Start throwing rocks, guys! Just kidding about the rocks.
Give me your initial reaction to the concept.
Why do you think the originals were adjustable? (I'm sorry if I ask questions I know the answer to).
Manufacturing tolerances were "by guess & by golly" on inexpensive air guns. Adjustable pistons were able to correct the head space.
Just my guess???
You don't sound too "sorry"...... lol
Adjustable flat top piston? Sounded like a good idea, at the time.LOL ;D ;D
Got to agree with Bill.
Agree with Bill. Nobody flat-tops the valve to the same length, and nobody has exactly the same lock-up force on the pump arm. A worn pivot hole will add more variability.
These variations can be measured in millimeters, so you need adjustment somewhere to take up the tolerance stack-up.
JMJ
As far as I can tell, the adjustable piston rightfully died with the Crosman 1300 in 1976. It became the 1322 and never had an adjustable piston again. The 760 shed its adjustable piston the previous year in July of 1975.
Since then, there have been no adjustable pistons in the 2100, the 766, the Benjamin 392/397 or C9, etc.
The reason they were adjustable was because the design and available materials of the piston face was such that at some point it would have to be replaced (without replacing the entire metal piston body. To make it replaceable (at that time) it had to be removed, replaced and re-adjusted. So "adjustable" was not a positive feature as much as it was a necessity at the time.
My opinion of the felt oil wiper, the pressed (or pounded on) brass ring end around the center metal shaft, and the not-so-long lasting plastic cup (black, then white, then clear) was and is inferior. Another thing is the high percentage of people that do not set them correctly. I see that.
As soon as design and available materials improved, then the adjustable piston was tossed to the curb like a warm flat six pack of Billy Beer. Only thing was that millions had sold and were / are still out there.
Agreed that DIY flat toppers may not be consistent, but they certainly should be. The first clean pass across the flat means stop. If people are using sand paper or grinders, then shame on them. There's not a ton of meat there (the flat after the cone is gone). Just faced is just faced.
If a pivot hole gets egg shaped, then it should be replaced. I've never had a problem there.
Not here so much, but the populace seems to think flat top equates to more power, yet flat top is only about a tiny bit more pump efficiency... and nothing to do with the power potential of the valve, transfer, hammer / spring etc.
... and that's the way it really is. :)
Since you're giving out answers on the subject...
How does it increase pumping efficiency? ???
Quote from: Underdog on October 14, 2016, 09:21:38 PM
Since you're giving out answers on the subject...
How does it increase pumping efficiency? ???
The flattening (removal) of the face of the valve and then the use of a flat faced piston (no longer having the conical recess) adds that small amount of tube volume to the pump stroke. It's not very much at all as a percentage of the total tube ID x stroke length, but it is an additional tiny gulp of volume for the piston to force into the valve each pump. Maybe saves one pump out of 15? 20? Not really significant.
We get very similar results with flat top and not flat top setups where both valves are ported on the exhaust end and a small increase in pressure chamber volume allows both to equally allow for more pumps netting higher fps (and fpe). 115 additional fps at 20 pumps is a good expected increase for both .177 and .22 calibers. It's there if you need it, but otherwise for plinking, targets, etc. just treat the gun as stock.
Both the stock Crosman rubber cup for stock gun's pistons... and a well seated o-ring at the end of a flat top piston can do a better job of compressing that volume of air than the old plastic setup from the 60's and 70's. Cheaper and easier to replace, too if one gets nicked or abused from lack of lubrication.
If nothing else, I am trying to open a discussion that will possibly prove helpful in the end. Please correct me if I am wrong in my observations.
Forgive me if I state what is obvious to the rest of you. I'm starting to get a handle on what the mods are, and what they do...
So if I understand this correctly, piston/valve mods that remove the conical sections from each, only incrementally increase the pump volume so you get to a certain pressure just a bit faster.
The valve modifications that increase valve volume will give you more air to dump when the valve is opened, provided you pump enough times to get there. (I assume cutting off a section of the threaded cap increases volume. What other mods will increase valve volume?)
Valve modifications that open up the air flow route (valve stem, valve exhaust, transfer port, barrel port, and bolt/probe) allow that volume of air to dump faster, hopefully increasing FPS.
Now is where I get a bit fuzzy on what's done to the hammer and spring... What's the purpose of these mods?
I think I get the longer barrel idea. If you have a short barrel, the pellet only gets up to a certain speed before it gets out the end, and the rest of the volume of air gets dumped...
Am I understanding all this correctly?
(Oh and trigger mods are usually just to smooth out the raspy trigger, yes?)
Everything you said indicates that you understand correctly.
The stronger hammer spring provides additional kinetic energy for the hammer to strike the valve and keep it open slightly longer for release of a larger dump before the internal spring forces it closed again. Actually, you can do the same thing by putting a lighter spring in the valve. Easier to just get a stronger spring (or power adjuster if you're a tweaker speed demon).
i think they went by the wayside due to cost --- look at their airguns of yesteryear and today ---THEN more real metal and real wood vs NOW plastic and pot metal ..... as well as trying to mass market and keep things at a price point for the average joe (sorry joe)
So what other mods can be done to the valve to increase the volume?
Also at what point do you stop doing mods because of a stock length barrel? Or asked another way, how many mods would you do if you stuck with a stock length barrel?
Quote from: Underdog on October 15, 2016, 12:53:43 AM
So what other mods can be done to the valve to increase the volume?
Also at what point do you stop doing mods because of a stock length barrel? Or asked another way, how many mods would you do if you stuck with a stock length barrel?
What gun model? What caliber?
I've always had difficulty adjusting the flat top piston. If there were a non- adjustable piston that was already the correct length, that would be very helpful. :-*
Quote from: 7624452 on October 15, 2016, 01:26:12 AM
I've always had difficulty adjusting the flat top piston. If there were a non- adjustable piston that was already the correct length, that would be very helpful. :-*
(http://i437.photobucket.com/albums/qq93/JUSTJOHNY/001.jpg)
the correct length would be subjectable --- the saving grace would be the cup as it is compressible --- those are close but not the same in the above picture
Quote from: Davio on October 15, 2016, 01:08:52 AM
What gun model? What caliber?
A 1322 rear cocker. I got mine going to stock specs now, but would like just a little more umph out of it. Don't think that the 6.5 fpe is quite enough.
Quote from: eric on October 15, 2016, 12:45:00 AM
i think they went by the wayside due to cost --- look at their airguns of yesteryear and today ---THEN more real metal and real wood vs NOW plastic and pot metal ..... as well as trying to mass market and keep things at a price point for the average joe (sorry joe)
Agreed. :)
Flat top reduces head space in the pump, increasing effective compression ratio and potential to make pressure. That they're typically of stouter construction than the plastic fodder adds to that potential.
Swept volume is determined by stroke length and bore size...which are determined by the tube id and the linkages...swept volume remains un changed by flat topping. Most of the efficiency gains with a flat top come from reducing the head space. Getting the faced off portion as close to the sealing o-ring as practical pays dividends....parts do become more susceptible to damage from dropping as the pressure side of the o-ring groove gets thinner. Personally use .030".
Weaker valve spring will lower cracking pressure of the check valve, allowing slightly more of the compressed volume to actually enter the valve.
Opening force is very much a product of valve sealing area and has comparatively little to do with the force provided by any reasonable valve spring.
For example....
.290" sealing diameter equates to 66 lbs force to crack the valve for each 1000psi.
Nice little videos by Sean Pero; Adjustment is covered in part two.
[youtube]https://www.youtube.com/watch?v=5_y-OS5JZAQ]https://www.youtube.com/watch?v=5_y-OS5JZAQ[/url]
[youtube]https://www.youtube.com/watch?v=oMduvk5PVQU]https://www.youtube.com/watch?v=oMduvk5PVQU[/url]
Al
Well done, Al - a total "sticky" thread if you ask me :-*
I will totally refer to this later when working on my pumpers. Thanks again and have a great weekend :-*
So here's Davio (Alchemy) non-adjustable setup...
(http://i61.photobucket.com/albums/h54/o-townFLA/crosman%201322/141BC78D-DC10-4D8C-94E9-D73D817F0DF7.jpg) (http://s61.photobucket.com/user/o-townFLA/media/crosman%201322/141BC78D-DC10-4D8C-94E9-D73D817F0DF7.jpg.html)
And some chrony numbers from to stock to FTP
STOCK
Created: 10/09/16 10:40 PM
Description: STOCK 10 pumps CPHP
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 14.30
Temp: 68 °F
BP: 30.05 inHg
Altitude: 0.00
# FPS FT-LBS PF
10 404 5.18 5.78
9 401 5.11 5.73
8 406 5.23 5.81
7 406 5.23 5.81
6 405 5.21 5.79
5 414 5.44 5.92
4 409 5.31 5.85
3 408 5.29 5.83
2 411 5.36 5.88
1 409 5.31 5.85
Average: 407.3 FPS
SD: 3.7 FPS
Min: 401 FPS
Max: 414 FPS
Spread: 13 FPS
True MV: 407 FPS
ALCHEMY
Created: 10/16/16 12:45 PM
Description: FTP 10pump
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 14.30
Temp: 69 °F
BP: 29.98 inHg
Altitude: 0.00
# FPS FT-LBS PF
10 465 6.87 6.65
9 470 7.02 6.72
8 471 7.05 6.74
7 480 7.32 6.86
6 473 7.11 6.76
5 474 7.14 6.78
4 469 6.99 6.71
3 473 7.11 6.76
2 472 7.08 6.75
1 471 7.05 6.74
Average: 471.8 FPS
SD: 3.9 FPS
Min: 465 FPS
Max: 480 FPS
Spread: 15 FPS
True MV: 472 FPS
Great review. Looks like it works. :-*
Granted I added my own little sauce to the mix with a lighter valve spring, trimmed some fat off the valve stem and added Davio's "boss buddy"....
Here's a 3 pump to 16 pump chrony string... Purged the valve completely at 16 pumps. Just ran out of time to find that max....
Created: 10/16/16 12:24 PM
Description: FTP 3-16
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 14.30
Temp: 68 °F
BP: 29.99 inHg
Altitude: 0.00
# FPS FT-LBS PF
14 544 9.40 7.78
13 525 8.75 7.51
12 522 8.65 7.46
11 500 7.94 7.15
10 490 7.63 7.01
9 473 7.11 6.76
8 458 6.66 6.55
7 448 6.37 6.41
6 430 5.87 6.15
5 410 5.34 5.86
4 387 4.76 5.53
3 344 3.76 4.92
2 325 3.35 4.65
1 285 2.58 4.08
Average: 438.6 FPS
SD: 79.7 FPS
Min: 285 FPS
Max: 544 FPS
Spread: 259 FPS
True MV: 439 FPS
Curious to see the max on that thing now.
Quote from: o-townFLA on October 18, 2016, 08:53:13 PM
Here's a 3 pump to 16 pump chrony string... Purged the valve completely at 16 pumps. Just ran out of time to find that max....
Created: 10/16/16 12:24 PM
Description: FTP 3-16
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 14.30
Temp: 68 °F
BP: 29.99 inHg
Altitude: 0.00
# FPS FT-LBS PF
14 544 9.40 7.78
13 525 8.75 7.51
12 522 8.65 7.46
11 500 7.94 7.15
10 490 7.63 7.01
9 473 7.11 6.76
8 458 6.66 6.55
7 448 6.37 6.41
6 430 5.87 6.15
5 410 5.34 5.86
4 387 4.76 5.53
3 344 3.76 4.92
2 325 3.35 4.65
1 285 2.58 4.08
Average: 438.6 FPS
SD: 79.7 FPS
Min: 285 FPS
Max: 544 FPS
Spread: 259 FPS
True MV: 439 FPS
At your fifteen pump mark you're at 525 FPSwhich is almost 50 FPS faster than my stock 1322 with the same size pellet. Your FPE is also about 1.5 FP higher. Your fifteen pumps still gets better results than even my 20 pumps. At 20 pumpsI get an average of 491.6 FPS, and average of FPE of 7.676. Your FPS is still about 30+ higher, and FPE is 1 FP higher. I'd say it was worth it... I dunno would I get the same results from the flat top and modified valve, but it's certain worth a shot at some point.
Created: 10/01/16 11:43 AM
Description: 1322- 15 pump Cros Destroyer .22
Distance to Chrono(FT): 0.25
Ballistic Coefficient: 1.000
Bullet Weight(gr): 14.30
# FPS FT-LBS PF
5 478 7.26 6.84
4 475 7.17 6.79
3 472 7.08 6.75
2 479 7.29 6.85
1 482 7.38 6.89
Average: 477.2 FPS
SD: 3.8 FPS
Min: 472 FPS
Max: 482 FPS
Spread: 10 FPS
True MV: 477 FPS
---------------------------------------------------------------------
Created: 10/01/16 11:37 AM
Description: 1322- 20 pump Cros Destroyer .22
Distance to Chrono(FT): 0.25
Ballistic Coefficient: 1.000
Bullet Weight(gr): 14.30
# FPS FT-LBS PF
5 498 7.88 7.12
4 494 7.75 7.06
3 487 7.53 6.96
2 489 7.59 6.99
1 490 7.63 7.01
Average: 491.6 FPS
SD: 4.4 FPS
Min: 487 FPS
Max: 498 FPS
Spread: 11 FPS
True MV: 492 FPS
Those are great numbers :-*
Good job Dave!
@UNDERDOG
I'd say go for it! As mentioned, I did add a few extras as shaved plunger, lighter valve spring, even polished the bolt and lubed it w/ moly paste.
I ported, angle grinded the transfer port on the valve, stuffed the stock piston myself but cut to many threads off, resulting in a catastrophic failure. One reason why I bought the Alchemy Airwerks piston/flattop setup...
Here my chrony #'s with the self mod
Created: 10/11/16 11:01 PM
Description: mod 10 3-15
Notes 1: Catastrophic Failure On 16th Pump
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 14.30
Temp: 62 °F
BP: 30.06 inHg
Altitude: 0.00
# FPS FT-LBS 18.24mm
13 530 8.92 7.58
12 523 8.69 7.48
11 507 8.16 7.25
10 496 7.81 7.09
9 481 7.35 6.88
8 464 6.84 6.64
7 452 6.49 6.46
6 429 5.84 6.13
5 409 5.31 5.85
4 381 4.61 5.45
3 354 3.98 5.06
2 317 3.19 4.53
1 283 2.54 4.05
Average: 432.8 FPS
SD: 79.6 FPS
Min: 283 FPS
Max: 530 FPS
Spread: 247 FPS
True MV: 433 FPS
(http://i61.photobucket.com/albums/h54/o-townFLA/crosman%201322/A3CAC857-E974-41AE-8649-340B20E2ADCA.jpg) (http://s61.photobucket.com/user/o-townFLA/media/crosman%201322/A3CAC857-E974-41AE-8649-340B20E2ADCA.jpg.html)
(http://i61.photobucket.com/albums/h54/o-townFLA/crosman%201322/690563DE-03A9-4F71-A6EE-92BA6B63B674.jpg) (http://s61.photobucket.com/user/o-townFLA/media/crosman%201322/690563DE-03A9-4F71-A6EE-92BA6B63B674.jpg.html)
It is always good to see (and learn from) independent chrony numbers. I'm glad you guys are getting the type of results that I get. :)
Quote from: Davio on October 21, 2016, 09:00:41 PM
It is always good to see (and learn from) independent chrony numbers. I'm glad you guys are getting the type of results that I get. :)
Thanks brother for the stellar work and quick shipment! Now to justify the purchase of your breech... Lol
Could you PM me a price for your breech and explain the benefits of either a steel or aluminum breech