Breaking down the "Fast Burn Model"

Breaking down the "Fast Burn Model"

Joined: March 1st, 2002, 12:22 am

July 2nd, 2012, 7:55 pm #1


http://www.network54.com/Forum/275684/message/ ... wder+model 

Scot says (post referenced above): "This model is why I'm such a fan of fast, light strikers, valve bodies wide open to the reservoir, and open porting...kick the pellet in the skirt with a high pressure pulse, and get the valve shut as fast as possible..then don't let it open again."

<em>why I'm such a fan of fast, light strikers</em>: This has been demonstrated with the AC39x builds, which I'll attest to first hand (cuz I built one, with copious help )

<em>valve bodies wide open to the reservoir, and open porting</em>: your saying to_not_ restrict air path at all (reasonably speaking), even at the TP? Wider air path for as much of the "conduit" as you can? (Like more lanes on the highway)

<em>get the valve shut as fast as possible</em>..: again, another precept of airconservation. So use a heavy/heavier valve return spring to get it to shut quickly, and allow the delivered air charge to do its thing

<em>then don't let it open again</em>: so either adjust it so the springs stop the bounce, or use a HDD? And the lighter striker wont have the mass/momentum to open the valve again (hdd or heavy return spring)

Ok, so far so good. So open the port on the valve to something simialr to the TP? Some starting point/target wieght for the striker? ANd I'll assume you will need a heavier hammer spring to drive the now lighter strikerfast enough to overcome the now stronger valve spring?

Better order in some more pellets, more 7up and a reflux-friendly snack bowl. Some QT with the chrony is coming up

 


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
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Joined: November 17th, 2006, 3:51 am

July 2nd, 2012, 10:55 pm #2

The light striker model is worth giving a try (maybe more so on the AirForce guns as they have a wider range of spring tensions due to the exceptionally long/wide striker spring).

So far, a light striker is not the way to go for powerbut it is a way to go for gas conservation at lower power,

Has worked its best with constant pressure guns (co2 or HPA). Can find that nearly no-bounce balance and really get the shot count up (but again, not at max speeds).

With PCPs, can get a good shot count, but at a narrower range of pressure. Where a heavy striker night have a sweet spot over a range of 55 or 65BAR, light strikers seem to run right over 40-45bar. Light striker at less energy per shot, but as many or more shots, over a smaller pressure range, does make for good efficiency numbers.
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Joined: April 12th, 2002, 5:26 am

July 3rd, 2012, 3:07 am #3

http://www.network54.com/Forum/275684/message/ ... wder+model 

Scot says (post referenced above): "This model is why I'm such a fan of fast, light strikers, valve bodies wide open to the reservoir, and open porting...kick the pellet in the skirt with a high pressure pulse, and get the valve shut as fast as possible..then don't let it open again."

<em>why I'm such a fan of fast, light strikers</em>: This has been demonstrated with the AC39x builds, which I'll attest to first hand (cuz I built one, with copious help )

<em>valve bodies wide open to the reservoir, and open porting</em>: your saying to_not_ restrict air path at all (reasonably speaking), even at the TP? Wider air path for as much of the "conduit" as you can? (Like more lanes on the highway)

<em>get the valve shut as fast as possible</em>..: again, another precept of airconservation. So use a heavy/heavier valve return spring to get it to shut quickly, and allow the delivered air charge to do its thing

<em>then don't let it open again</em>: so either adjust it so the springs stop the bounce, or use a HDD? And the lighter striker wont have the mass/momentum to open the valve again (hdd or heavy return spring)

Ok, so far so good. So open the port on the valve to something simialr to the TP? Some starting point/target wieght for the striker? ANd I'll assume you will need a heavier hammer spring to drive the now lighter strikerfast enough to overcome the now stronger valve spring?

Better order in some more pellets, more 7up and a reflux-friendly snack bowl. Some QT with the chrony is coming up

 


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
during loading, to something like 25%-30% of the bore diameter?

Wide open upstream;no front face to the valve at all would be ideal in a pcp or co2 gun, some of the Philippine guns manage this stunt. As big a valve volume as you can manage in a pumper(AC tuned)In a full dump, tune for low pressure operation and increase the valve volume to get the best balance of effort and number of pumps.

Not a heavy return spring..set the valve clearance to drag the valve shut fast, use a light return spring to get the gun to self regulate over a wider range. Not applicable to AC pumpers unless you have a pressure telltale or gauge.

HDD absolutely...and the lighter striker does mean it will store less energy on rebound.

Instead of a stronger striker spring, see how much travel you can add..1/4" will add a surprising amount of extra energy at stem impact.

I shoot for a striker weigh 50%-70% of original as a starting point

All the above is just my way of doing things, others have very good success with somewhat different approaches.
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Joined: November 28th, 2002, 6:26 pm

July 3rd, 2012, 5:07 pm #4

http://www.network54.com/Forum/275684/message/ ... wder+model 

Scot says (post referenced above): "This model is why I'm such a fan of fast, light strikers, valve bodies wide open to the reservoir, and open porting...kick the pellet in the skirt with a high pressure pulse, and get the valve shut as fast as possible..then don't let it open again."

<em>why I'm such a fan of fast, light strikers</em>: This has been demonstrated with the AC39x builds, which I'll attest to first hand (cuz I built one, with copious help )

<em>valve bodies wide open to the reservoir, and open porting</em>: your saying to_not_ restrict air path at all (reasonably speaking), even at the TP? Wider air path for as much of the "conduit" as you can? (Like more lanes on the highway)

<em>get the valve shut as fast as possible</em>..: again, another precept of airconservation. So use a heavy/heavier valve return spring to get it to shut quickly, and allow the delivered air charge to do its thing

<em>then don't let it open again</em>: so either adjust it so the springs stop the bounce, or use a HDD? And the lighter striker wont have the mass/momentum to open the valve again (hdd or heavy return spring)

Ok, so far so good. So open the port on the valve to something simialr to the TP? Some starting point/target wieght for the striker? ANd I'll assume you will need a heavier hammer spring to drive the now lighter strikerfast enough to overcome the now stronger valve spring?

Better order in some more pellets, more 7up and a reflux-friendly snack bowl. Some QT with the chrony is coming up

 


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
...(more energetic) strike to release the same amount of gas that a heavier striker would with a lighter strike.

2. A more energetic strike will move the sweet spot pressure toward higher PSIs.

So unless you're willing to live with a smaller gas release (and therefore probably less muzzle energy), you need to expect either a higher fill pressure, or an asymmetric MV-vs-shot_count chrony curve that (for any given efficiency) will probably mean fewer shots per fill.

Steve
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Joined: November 17th, 2006, 3:51 am

July 3rd, 2012, 9:30 pm #5

..getting enough spring to speed a lite striker up to the point where is get back to the same energy as a heavy striker. Even taking some weight from the front end of the striker in order to lengthen stroke a bit hasn't fully made up the energy. Many just have a small area for a striker spring to operate, so when increasing striker tension, end up with a very stiff spring.


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Joined: November 28th, 2002, 6:26 pm

July 3rd, 2012, 10:51 pm #6

...may be even worse in practice.

Steve
Last edited by pneuguy on July 3rd, 2012, 10:51 pm, edited 1 time in total.
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Joined: November 17th, 2006, 3:51 am

July 4th, 2012, 12:48 am #7

Is the striker/valve stem relationship energy....or is it momentum?
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Joined: November 28th, 2002, 6:26 pm

July 4th, 2012, 1:00 am #8

...(i.e., how far the valve head lifts from the seat against the force of pressure), momentum determines how LONG the valve opens (i.e., the length of time it remains open).

Steve
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Joined: November 17th, 2006, 3:51 am

July 4th, 2012, 1:22 am #9

..so evidently, I can't get the lite striker moving fast enough to equal the energy of the heavy striker, at least with a standard sized valve stem.

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Joined: April 12th, 2002, 5:26 am

July 4th, 2012, 2:20 am #10

...(more energetic) strike to release the same amount of gas that a heavier striker would with a lighter strike.

2. A more energetic strike will move the sweet spot pressure toward higher PSIs.

So unless you're willing to live with a smaller gas release (and therefore probably less muzzle energy), you need to expect either a higher fill pressure, or an asymmetric MV-vs-shot_count chrony curve that (for any given efficiency) will probably mean fewer shots per fill.

Steve
from a 50% lighter striker isn't an issue. Most often the power available from a given platform is limited somewhere else, and the extra striker weight is wasting gas through excess dwell.

On the QB based gun that proved out this approach(originating in my AC benjamin work)I was able to drive 14.3g .22 CHP's at 830 fps on co2 at less than 70 degrees Fahrenheit...hardly a low energy tune.That's a 50% lighter striker, factory striker spring, nylon valve head, open face pedestal valve body, and less than .010" added preload on the striker spring. The same setup will give 30 shots between 900 and 930 fps, over a pressure range of 2700-900 psi (Halley small PCP tube) I have no idea what the true volume of that tube is, so the efficiency numbers may be nothing exceptional... but the low noise levels make me think it's pretty good. When I could get my home brew HDDD to work, it got very quiet.

Even the AC Benjies will dump the equivalent of ten pumps in spite of their lightened strikers if I crank the striker spring preload back up to near factory levels..14-18 ft/lbs,depending on whether its a hard steroid type valve or the factory soft face type.

In short, the factory striker is usually overkill...lots lighter doesn't hurt anything.
Last edited by classicalgas on July 4th, 2012, 2:22 am, edited 1 time in total.
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