 PM »
Interesting results.... What kind of gauge are you using?.... Digital or ?? ??

There would be only about 10 gr. mass to a barrel full of air at such a low pressure, which could explain your results.... More for us to learn, that's for sure....

Bob
« Last Edit: November 11, 2018, 06:07:27 PM by rsterne »
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Offline shorty

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #58 on: November 14, 2018, 05:38:30 PM »
Ran a test today to try and understand if it's the lift or the dwell that is creating the "over 50% mark".

I have my hammer spring cap drilled and taped to 1/2" 20 so I can back it out all the way. And with the 500psi shots, it's all the way out.

I ran some 43.2 eujins starting at just over 500 psi ( hovering around 650/700) and got 560fps (30fpe) down to 495psi ( 23.5fpe) "very much in the red" and confirmed on a different gauge to be hovering around 425 PSI when ending.

I recharged the gun just like the above and gave it 2 turns on the hammer spring adjuster. Velocity went down to 450/425 fps. I think the hammer was bouncing off the back of the valve creating less dwell.

So,
I think, dwell may be the answer to over the 50% mark. Problem is, how do you control dwell besides hammer mass and HPA on the poppet ? It's for sure micro seconds of dwell that makes the huge change.

Who knows, maybe it's at easy as over lifting to generate the dwell (adjustable valve stem length)
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Offline Hobbyman2007

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Re: Making a pcp valve that has a greater than 50% "theory" max power.
« Reply #59 on: November 16, 2018, 07:45:23 PM »
Shorty, I think getting the most amount of air to the back of the projectile as fast as possible is the answer. There are several ways to do that . All of the methods I’ve tried require huge hammer mass or low pressure . That is unless you use a ballanced valve . This is only my opinion and have no actual math to back my findings . I have yet to build something with overbore porting ,but it is coming soon .
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