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PostPosted: Mon Dec 29, 2014 2:33 pm 
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Doc Sharptail wrote:
Nice work. I don't have the patience that setting that particular piston for length requires...

Thanks. It did take a few tries to get it right, and it was supposed to be a quick solution. It may actually be easier to just make a threaded adjustable piston :)


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PostPosted: Mon Dec 29, 2014 6:00 pm 
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good stuff Jim that piston reminds me of the one I did a while back. 8)
the o-ring is much better then the piston cup seal.

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PostPosted: Mon Dec 29, 2014 6:21 pm 
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I would advise putting the O-ring much closer to the end of the piston to eliminate the headspace between it and the valve face.... I usually machine the valve within 0.020-0.030" of the O-ring groove and the same on the end of the piston....

Bob

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PostPosted: Mon Dec 29, 2014 8:32 pm 
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rsterne wrote:
I would advise putting the O-ring much closer to the end of the piston to eliminate the headspace between it and the valve face.

Bob


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PostPosted: Mon Dec 29, 2014 10:08 pm 
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That makes sense. I'll add it to the todo list.

Many thanks!


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PostPosted: Mon Dec 29, 2014 11:43 pm 
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With yellow brass the lead edge under 0.012 will deform under pumping pressure and in turn roll onto your oring adding a side pressure. Making pumping harder. It will, then eventually crack. Stay 0.015 or slightly thicker.

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PostPosted: Tue Dec 30, 2014 12:36 am 
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Gippeto: Not a big deal, just an fyi. When a thread gets packed full of pix like this one is it's nice if the pix are cropped and sized like EverHopeful has done. I've seen some where the pix is more than twice as wide as my screen, so I offer them the same program. If they don't know computers well enough to do it, or can't like with a cell phone, then I offer to trim it for them.
And nice work EverHopeful, I wish I had all that toy making equipment. Nothing to be embarrassed about either, the best progress and inventions are made standing atop a pile of failures. I even destroy stuff on purpose just so I know what its limits are. Like your pressure concerns of that hole, which I think is a non-issue, but if in question I'd push a weaker/thinner version to failure just to see. I am curious how much pressure an oem 13xx builds per pump, then how that compares to a flat top mod, but yours will at least give me an idea. I was guessing ~1kpsi at ten pumps on an oem gun, but I'll probably never know for sure. I think making a much longer single stroke is an excellent idea, maybe the best idea. I'm picturing a 15" or so barrel with matching tube and stroke. I suppose getting the bore/stroke specs from that Daisy would be helpful in estimating your bore size you'll want, but with all those tools I'm guessing some trial and error is ok too. I'd imagine once you get it dialed in I'd think you'll have people wanting to buy a kit to convert their guns... A single pump to 500fps (or more) in .22 would be sweet. The only reason people prefer springers over pneumatic is they're one stroke, but I'd rather have a pneumatic if it single stroke and powerful enough. Like the Beeman P17 is my new fav pistol replacing the Webley Tempest. The Tempest is better in most ways and more powerful, but springers are and always will be annoying to shoot.


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PostPosted: Tue Dec 30, 2014 10:40 am 
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Piston testing.... topic65054.html

Bob

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Proud Member of the 2000+fps Club!


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PostPosted: Tue Dec 30, 2014 1:49 pm 
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Ahh! I remember that thread now. Perfect. Once I had my major leak fixed I did a quick test and couldn't get above about 600 psi, so I'm setting to on making an adjustable piston and then I'll look at shaving down those front faces for reduced head-space.

Ace, love that brass front end. I might have to make one of those just so I know that it's in there :)

Chevota, it's tempting to try that big SSP idea just to see how far we could push it, eh? There would be something amusing about a long 1" tube with a big arm. Probably weigh a ton though!


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PostPosted: Wed Dec 31, 2014 12:02 pm 
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Well, it's been a reasonably successful day and a half. I got the adjustable piston done and slimmed down the fronts of both the piston and the valve. Here's the new piston with the previous one above, and the valve on the left:
Attachment:
IMG_8123.JPG
IMG_8123.JPG [ 94.39 KiB | Viewed 241 times ]

I finally got the 1/8-npt joint to the gauge to seal by using a lot more plumbers tape and torquing it more than I was comfortable with. I was sure the glass was going to crack, but everything survived.
Attachment:
IMG_8124.JPG
IMG_8124.JPG [ 132.45 KiB | Viewed 241 times ]

Attachment:
IMG_8126.JPG
IMG_8126.JPG [ 139.17 KiB | Viewed 241 times ]


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PostPosted: Wed Dec 31, 2014 12:20 pm 
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Very nice work.
Are you building a Delrin or Teflon seal for you gauge block?

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PostPosted: Wed Dec 31, 2014 12:22 pm 
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The gauge is just for testing and experimenting, so I'm not worried about it being ugly or impractical :)

Here it is installed on the test gun
Attachment:
IMG_8127.JPG
IMG_8127.JPG [ 149.24 KiB | Viewed 237 times ]


I had to drill the hole in the adapter a lot deeper than necessary to get the tap to cut wide enough threads for the gauge to sit in, so I filled some of the void with a piece of nylon. I've no idea how my total volume now compares to a stock valve, but as far as I can tell from the coarse markings on the little gauge it's doing roughly 100 psi per stroke up to about 9 strokes, which is fairly similar to Bob's results. Mine seems to top out at about 1500 psi though, suggesting I still have too much wasted head space.
Attachment:
IMG_8128.JPG
IMG_8128.JPG [ 118.07 KiB | Viewed 237 times ]


Part of that space is because I left the main bore of the valve front shorter than I could have, leaving wasted space on the inlet side of the check valve. There's room to move the valve face about 1/8" towards the front of the valve, but given the problems I had getting a seal there I think I'll pass on that, at least for now.

I did some very quick testing (nowhere near as thorough as Bob's!) to get a feel for how the system behaves. The PSI readings obviously don't make strict sense - the gauge is only marked in 200 psi intervals, so treat each reading as +/- 100 or more. FPS numbers are only single measurements, not averages as they should be. 10" and 24" refer to barrel lengths.

Code:
#Pumps         PSI     FPS 10"     FPS 24"
1              100      208         218
2              200      304         322
3              400      369         399
4              500      406         472
5              600      449         
6              800      480
7              900
8             1000
9             1000
10            1100
...
20            1500


I think that gives me enough info to feel happy about heading on with the next step - trying to make a relief valve. The gun it's intended for has a 24" barrel, so I need to aim for a pressure of between 500 and 600 psi to hit the magic 499 fps (or there about).

Jim


Last edited by EverHopeful on Wed Dec 31, 2014 12:26 pm, edited 1 time in total.

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PostPosted: Wed Dec 31, 2014 12:24 pm 
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Whitewolf wrote:
Are you building a Delrin or Teflon seal for you gauge block?


It's currently using a delrin seal as I had a convenient offcut to make a washer out of.


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PostPosted: Wed Dec 31, 2014 12:46 pm 
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Have you made any calculations as to your valve space interior?

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PostPosted: Wed Dec 31, 2014 1:09 pm 
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No, I haven't done that. It was intended to be smaller than standard, but obviously the gauge block doesn't help there. It will be interesting to see if I can get to the target fps with perhaps one less pump once the gauge is removed and replaced with the relief valve. I'm hoping I can make that with minimal extra volume.

Any one got any ideas for what shape to make the pressure relief valve? I was thinking of trying a steel needle into a 3/64 inlet bore. Not sure what angle to go with on the tip. I guess 45 is a starting point. I also wondered about a steel ball bearing resting on a delrin washer and a delrin poppet of some shape or other...


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