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PostPosted: Mon Oct 27, 2014 3:30 pm 
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Joined: Wed Nov 10, 2010 3:09 am
Posts: 11
Location: Victoria BC
Hello All,

Background: I am designing a non PAL PCP (winter project) with compact integrated valve body, breech (for magazine), regulator.
Goal: Have a pressure regulator that is "stable" regardless of input pressure. Its not a rapid fire paint ball application, fill rate can be sacrificed for control.
I need: To prod the brains of folks that more than just shimmed for average regulator output pressure, but understand regulator "tuning" and/or any subtle modes of operation.
See drawing: Concept only. Unrefined configuration lacking valve spring, piston stop, shims properly engineered threads, burst discs blah blah etc.
Whats in it for you: I will share all my drawings AND release all solid models when I am done (this will take a while, life , work and all that).

Questions:
1) Piston has a large input/output diameter ratio, so input pressure variance has diminished effect on output. Do you concur with this principal?
2) I am aiming for a spring stack of high load but low spring rate (low change in force vs distance) disc springs. Is there any downside to using low spring rate to achiever fine control?
3) What is the high pressure valve seal (the small one that regs pressure) material for a typical ninja type reg. I do not want to pay $90 just to disassemble, look then bin it. I am tending towards delrin or peek or is it more like 60A or 90A durometer urethane. Thoughts?
4) Am I missing anything?
5) Should I join another forum to ask these questions (rather not).

Thanks,
Mark


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PostPosted: Mon Oct 27, 2014 7:48 pm 
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Joined: Mon Sep 05, 2005 10:55 pm
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Location: Rocky Mtn Hse Alberta
Make piston bore part of blue reg body
Vent spring case.

Beautiful cad drawing there.

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PostPosted: Tue Oct 28, 2014 8:01 am 
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Looks fascinating - can't wait to see it develop!

What calibre are you thinking of using? You said non-pal which made me think low power because I tend to think in terms of .177, but if you were thinking big-bore it would be a different kettle of fish. I'd love to make a regulated low power 177, so I'm especially interested in how this goes :)

I wonder what the ideal volume for the low pressure plenum is. My guess is that bigger is better from a shot consistency point of view, but a larger plenum cuts into the space for the high side reservoir.

Jim


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PostPosted: Tue Oct 28, 2014 4:15 pm 
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Location: Coalmont BC
I don't see provision for a Plenum in that design, the valve poppet is right inside the low pressure chamber.... The rule of thumb of 1cc per FPE of volume on the LP side still applies.... You can get away with less volume, but be prepared to run a higher setpoint pressure to make up for the pressure loss during the shot.... Mind you, in a non-PAL application it may not matter, you're only dealing with 4 FPE in .177 and 7 FPE in .22 cal.... so you don't need a lot of volume....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Oct 28, 2014 5:31 pm 
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Location: Victoria BC
Hi Walter,
Yes the vent hole is missing (but not forgotten) from the sketch. If the piston is inside the blue body it gets smaller and more like a paintball reg. If an "authority" would offer up a list of compelling reasons not to, I was going to pursue the large(est) piston size differential for this project to learn something. Easy to revert to something more conventional as you suggest if results are poor.

Hi Jim,
I want accuracy, so a choked barrel. The only source in Canada that I know of is from Eric at S&A and its a LW .177 by 12mm O.D. (prefer a 14 or 15), so that may steer the project, if there are other barrels around I would like to know. A LW barrel is $$$ unfortunately, may use a crosman instead and choke it myself. RE Low pressure chamber, for a .177 is excessive, however just because we have a lot of volume does not mean we have to use it all, but just in case... I have a POL so a non PAL rifle for now. The ultimate end is to have a microprocessor solenoid controlled hammer like a Daystate. Their chamber volume is about the same size. Iteration 1 will be conventional hammer with a QB trigger assy from Eric. Iteration 2 will let me dial up anything :D

Hi Bob,
Thanks for the pointers and numbers. For my education and understanding (airgun "design" rookie) may I have a bit of clarification:
* Please refer to the 1377 valve (spring missing from view), which part is the "plenum". A, B, C, D, other?
* I have a large low pressure (LP) chamber. Why might I have a higher set point if when the poppet opens there is a large volume of air that diminishes pressure at a lower rate than a small chamber. My thought was to use a lighter hammer, springs etc to open the valve (goal, less hammer bounce) for a shorter time and conserve the remaining pressurized air in the chamber for the next shot (sort of a secondary LP "tank").

The large LP chamber is more a function of my follow through of the machining operation for the piston and the reservation of space for the poppet spring. I could perhaps have the poppet spring nested inside the piston, its force would be a low order effect on the entire operation and would not affect the set point much. That would be a way to reduce the chamber some. Hmmm

Posted a JPG of the basic profile (subject to drastic change). Note this breech is not tall like a typical marauder magazine breech, also there is no thin spot usual retrofits have, so the scope should be happy on a very stiff base. Most of all do not have to rely on that darn single little 4-48 screw that crosman uses to attach the breech on the ubiquitous 2250 (original intended donor gun). Oh and a floating barrel so changes in pressure on the tank do not telegraph through a barrel band to the barrel and affect aim. The project is going to stall for a little while as there is a lot of number crunching to do on the thread design (read I don't want to die... yet).

Anyone out there have at least an idea if a HPA reg high pressure seal is much harder, compared to say a tire?

Thanks all, Mark


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breech2.JPG
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1377 valv ass.JPG
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PostPosted: Tue Oct 28, 2014 5:46 pm 
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I think the plenum is C + D in that diagram. In a 1377 valve it's all the volume of pressurized air readily available to exit when the valve is opened. (The spring for the two valves is missing and that subtracts from the available volume of course).

Sounds like you're going to have a huge amount of fun. I'd thought about a solenoid for the hammer too, but if I was doing that I'd really like to go unregulated with a pressure transducer and a microcontroller to compensate for the varying input pressure. I think that should have some advantages in terms of overall efficiency. Another thought that won't go away is an electronic valve - I wonder if an automotive direct injection valve could be used. The reliance on batteries would be a nuisance, but the software/control side of it would just be great fun :)


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PostPosted: Tue Oct 28, 2014 6:00 pm 
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Joined: Mon Sep 05, 2005 10:55 pm
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Location: Rocky Mtn Hse Alberta
Go for it.
Firing volume needs to be tailored to the power output so as to deplete the regulated air enough that the reg opens. If that fails to occur you may see cycles of velocity variations.

Make a step in your receiver to keep the piston from popping out of place when filling.

BTW what is your background? Who will machine these bits?
Looking forward to seeing this come together :-)

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PostPosted: Tue Oct 28, 2014 8:08 pm 
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B, C, & D together are the internal valve volume, plenum, and reservoir (call it what you want) in a pump and dump valve.... they contain all the air you can ever have for a shot, which is similar to your valve.... Are you planning on running a dump valve where the valve is still open when the pellet leaves the barrel?.... OH! on reading further, you are not, you plan on conserving some of the air in the LP chamber, which is a good thing, much higher efficiency than a dump valve....

In an unregulated PCP, you have the valve and the reservoir, and if the air can flow freely into the valve, then the air in the reservoir is available to maintain the pressure inside the valve during the shot.... In a regulated PCP, the regulator separates the valve from the reservoir, just as does the check valve in a pumper.... The regulator can't act fast enough to top up the valve during the shot, so the pressure drops very quickly compared to in an unregulated PCP.... A plenum is a space between the valve and the regulator with enough volume that it maintains a higher pressure inside the valve during the shot.... A volume of about 1cc per FPE that the gun produces will keep the pressure inside the valve within about 10% of what it was in the unregulated PCP.... As you decrease the volume downstream of the regulator, you get a greater and greater pressure drop during the shot, which obviously reduces the power compared to what you would have with a larger plenum at the same pressure....

In your application, non-PAL, you are comparing your volume to that of a 1377, and indeed yours looks larger.... Compared to the 215 cc reservoir in an MRod, however, it is tiny.... If your unregulated MRod could produce 500 fps on only 500 psi (which is likely) then if you have enough plenum (LP) volume you can run the regulator that low.... If the volume is the same as in a 1377, then you will have to run it at maybe 1000 psi.... The larger the plenum, the lower you can run the regulator setpoint and still get your desired 500 fps.... However, like Voltar1 says, if the volume is too small, the regulator may not function on every shot, so you need to find a balance....

I say try it and see.... it will probably work just fine and give you tons of shots.... and fun....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Oct 30, 2014 1:01 am 
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Joined: Wed Nov 10, 2010 3:09 am
Posts: 11
Location: Victoria BC
Thanks all for the knowledge,

Jim,
I agree the ideal situation for an electric hammer system is no pressure reg. But... My half hearted search for a high pressure small pressure transducer is a fail and commercial items are too big and $$$. I have an idea of using a "cheap" strain guage (indirectly measure pressure by measuring material deflection due to stress on say a pressure vessel) but I want to start conventional before going high tech. KISS, walk before you run... The daystate pressure transducer likely would be $$$$ to purchase, I want a design on the cheap so anybody can copy it, eventually.

Walter,
Interesting "velocity variations" due to regulated pressure phenomenon, I learned something :idea: I am reasonably confident that the reg I propose should be much less sensitive to that. The ratio between HP seal diameter and piston on my design is about 28:1, a ninja Pro-v2 reg has a ratio of about 11:1 and others between 9:1 - 3:1 . I would debate that as the ratio gets smaller, stickiness in the seals, spring pack, o-rings, misc friction can become more significant. Especially (in my opinion) if the disc springs are high spring rate (seat pressure varies considerably over small travel).
RE background, official job title: Research assistant (benign I admit). What say business card: Mechanical designer/draftsman. What do I do: design equipment, and build (small prototypes) for particle physicists. Jobs: currently, design and make a graphite frame to hold a 8micron graphite foil tight and ├╝ber flat, some other tasks: design a support and manipulation "frame" for servicing a 190ton detector (its 150m down, in a clean room, hard to access and just a wee tad radioactive, ok REAL radioactive) and other misc shtuff. The opening sequence you see in Divinci Code... Thats my baby (a small but important % just the same). That movie opening: total Hollywood bovine turd. If you want some atoms smashed, I can pull some strings; send self addressed envelope with said atoms and I will for a small fee mail back the remaining debris. If you want more that a couple dozen smashed it'll cost extra. RE who will build it: looks like me.

Bob,
Your explanation and numbers gives me more to chew on. I may contemplate some geometry mods, my plenum now is 4.5cc. My reg as sketched will be slow, however I will give it a "shot" for now. This reg will not flow fast then the rate of chamber filling during a shot is a low order variable from full tank to "empty" (so ~ consistent). I may have to run a higher set point as you mentioned a while ago, I get it now :idea:

FYI: a picture of a Daystate cut away that my proposed design is modeled after. The res tube is 1.25" with .094" wall that I can reasonably scale from a few other pics in my possession. My design will be hammer, but will have the internal space to go solenoid in the distant future.

Cheers, Mark


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File comment: Daystate cross section... design baseline.
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PostPosted: Thu Oct 30, 2014 8:36 am 
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Quick guess, it that Daystate tube is 1.25" OD x 0.095" the valve plenum is about 10cc.... Judging by the port sizes I'm guessing that is a 12 FPE UK rifle, so that's pretty close.... The volume is really only a concern if you decide to go non-PAL at a later date.... I am not aware of any airgun regulator that will cycle fast enough to provide any significant pressure top-up during the 1-2 mSec. that the valve is open....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Oct 30, 2014 1:26 pm 
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Joined: Wed Nov 10, 2010 3:09 am
Posts: 11
Location: Victoria BC
Hi Bob,

Oops late night, faulty numbers. My plenum as sketched 9.5cc and the unknown daystate model is around 11.7cc . Its a poor jpg to measure detail... Transfer port size is about 3.4ish mm and the valve stem about 3.3ish mm (1/8"?), throat 5.8ish mm. Set point, unknown. FPE of their rifles is set by (encrypted) software. Some no reg variants also use a built in chrony (not used on the cut away model posted). Nice rifles, but $$$$. I am too crappy a shot now to justify that outlay, besides this design exercise is positive mental stimulus that is way more rewarding than a reality show. I'd call it "projectile therapy".

Thanks


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