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Steve NC, and other airgun gurus.......

December 6 2017 at 7:40 PM
Phil  (Login Duane30)
YF

Question regarding the Webley Paradigm piston design/theory.

The piston in said gun has a Belleville spring stack aft of the piston seal. The seemingly functioning design works by compressing under air charge, creating headspace. Once the gun is fired, the spring stack unloads towards the valve. The logic is that the single stroke charge of air pressure is maintained by this approach, by not suddenly dropping off due to transfer port passage.

My question:

If a gun has, say, .10cu/in valve volume (including induced piston headspace) with a transfer port passage volume of .035cu/in, the piston will need to move at least an equivalent volume of .035cu/in, right?

In single strokes, as we know, stored pressure differs from that of firing pressure. The transfer port passage in a single stroke can reduce pressure significantly. The Achilles heel of SSP.

With that said, the telescopic piston made for the SSP project, but now has a fixed piston, may experiment with it. Make it function like the Paradigm to see what happens.

"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."

 
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Scot Laughlin
(Login classicalgas)
YF

Think about this...to be effective in maintaining charge pressure

December 6 2017, 9:20 PM 

the piston has to weigh less than the air charge it's pushing.Otherwise it's lagging behind the pressure drop of the charge, and not doing much good. How likely is it you can build a piston/spring system that weighs about what your pellet does?

 
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Steve in NC
(Login pneuguy)
AR&P

You're absolutely right, Scot, that the Paradigm piston competes with the pellet...

December 6 2017, 11:02 PM 

...for kinetic energy. But the reason it works anyway is because the piston only moves about 1/200th as far as the pellet, therefore has an average speed only 1/200th as fast, and so (because kinetic energy goes as the square of speed) steals only (1/200)2 = 1/40000 as much energy for every unit of mass.

So even though the piston probably weighs ~200x as much as the pellet, it nevertheless robs less than 1% of the energy.
Steve

 
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Willy
(Login willy1)
YC

Ya better get Steve in here" the wise old Owl.He's the only

December 6 2017, 10:18 PM 

scientist that i no of on any airgun forums.

 
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Steve in NC
(Login pneuguy)
AR&P

LOL! Thanks, Willy. But if you're talking about my li'l avatar pix, it's not an owl.

December 6 2017, 10:53 PM 

It's of one of the beautiful red-shouldered hawks that help me clean up after each session of rodent-snuffing.

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Steve

 
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Steve in NC
(Login pneuguy)
AR&P

FWIW, my take on how the Paradigm powerplant works is...

December 6 2017, 10:47 PM 

...mainly by taking advantage of the higher efficiency of a metal spring over a compressed air charge at giving back more of the energy invested in compression. This advantage arises from the fact that much of the work of compressing air is lost in heating the air, only to dissipate before the shot is taken, and thus wasted. Steel springs don't do that.

Consequently, by sharing the energy of the compression stroke between the air charge and a highly preloaded steel spring, more energy can be extracted from a given pump displacement volume, while simultaneously reducing the peak pressure of the charge. Hence more power from less effort: win-win.

The plot below simulates the result.

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Steve


    
This message has been edited by pneuguy on Dec 7, 2017 12:44 PM


 
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Scot Laughlin
(Login classicalgas)
YF

I completely forgot the steel vs air spring advantage, but even with the short throw

December 7 2017, 9:32 AM 

would't the piston still have to lag behind the pressure drop, since it can't move until the pressure ahead of it drops below the spring stack pressure?

 
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Steve in NC
(Login pneuguy)
AR&P

Sure. But it doesn't take much of a force imbalance/pressure differential to...

December 7 2017, 12:21 PM 

...enable the piston to keep up, considering it has >20x the frontal area and <1/100x as far to move as the pellet.
Steve

 
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robny
(Login murphy29)
YC

what about a shortened and

December 6 2017, 10:49 PM 

limited throw gas ram inside the piston assembly, sounds silly, But I cant see much else chasing the air charge. I know crosman sells them for 9 bux , and a few companies make smaller variants.The pressure could act on the face of the ram , keeping it energized and flush to piston face.. when the seal is broken , the ram chases the charged air out the Tp


    
This message has been edited by murphy29 on Dec 6, 2017 10:52 PM


 
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Steve in NC
(Login pneuguy)
AR&P

Not enough oomph. Springer springs (both gas and steel) only generate...

December 6 2017, 11:11 PM 

...a couple of 100lbs of force. A Paradigm type needs 2x or 3x as much.
Steve

 
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James Perotti
(Login jpsaxnc)
AR&P

I would want to know the closing force on the pump lever,

December 7 2017, 9:31 AM 

and the weight and velocity of the pellet, before I gave any thought to the mechanics involved.

 
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Phil
(Login Duane30)
YF

Well, using the po-man bathroom scale (digital) method...

December 7 2017, 12:43 PM 

...the weight of the gun reads about 10 pounds equipped. Pushing down on the lever to pump peaks at 51 pounds. This is giving me slightly over 600fps in 14.3 CPs. Just enough punch to take rodents out to 40 yards and more, yet nice and flat trajectory for my given shooting distances.

The springs, though not Belleville, require 500 pounds to fully compress just shy of coil bind (Chevy small block valve springs).

If all the aforementioned theory is applicable, I am chasing a fools errand. The spring and piston certainly weigh more than a pellet! Sure it may do what I think it will, but will not respond fast enough to chase the air charge out. sad.gif
"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."

 
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Steve in NC
(Login pneuguy)
AR&P

IMO, doing the Paradigm thing in your SSP with 500# springs...

December 7 2017, 1:05 PM 

...would gain you easier cocking, but probably not much added power, because the springs would stack at only 600psi or so.
Steve


    
This message has been edited by pneuguy on Dec 7, 2017 1:05 PM


 
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Phil
(Login Duane30)
YF

I suspected that be the case...

December 7 2017, 1:23 PM 

...Could calculate it all, then come to a conclusion on required springs, right?

So, a .10 valve volume (including headspace), with 10cu/in sweep, 1,470 psi. This pressure acting on a 1.375 piston is: 2175 pounds. So, is a spring load for the air pressure needed, or the pressure the air is loading on the piston (2,175 psi)?
"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."


    
This message has been edited by Duane30 on Dec 7, 2017 1:29 PM


 
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Steve in NC
(Login pneuguy)
AR&P

Preload is required. Otherwise energy is wasted compressing the spring...

December 7 2017, 6:13 PM 

...that accomplishes nothing except to violently pop the pump arm open the next time a stroke is begun.

The needed spring force is P x A = 2175# in your example.
Steve

 
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James Perotti
(Login jpsaxnc)
AR&P

Hi Phil, Your getting 12 fpe. with only 51# of closing force,

December 7 2017, 5:34 PM 

There may not be much left to get. Can you post a pic of the valve showing the valve throat and transfer port?

 
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Phil
(Login Duane30)
YF

I'll try...

December 7 2017, 11:31 PM 

SSP Valve <a href="https://imgur.com/gallery/hMl2v" target="_new" rel="nofollow">https://imgur.com/gallery/hMl2v</a>

Valve pin seal is .25" diameter while the pin shank is 5/16" diameter. Brass insert matches the pin profile. When fired, the oring seal does not slide upon transfer port hole, not ruining it by this design.

The valve face is bored .5". This allows for inserts with various port sizes to be inserted creating different valve volumes. The brass insert also has an oring on each side of the transfer port hole preventing losses. On the brass insert face port, it has been machined with an 82 degree taper to better assist flow.
"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."


    
This message has been edited by Duane30 on Dec 7, 2017 11:40 PM


 
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James Perotti
(Login jpsaxnc)
AR&P

Hi Phil, I was able to make 12fpe. in .22 cal. with

December 8 2017, 9:49 AM 

a .120 transfer port. Ideally I would say that the pin blocking the transfer port, should be the same or very close to the dia. of the transfer port. And that the pin should only move back far enough to clear the transfer port, but no further. I think that would get you a little more power. Oh,and no unnessesary beveled edges, they just create head space losses, and the tiny amount of high pressure air, flows just fine without them. HTH.

 
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Phil
(Login Duane30)
YF

Ok on the pin...

December 8 2017, 11:58 AM 

...it is designed to stop once clearing the port. Good there. However, the TP is .21 or so. I'd have to re-measure since now forgetting. That figure seems right.

Will experiment with a smaller TP to see what happens. The gun can make more power (14+ft/lbs) by reducing the valve volume, but really do like the ease of the stroke where it is at.

Now, the portion with the 82 degree bevel, that is on the internal brass portion, not the valve face itself, which is accounted for in the volume; valve face is flat.

For now, it shoots great. Was pondering the Paradigm applied theory as a what if.
"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."

 
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Sloan
(Login s_bryan)
YF

Is the Paradigm ever going to happen?

December 9 2017, 8:10 AM 

I would be very interested. Have been waiting for a long time for a high powered ssp or acp..
And while i am dreaming, offer in bullpup...
And not cost $1800,lol

 
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