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Old 11-03-2011, 05:23 PM   #911 (permalink)
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Mine doesn't need as long a travel length for the ports to become fully exposed, the tapering of the valve nut allows for a shorter travel.

I've also had better luck with the rubber seal than the Teflon.
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Old 11-03-2011, 05:33 PM   #912 (permalink)
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Fan of EMR
I'll 3rd that. The rubber one seems to seal better.
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Old 11-03-2011, 08:29 PM   #913 (permalink)
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Originally Posted by y0da900 View Post
Mine doesn't need as long a travel length for the ports to become fully exposed
how can you tell?
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THE-SHOOTIST Anyone chubbin' like me for this?
mailmanmike Since Monday! That's more than 4 hours though, so according to those cialis ads I should see my doctor.
tlane77 I think for a non-chemical chubby it's 6 hours before its time to see a doctor. So you should be good for another couple hours.
splattttttt I wasn't goin to google "chubbin" because I assumed it had to do with fat. The lard type, not the fun stuff. But what ever feelings Jeff's experiencing, then they must be of the fun like stuff...
tlane77 He's got a woody for your woods.
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Old 11-03-2011, 08:51 PM   #914 (permalink)
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Unless the powertube people use is a huge deviation from normal and has the ports significantly further away from the cupseal end than usual, then the valves that I did should open fully with a shorter throw. Because the valve nut face is tapered, and the point of contact between the cupseal and the valve nut is away from the center, the ports are inherently pulled into the valve body away from the valve nut.

There is a diagram I made earlier in the thread showing this, I'll try and dig it up.
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Old 11-03-2011, 09:01 PM   #915 (permalink)
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I know that when holding the entire assembly in hand, it's easy to tell by compressing the tube, and that will expose the ports. Most often they DON'T clear 100%, but I find that a negligible factor because air will find its way out. But I know that's not good enough for you
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THE-SHOOTIST Anyone chubbin' like me for this?
mailmanmike Since Monday! That's more than 4 hours though, so according to those cialis ads I should see my doctor.
tlane77 I think for a non-chemical chubby it's 6 hours before its time to see a doctor. So you should be good for another couple hours.
splattttttt I wasn't goin to google "chubbin" because I assumed it had to do with fat. The lard type, not the fun stuff. But what ever feelings Jeff's experiencing, then they must be of the fun like stuff...
tlane77 He's got a woody for your woods.
splattttttt land
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Old 11-03-2011, 09:45 PM   #916 (permalink)
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Not opening 100% is fine - a lot of traditional Nelson valves only expose around half of the port area when fully open.
Nelson Valve Evolution (Project Leprechaun)
Nelson Valve Evolution (Project Leprechaun)

Just tossed this together - thought I had done it earlier but that was a comparison to spherical and conical valve nut faces.

Both my valve design and a stock Nelson valve at rest. Notice the ports are partly recessed into the valve nut on a traditional valve and partly out on mine.




Both valves open 3/32". Traditional is a little better than half exposed, the ports in mine are completely out.


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Old 11-03-2011, 10:28 PM   #917 (permalink)
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I can see how with the ports angled to your design, the pt only needs a short amount of dweel time to do its job. Looks great.
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THE-SHOOTIST Anyone chubbin' like me for this?
mailmanmike Since Monday! That's more than 4 hours though, so according to those cialis ads I should see my doctor.
tlane77 I think for a non-chemical chubby it's 6 hours before its time to see a doctor. So you should be good for another couple hours.
splattttttt I wasn't goin to google "chubbin" because I assumed it had to do with fat. The lard type, not the fun stuff. But what ever feelings Jeff's experiencing, then they must be of the fun like stuff...
tlane77 He's got a woody for your woods.
splattttttt land
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Old 11-03-2011, 10:29 PM   #918 (permalink)
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Just ran a 12 gram through the gun. Same setup as yesterday to start with, then I came back to it and added the fluted hammer since I wanted to be under 300 to start.

14" Kaner, blow-match paint.
open face bolt
Lapco fluted hammer
y0da valve
Lapco #6 PT
horizontal dropout changer valve
Testing at room temperature.

316 - shimmed valve spring, heavy hammer.
-- - no reading
275 - added fluted hammer
282
300
297
301
300
290
276
291
306
287
301 - jammed on this shot - the oring I was shimming the valve spring washer with blew out.
254 - valve spring reseating itself here?
265
259
275
281
287
261
264
282
288
288
281
277
284
275
268
281
289
296
291
288
250
241
217

So, 39 shots over 250. Average FPS, 285. Standard deviation of 15.

Not bad, but I'd still like to detune it to ~275 fps with a reg, and get some better paint for consistency. I think it was a bit oblong despite using the same ball for the whole test. Shot curve stayed pretty good and flat until the last two shots. In fact, despite the occasional fluctuations, FPS stayed very strong right up until the last two shots, by which point I could hear slight valve pop when cocking.

Again, I have concerns about the tolerance between the power tube and valve collar. Evidently there was enough gas to blow the oring I was using to shim the washer with in half, and out into the hammer, which made the gun jam. This is with the original anti-blowby oring in place. Like I mentioned before, there is enough room to physically wiggle the Lapco PT in there, and I'm not sure the o-ring is enough to stop blowby.

I'm also starting to think there's no good reason to shim the valve to manually reduce throw, as it doesn't seem to affect chrono numbers. In fact, once the shim blew out, velocity dropped and then returned where it was, presumably after the valve spring re-seated.
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Last edited by russc; 11-03-2011 at 10:52 PM.
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Old 11-03-2011, 10:33 PM   #919 (permalink)
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Want me to send you a really nice ball? Made by Nelson paint.
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THE-SHOOTIST Anyone chubbin' like me for this?
mailmanmike Since Monday! That's more than 4 hours though, so according to those cialis ads I should see my doctor.
tlane77 I think for a non-chemical chubby it's 6 hours before its time to see a doctor. So you should be good for another couple hours.
splattttttt I wasn't goin to google "chubbin" because I assumed it had to do with fat. The lard type, not the fun stuff. But what ever feelings Jeff's experiencing, then they must be of the fun like stuff...
tlane77 He's got a woody for your woods.
splattttttt land
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Old 11-03-2011, 10:45 PM   #920 (permalink)
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no worries, I'm sure I can find something passable around here.
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