GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on November 01, 2014, 10:52:47 PM
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A while back I had a discussion about which was better, an adjustable metal Flat-Topped Piston and Valve or an adjustable metal piston carrying the original Crosman pump cup, meeting with a shortened (but still cone shaped) valve front end.... It is fairly well known that the tapered front on the Crosman 13XX/2289 valve is slightly too long, and hits the bottom inside center of the pump cup before the edge of the cup can hit the shoulder on the front of the valve, resulting in greater headspace than necessary.... Therefore, the first step was to machine 0.030" off the front of the cone on the valve so that the rubber pump cup touches the end of the cone at the same time the end of it touches the valve flange near the O-ring.... Once done, the pump cup conforms very closely to the front of the valve.... The idea of the adjustable metal piston is to put some pressure on the pump cup, squeezing it tight against the valve front to create minimum headspace.... This minimum headspace is already achieved, of course, with a flat-topped piston and valve because you have two flat surfaces touching....
I made an adjustable piston with two heads, one flat-top, and one carrying a Crosman pump cup.... I also had a stock plastic Crosman piston for comparison purposes.... In order to measure the pressure inside the valve, I drilled out the back half of a valve and threaded it 1/8"-27NPT for a 3000 psi gauge with 100 psi increments.... I machined up a Delrin spacer for inside the valve to provide a spring seat (in the original location) with a tiny (3/64") hole through it for the pressure to the gauge, and adjusted the dimensions until the internal volume of the valve was the same as a stock 13XX/2289 valve.... I shortened a 1377 pump tube just behind the stake that locates the valve (thanks to Skanzy for donating one to the cause and sending it to me) so that the gauge cleared the back, and added an 8-32 setscrew on the side to prevent the back half of the valve from turning when I mounted and removed the gauge.... The front trigger screw (actually a 1/4" long high tensile 8-32) was used to secure the valve in addition to the rear stake.... Here is a photo of the parts....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/TestValveandPistons_zpsf98378a9.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/TestValveandPistons_zpsf98378a9.jpg.html)
and here is the assembly.... I used a stock 2289 pump arm and linkage, and a 3/16" solid steel pivot pin (easily removable)....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/PumperTest_zps94dddaaf.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/PumperTest_zps94dddaaf.jpg.html)
I started with the stock piston and recorded the pressure at each pump to 20 pumps, then at 22, 25, and every 5 pumps up to 50 pumps.... I then removed the stock piston, adjusted the length of the one with the Crosman cup to put it under slight compression (you can feel the resistance when the handle is 1" from closing) and repeated the test.... I then removed the valve, replaced the valve front end with the flat one, installed the flat-topped piston (adjusted so that resistance on the handle is felt at 3/4" from closing) and tested one more time.... I actually ran each test 3 times and used the average, although the pressures were quite close on each run, basically within my ability to read the gauge (about 20 psi).... I then graphed the results, as shown below.... EDIT: Testing done at 2500' altitude, so subtract about 9% from the number of pumps at sea level for any data presented in the graph....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/2289Pistons_zps436278b6.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/2289Pistons_zps436278b6.jpg.html)
Obviously, either of the adjustable metal pistons is a HUGE improvement over the stock one.... Using stock springs, a 13XX/2289 starts to retain air at about 1500 psi, which you can't reach with a stock piston.... The flat-topped design performed the best, although at 10 pumps and below there is very little difference.... in fact there is only about 1 pump difference at 12-13 pumps.... Above that, however, the more you pump the greater the margin for the flat-topped piston, which is what I expected to see.... As the pressure rises, even with the adjustable metal piston, the Crosman rubber pump cup starts to compress from the air pressure, and the headspace gradually gets greater and greater, lowering the compression ratio of the pump, and requiring more pumps to reach the same pressure.... It tops out at about 2400 psi at 50 pumps, which is 50% more pumps than the F-T-P takes to reach that pressure (~32 pumps).... I stopped at 40 pumps with the F-T-P (2520 psi), although the pressure was still building slowly....
I didn't test a "stuffed" piston, where metal rods are glued into the slots in the side of a Crosman plastic piston to stiffen it.... This mod is often accompanied by fitting an O-ring between the cup and piston, and a washer under the cup, to reduce the headspace, in conjunction with shaving the cone on the end of the valve.... Obviously this can't be any better than the adjustable aluminum piston using the Crosman cup which I tested.... It is just a cheap way to gain some benefit, how much is gained being in proportion to the care used.... It would be better than stock, for sure, and it wouldn't take much improvement to reach 1500 psi where you have to worry about retaining air....
I am very pleased with the results of these tests.... Not only do they clearly show the improvements that can be made, but they also give a plot of valve pressures inside a stock valve, which is a piece of information I haven't seen in this much detail before.... I hope you all find this information helpful....
Bob
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Whoa! That's what I call research. I have a stuffed piston 1322. Thanks for this.
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Excellent info there. I am a little surprised the flat top and the metal piston with cup are so close in spec.
Have you done or are you planning on doing anything with oversized piston and compression tube configs?
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I'm not surprised they are close at below 1000 psi (<5%), and I'm also not surprised that they are quite different above 2000 psi (16-50%).... Rubber compresses, just that simple....
Nope, I did that when I built my Disco Carbine Pumper and Millennium Pumper, using the 7/8" OD tube and Benji 39X pump linkage with a home made F-T-P.... All the data on that exists....
Bob
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I'll dig around for that thanks.
How was the heat buildup? Surprised the cup can take 50 pumps.
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I was only pumping in sets of 5 with reading the pressure in between, so you could feel some heat in the tube but not a lot.... Also, my hand was on the top of the tube, acting like a big heat sink.... *LOL*.... The cup looked perfect....
http://www.gatewaytoairguns.org/GTA/index.php?topic=37401. (http://www.gatewaytoairguns.org/GTA/index.php?topic=37401.)
http://www.gatewaytoairguns.org/GTA/index.php?topic=39328. (http://www.gatewaytoairguns.org/GTA/index.php?topic=39328.)
Bob
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Wow Bob!!!!
Thanks for doing this test & making the graph. This really helps me to understand what the mods are actually doing. This is one of your posts that I can really relate to.
One question.....how would the pressure build on a reduced valve volume like on the 2100? I believe it is around .072 cu.in as compared to the .1122 cu.in.of the stock 1300 valve.
Thanks
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Thanks. Had the Millenium tagged but not the .25 Disco thread.
What I am really liking about that graph is it looks like a pretty consistent 100 psi per stroke up to number 10 for the ft and alu with cup. Not to bad a deviation from there up to 20 as well. That is incredibly useful data and really shows up the advantage over the stock setup.
Now if someone will just make a "Stroke Dot" reticle:)
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I didn't test other valve volumes, but if you leave the pump swept volume the same, the number of pumps to reach a given pressure should be in the ratio of the volumes.... In other words, if you use a valve that is half the size, it should take half as many pumps.... double the size, double the pumps....
I think your volumes on both valve are slightly too large.... did you subtract the volumes occupied by the spring and the head of the poppet and the check valve?.... Your ratios of volumes are pretty close, though, I have a note in my old files that a 2100 valve is 60% of the volume of a 2289 valve.... your numbers give 64%.... Basically it should take 6 pumps instead of 10 (or 12-13 instead of 20) to hit the same pressures, assuming you have the same headspace....
Likewise, if you use a 2100 pump on a 2289 valve it should take you about 70% the number of strokes that it takes with a 2289 pump.... ie 7 instead of 10, 14 instead of 20....
There is a bit of a curve in the first 10 pumps.... It's about 600 psi at 5 pumps, and about 1100 at 10 pumps, for the F-T-P.... 1900 at 20 pumps....
Bob
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Great information you have put together here, Bob. I know a good bit of time went into this so thank you for sharing!
Your data clearly shows the benefits of the FTP and FTV combo and in reducing headspace to a minimum. I know some will go to great lengths to stretch the limits of energy the 13xx platform will produce and I respect that.
I just want to share my perspective with others as to why I prefer shimming the pump cup and stuffing the piston. Doing that netted 11fpe on 15 pumps on a long-barreled .177 cal pumper for almost zero cost using miscellaneous parts in the shop...a washer, O-ring, and some 1/8" steel rod. Also, while the pump cup being rubber and having some give to it limits the ultimate pressure, it has a benefit in terms of reliability. The flat top setup puts a lot of stress on the pump linkage and pivot pin, many people reporting and posting pictures of their worn-out pistols and carbines after relatively low numbers of shots.
And as a practical matter owing to the enjoyment of shooting a pump gun more than five times a day, I lose interest fast if it takes more than 15 pump strokes. Well, even that feels burdensome compared to the reward:effort ratio of a springer or even a hand-pumped PCP. Of course I realize I don't [/i]have[/i] to pump 30 times just because I have a FTP/FTV but still, that's a lot of pumping to do even occasionally and proportionately each successive pump yields less FPE per stroke, reaching a point of diminishing returns.
So each approach has its advantages and disadvantages but what constitutes "best" has a lot to do with the individual's criteria for best. That's how I like to look at it.
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You are absolutely correct that much of the benefit of an F-T-P can be had for little to no cost, particularly at low pump numbers.... I disagree, however that a PROPERLY ADJUSTED F-T-P is responsible for wearing out the linkage and pivots.... If you set the piston into too hard a contact with the valve that can happen, but not it is is adjusted to just touch, just enough to hold the linkage closed after the gun is fired.... After that, by the time you have 1000 psi of air in the gun virtually all of the load is from the air pressure, NOT the piston contact, and the load is the same at the same pressure, regardless of whether you use an F-T-P or a rubber cup.... It's just easier (not as critical) not to screw up with the cup.... It is the increased pressure, not the F-T-P, that wears things out (including your arm!)....
In terms of minimizing pumping even at low pump numbers, there is NO reason (other than cost) not to use an F-T-P.... even at 3 pumps, they are better.... virtually an unmmeasureable difference, but better.... No question there is diminishing returns on continuing pumping, but for those who want high power, the F-T-P offers the way to reach high pressures with the fewest pumps.... On the other hand, a stuffed piston with and O-ring and washer, pinning the pump cup, and file off the end of the valve, will give you 90% of the benefit, up to 10 pumps, at virtually no cost....
Bob
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I agree about the _properly_ adjusted FTP. At least logically that makes sense. Apparently it's not easy to get right though, just judging by the anecdotal evidence. Don't you need some amount of deliberate interference in order to create a cam-over effect to help keep the pump arm closed?
It may indeed be mostly because of the increased pressure but I would be surprised to learn that most users of FTP/FTV-equipped guns tend to use over 15 pumps for most of their shooting. A 500ct tin of pellets at 20 pumps each is 10,000 pump strokes. They'd be easy to spot though. It's the airgunners with forearms like Popeye. ;)
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It's actually easy to get the piston length correct.... You want the pump arm to feel resistance when it is 1/2"-3/4" from closing, with the gun fired.... Less than 1/2" the pump arm will fall open after firing.... More than 3/4" and you are unduly stressing the linkage and pivot pin.... The biggest problem is people using high pressures without replacing the roll-pin with a smooth steel pivot pin.... The roughness of the roll-pin really takes a toll on the pump arm hole at higher pressures....
I was one of those (Popeye), during the development and testing of my Uber Pumpers and Uber Carbine.... *LOL*.... Now most of the shooting I do with my .177 Uber-Pumper is 3 pumps of the 2200 tube, giving >500 fps.... Occasionally I'll use 10 pumps when I want 800.... I sold the .22 cal version, as although I got over 900 fps the 1400 pump wore me out past 10 pumps, where I could get 750 fps (18 FPE).... The only pumper I use much is my .22 cal Uber-Carbine, using a 2200 pump tube, which is tuned for two shots at 600 from 20 pumps....
Bob
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Thanks for the reply Bob.
That confirms that I'm on the right track. I mostly shoot my 2100 with 3 pumps for around 540fps & my 760 with a reduced volume valve about the same fps with 5 pumps.
As for my valve numbers, that is what I got by filling with water he backhside of the valve with the poppet then the front side with the check valve then adding the 2. I think I left the spring out.
Thanks!!
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I saw this was a "Bob thread" and knew it would be worth reading. Excellent tests and very valuable info, especially the pressure gauge. Thanks for taking the time to run the tests, this should be a sticky.
I have never dug in that deep with mine, but I have a flat top I received 2 years ago waiting to go in. Maybe this winter.
Great post Jason as well.
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plinker, the two valves overlap where they thread together, it would be hard to get that exactly right....
Bob
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Hi Bob at times I feel I should say Sensi...
What was the intake passage volume? On the modern 13xx I have seen them vary from .06 to .085 and I use brass 1/16 brass tubing to sleeve it down to .03
most of the passages have been right at .55 long pre matching to the cup and .5-.51 after...
at
.08" x .5" you have headspace that is equal to about losing ~1 pump in 40 pumps which is about 45-60 psi in 20 pumps using .1 for valve volume.
.06"x .5" = losing ~ 1 pump in 70 or about 20-35 psi in 20 pumps
.03 x .5 = losing ~ 1 in 283 or 5 psi
Have more I wonder about but the Seahawks are playing....
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And is it possible to get you to give the actual figures I can read the graph to get a general idea but I am very interested in a very close way of figuring just how the pump efficiency curve goes at psi/pump...
also freshly oiled versus not... oops commercial over...
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The intake passages in both valves were 0.060", I couldn't get a 1/16" drill into them.... I realize there is a tiny gain to be made there on BOTH valves, slightly more on the full length (after shortening) than on the flat top.... but we are talking 140 psi difference at 20 pumps (1760 vs. 1900) between the cup and the flat-top (both adjustable metal), which is over 2 pumps.... In fact the F-T-P did 10 psi more at 18 pumps than the cupped did at 20 pumps.... The valve holes are 0.200" difference in length between the two front ends x 0.060" D = 0.000565 cu.in = 0.0093 cc.... If you cut the hole in half to 0.030", the new volume would be 1/4 that, so the gain would be 0.75 x 0.093 cc = 0.0070 cc.... Using your valve volume of 0.1 CI = 1.64 cc (which I agree with) that represents an improvement in the compression ratio of 0.43% for the cupped piston relative to the F-T-P if both were sleeved.... We don't really care about how much we are losing now, only how much of that loss could be reduced in one setup compared to the other.... Using your 20-35 psi estimate for the total loss of a 0.060" hole 0.5" long, the relative gain we are talking about if both are sleeved down to 0.030" would be 6-10 psi....
I think that I have shown that the differences between the cupped piston and the F-T-P is insignificant below 10 pumps, which you would expect, as they both eliminate most of the headspace in the stock design.... However, as the pressures increase, the cup compresses from the load on it, and the headspace increases, reducing the pumping efficiency relative to the F-T-P.... At 2400 psi, I found that difference to exceed 50% (50 pumps for the cupped piston vs. 32 for the F-T-P....
Bob
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WOW! The first Rsterne post that I understood after only reading it once. And the first I completely understood at all. Thanks for lowering to my understanding level Bob. Those are some money saving results. Time to pull the 1377 carbines apart.
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Bob, you make Boyle proud!
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Thanks for the response
I have not disagreed about the conclusions I was asking because I am trying to develop an understanding of the pump efficiency of each system...
examples:
@
10 pumps with a pump cup system 100% eff( ignoring intake passage) for a .1 valve getting air from a 3.5" X .62" stroke is 1510 psi,
70% is 1057 and 60% 906, it looks on the graph to be about 1050
15 pumps with a pump cup system 100% eff( ignoring intake passage) for a .1 valve getting air from a 3.5" X .62" stroke is 2265.4 psi,
70% is 1585.7 and 60% is 1359.2, it looks on the graph to be about 1480 psi?
So I am interested in your actual figures for both just so I can build as accurate of a model (spreadsheet) of each as possible...
I have been setting mine by shimming till just contact and then shimming .04 further which leaves about .5" before handle closing.
this of course pre compresses the cup that amount... It does leave me wondering if I should shim less or more and wondering the # of pumps before headspace is created for say .03, .04 .05 of shim.
Since I have stuck with the stock barrel bands I feel that sticking around 1500 psi and once in a great while 1700? keeps me from egging out the linkage and pump tube...
And sticking to budget builds lets me build more...
The MK/13xx is looking like I can build some valve volume with about the same swept volume as a 2100...
and that has been my design philosophy just to see what can be done on a budget which means higher volume with the limits of the lower psi of a pump cup...
there are the issues I wonder about like at what psi do you need to beef up the linkage/tube and go to a better barrel band...
with a flat top piston closing at .5"-.75" that means that after cam over where does that .04 or so of piston travel go, if everything is built to take it has to be flexing the pump tube which is attached to the barrel band/barrel?
So I know I am not building the best it can be I am trying to balance/budget/durability/power/accuracy...
but this is the best oppratunity to get a very realistic efficiency plot...( if you feel like sharing the specifics)
and then I will have a more realistic(smarter guess ;) ) of what the bored out about .23 c.i. mk valve and .75" x3.5" pump is likely to get...
or .75 x 4.2 or .75 x 5... etc.
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I agree that the efficiency drops off as the number of pumps increases.... This is from a number of reasons, I'm sure, some of which are compression of any rubber components (cup and O-rings), heat, flexing of the linkage, etc.etc.... I've tried doing mathematical models, and they never work because you are chasing a moving target.... There are numerous sources of error in my experiment, including my ability to read the gauge.... I recorded the psi to the nearest 20 psi (1/5th of the 100 psi divisions on the gauge) which is typical practice when reading a scale.... I then averaged the three readings and used the resulting average to plot the graph.... There were a few points that didn't "fit" (obvious single point bumps in the graph), so I adjusted those numbers to smooth the curve, but I never adjusted two adjacent numbers.... I feel that the graph represents the data I collected better than any single set I recorded....
I have worked through the geometry of the pump linkage with a drafting program, and my calculations show that when the end of the pump handle (7.75" from the pivot) is 0.5" from closing the piston is only 0.004" from maximum travel.... The pivot point in the linkage is (2 / 7.75) x 0.5 = 0.129" from its "home" position, and the 2.625" long link lever, when it drops that last 0.129" only travels 0.004" at the piston end.... I have no problem with the preload in the system over that 0.004"....
I get a slightly different theoretical pressure curve, using the formula I got from Steve in NC.... With zero headspace I get the following, using your 0.62" bore and 3.5" stroke (1.056 CI) and 0.1 CI valve.... followed by the pressure I got with the F-T-P and the efficiency....
5 pumps - 791 psi - 620 psi - 78%
10 pumps - 1567 psi - 1120 psi - 71%
15 pumps - 2343 psi - 1550 psi - 66%
20 pumps - 3119 psi - 1900 psi - 61%
Introducing a 2% headspace (2% of the valve volume = 0.002 CI) gives the following pressures from Steve's formula....
5 pumps - 745 psi - 620 psi - 83%
10 pumps - 1406 psi - 1120 psi - 80%
15 pumps - 2005 psi - 1550 psi - 77%
20 pumps - 2548 psi - 1900 psi - 75%
30 pumps - 3485 psi - 2360 psi - 68%
40 pumps - 4253 psi - 2520 psi - 59%
As you can see, trying to compare reality with theory is pretty tough.... Steve's formula predicts a pressure rise of 365 psi from 35 pumps to 40 pumps, and in fact the pressure with the F-T-P only went up 60 psi, indicating the pumping efficiency at that point is only about 16%.... Think about it this way.... using the differences in predicted and actual pressure rise:
0-5 pumps - 83%
5-10 pumps - 500 / 661 = 76%
10-15 pumps - 430 / 599 = 72%
15-20 pumps - 350 / 543 = 64%
20-30 pumps - 460 / 937 = 49%
30-40 pumps - 160 / 768 = 21%
Then compare that with the increase in velocity and energy you get in each pumping increment.... any you will soon realize the futility of pumping past a certain point.... It's fun to do to get the numbers.... but gets old really fast....
Bob
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oops I left out I used 14.3 for atmospheric pressure because of the altitude my back yard is at...
I have tried to design for between 15 and 22 pumps on mine because I felt that the cup system really starts struggling past that and my builds have seemed to follow that rule.
that is close to what I see on the graph...
I really appreciate you taking the time to post your findings and to discuss how to interpret them...
I have a great fondness for these darn pumpers even though the are very inefficient in comparison to acp/pcp designs...
AND it is comforting to know that a 20-25 fpe pump and dump is doable and that 30-40+ fpe is achievable with a ACP design... especially if you flat top...
Did you find any probs with the gages reliability due to the very sudden pressure changes...
Once again thanks for your post they have helped me enjoy my tinkering much more than I would have if figuring it all out by myself...
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The above was using 14.7 psi per atmosphere.... I just looked up my air pressure at 2500' and it's only 13.4 psi, so my pump was significantly more efficient than the above numbers indicate.... ::)
With 2% headspace, and using 13.4 psi per atmosphere....
5 pumps - 679 - 620 - 91%
10 - 1282 - 1120 - 87%
15 - 1828 - 1550 - 85%
20 - 2322 - 1900 - 82%
30 - 3177 - 2360 - 74%
40 - 3877 - 2520 - 65%
Wow, that's a pretty big difference when you use the proper atmospheric pressure.... :o
Bob
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I have worked through the geometry of the pump linkage with a drafting program, and my calculations show that when the end of the pump handle (7.75" from the pivot) is 0.5" from closing the piston is only 0.004" from maximum travel.... The pivot point in the linkage is (2 / 7.75) x 0.5 = 0.129" from its "home" position, and the 2.625" long link lever, when it drops that last 0.129" only travels 0.004" at the piston end.... I have no problem with the preload in the system over that 0.004"....
"
on that I did not do the math my gut was figuring at least twice that at .01 or so, now I also have a more realistic view of what is happening in that part of the system. ;D
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Thank you for the information, Bob. If you still have that rig setup, would you mind doing a test with a properly stuffed and shimmed piston? That is with all eight piston cavities stuffed with 3/16th inch steel rod (precisely matched for each 4) pressure fit (and then secured) and a 4 mill thick washer under the pump cup, and a 5 mill thick O-Ring between the outer cup and piston and the valve nose correctly shaped.
Just by penetration testing it seems that the correctly stuffed and shimmed piston produces results that are pretty close to the Aluminum Cup Piston. And if it is as close as it seems, it can save a lot of people a lot of money, especially if they only want to go up to 20 pumps.
All of my modded 13xx guns are designed for under 20 pumps, thus I use either stuffed pistons, or adjustable aluminum cup pistons.
I also not that you only examined the form of cup pistons that use the stock cup, and not those that are more metal with a lining of ruber just to form a good seal.
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I see no point, it can never be as good as the adjustable aluminum piston.... As discussed earlier in the thread, it will end up between the stock piston and the aluminum cup piston, depending on how good a job you do.... If you do a good job, up to 10 pumps, your results will be so close to an F-T-P that it won't matter, and vastly superior to a stock piston, IMO....
Bob
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I see no point, it can never be as good as the adjustable aluminum piston.... As discussed earlier in the thread, it will end up between the stock piston and the aluminum cup piston, depending on how good a job you do.... If you do a good job, up to 10 pumps, your results will be so close to an F-T-P that it won't matter, and vastly superior to a stock piston, IMO....
Bob
Ok I thank you for the data that you have provided.
I do always attempt to make my stuffed pistons as close to 100% perfect as my skills and tools allow me to (all rods the longest that will work for a pressure fit and measured with a micrometer to 0 measurable difference for each set of 4, and the washer fit as perfectly as possible, the O-Ring carefully chosen, and the valve nose carefully shaved with the measuring aid of a Cup Seal that has been bisected).
I do thank you again for this great data.
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This topic is almost 2 years old, but it is very relevant to my current 1322C build. I was very surprised at the pressure possible with a FTP setup. I don't know if I will use 40 pumps but I have used 20 pumps (at 5835 foot elevation) so I am no where near 2500 psi at this time. But I am going to add additional valve retention for possible future needs. Thanks for an excellent presentation of this and other projects, Bob. ;)
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CraigH's bump on this brought it to my attention as well. Cool write up Bob! Just curious, how did you dump the valve after each pump set?
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IIRC I cracked the gauge loose....
Bob
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Bob's posts never fail to impress, I always learn something lol. Thanks, Bob!
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WOW
I was going to get a disc pcp gun.
But after reading this thread i decided not to.
The pump and or scuba tank and hook up to tank valve ect= Big $ on top of the price of the gun.
But a 1377 with mods is a lot less $ and less to pack around if you go hunting or to the range.
Plus no co2 to buy.
and you can get the same valve pressure as a disco. AND PUMPING BUILDS MUSCLES!!!
i can pump and save some $ and get some exercise at the same time. it a no bran-er. Pumping for DOLLARS
Don
P.S. I went to walmart and pickup a 1377 $49.84 +tax.
I already have a new 24" .177 Barrel to put on it.
so i will order a stock and a front sight for the 24" barrel and play with it for a while before i do more upgrades.
Don
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Don, watch your step, sounds like you're falling into the rabbit hole!
I say that, and I'm about to get another valve and a 22 barrel for 1377 that i've already spent too much on.
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I need to reread this thread when I can see straight so I am subscribing
Mike
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Hi GumpIsrael
I understand what your saying.
lets see a picture of this million dollar 1377. lol
I did install the 24" barrel i had already in .177
I hit the farm supply store got a new trigger spring $.87.
I Polish the trigger sear and molly grease on all pivot points.
Took some of the curve out of the washer that's behind the trigger to remove some drag . trigger is good enough for me now.
i will do light mod to the valve and transfer port to help the air flow.
I don't think i will do flat top piston.
but i will get the rear stock and metal breech so i can install my scope.
after i get that done I will crony it and tune the barrel length and that all i am going to do.
looking to get 700 + fps or close it .177 with 7.9gn pellets.
with the price of the 1377 pistol and new barrel, breech. and stock plus a some small parts. I sill have less than $150 in it.
That's $70 less than the disco alone.
and if i did the flat top piston that will bring the total up to around $180 still less than a disco.
something like this. http://www.gatewaytoairguns.org/GTA/index.php?topic=38154.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=38154.0)
Don
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I found this PDF last night. Called ; Crosman 13xx HotRod Tech.
Here is the link: http://www.readbag.com/mp661k-sitedocs-13xx-hotrod (http://www.readbag.com/mp661k-sitedocs-13xx-hotrod)
it is a case study of the valve modding.
I did the poppet valve tapering mod and lighter spring and stretched the hammer spring 1/4" so far and 24" .177 disco barrel.
at 25 pumps it shoots through a 3/4" pine board 7.9 gn pellet, my gamo Silent cat with a IGT gas piston will not do that.
with the info here and this link. I believe that i can turn my 1377 pistol in to a board split-er with 10 pumps. or less.
accordion to the chart here after all mods done 10 pumps will equal to 25 + pumps. it dumps all air at 25 pumps.
the lighter spring in the valve makes it pump a lot easy-er.
I like my Crosman 1377 more and more each day.
Don
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Bob I wonder if you're FTP pressures could have gone higher sooner with the use of a milspec 90 duro o-ring like the one Tim sells? I have noticed that even compared to 90 duro Buna, the o-ring from Tim can build much higher pressure at say 15 to 20 pumps. Of course when I say that I'm talking about feel based on pumping resistance as it builds. No gauge to show me actual pressure like you setup. I'm assuming you used 70 duro in your tests.
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It's possible that a harder O-ring will compress less, reducing the headspace.... That would allow the pressure to build slightly faster, particularly at high pressures.... and at the limit would allow a higher peak pressure to be reached.... Whether a different material would seal better and therefore improve pumping efficiency could be a matter of the individual gun, finish on the pump tube, and several other factors.... ie I have no idea.... ;D
I don't remember if I used a 70D or 90D in the tests.... It could have even been a Crosman original, and some of those are 80D....
Bob
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I want to revive this old thread so I can ask a couple of questions.
1. Does it take a muscle builder to pump a flat top to 15 pumps?
2. What kind of speed can you get from a 7.9 grain pellet and 15 pumps on the flat top
If this was already mentioned I apologize for not seeing it.
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Nope, not that hard to pump to 15, even 20 pumps.... I hit about 785 fps with a 24" barrel at 15 pumps with 7.8 gr.... The barrel length will make a big difference.... You do not really need to work on the ports in .177 at those pump numbers, or change the springs, as long as the gun doesn't retain air.... If it does, I would fit a softer valve spring, such as the one found in the trigger group, before using a stronger hammer spring....
Bob
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I saw a flat top piston and valve for $75 and a flat top piston and valve with a spring for $95. I guess the spring is to make sure that the valve dumps all the air. I think that these were crosman piston and valve and they had no spacing adjustment. They are either a great fit or not with no adjustment.
Is this system the one that was tested?
I don't think that I would want to go over 15 pumps so do you think that I would need the system with the extra spring?
I have a 14" barrel now so what kind of speed could I expect. This is a crosman barrel and if it doesn't prove to be accurate I will probably try a 24" barrel.
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Around 14-15 pumps is just about where a 13XX/2289 with stock springs and an F-T-P starts retaining air.... As I said, a slightly softer valve spring is the best solution if that happens.... although you can use a stronger hammer spring, it just makes the gun harder to cock.... With a 14" barrel, you would likely be around 700 fps.... I would be very nervous of a F-T-P and valve without adjustment.... It only takes a few thou to either have way too much headspace (limiting pressure) or binding the linkage and wearing it out very fast....
Bob
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I was thinking that no adjustment would have to be set up so that you were not getting the full benefit or you would be risking damaging the system.
Where can I find an adjustable model?
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I got Alchemy Air Werks' special valve (see http://www.alchemyairwerks.com/store/p78/The_High_Performance_PUMP_RP_VALVE.html (http://www.alchemyairwerks.com/store/p78/The_High_Performance_PUMP_RP_VALVE.html)), but not the same one he (David Grimes) supplies to go with the FTP. I originally was going for the latter; but he talked me into this other one, even though he doesn't make as much money from it as he would selling the other valve and FTP pair. He believes this other one is actually better (if you don't mind pumping). See the blog post explanation at http://www.alchemyairwerks.com/alchemy-blog/post-9-the-pump-rp-valve-questions-answered (http://www.alchemyairwerks.com/alchemy-blog/post-9-the-pump-rp-valve-questions-answered) .
I do wonder about the difference in compression ratio which comes from getting rid of the head space which would be important to getting a high maximum power in high altitude. So far I'm nearly at sea level, but I do hope to move to 4000-5000 feet elevation in a couple of years. That's not like 10,000 feet, but you do lose something like 15% of the atmospheric pressure you had at sea level. A benefit of this valve is the greater air volume held; so although it takes more pumps to bring it up to pressure, more power is attained by virtue of the fact that the high pressure is maintained longer as the pellet gets farther down the barrel, something that might be extra beneficial with the longer barrels. (I have 18". I might have gone for 24", but I was concerned that it would be impractical after I got the LDC on it. Now I'm thinking 24" would have been fine.) Bob, can you compare this setup against what has been discussed in the preceding pages? Thanks.
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I bought mine from crosmods and am very happy with it. I did the stuffed piston using some steel rods. That made a big difference, however I decide to go with the adjustable flat top and it works great, better than the stuffed piston. Mine has the 14" barrel in .22 and I get, actually, what do I get in regards to fps? Seem to have misplaced my info.
I found it. With 14.3 CHP, @ 10 pumps it is around, 512 fps, 15 pumps 561 fps, 17//18 pumps gets me 570 fps around 10fpe. Anything over that requires a heavier spring to get all the energy to dump. I find that going above 15 pumps has really little gain for the amount of potential wear and tear increases.
Have fun, my brother got a hold of mine and he is loving it. He has gained quite the fan club where he lives, everybody wants to buy it.
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Doug, as I showed in the first post in this thread, an FTP dramatically reduces the number of pumps to get to a given pressure, but by eliminating headspace and flex in the pump cup, it also allows you to reach a higher pressure, if that is your goal....
Adding additional volume inside the valve definitely can increase the maximum power, but will of course increase the number of pumps proportionally to get to a given pressure.... Generally speaking at low pump numbers, you will get slightly more velocity with a smaller valve.... while at high pump numbers you will get more velocity with a larger valve.... At the limit, big valves and high pressure produce the most power....
Bob
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Out of interest, do you think there would be a measurable difference in pressure attaintable between a metal head and a delrin head made to the same specifications?
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There is a small amount of springing (compression) in a Delrin head, or give in the fork portion from the force on the pin, if that is made from Delrin.... so yes, at high pressures there may be a small difference.... In addition, with enthusiastic pumping I have melted/scorched a Delrin piston head.... I now make the entire piston from metal.... and fit the O-rings as close as possible to the end of the piston and valve to minimize the headspace....
Bob
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I apologize if it has been covered elsewhere. I am just getting started and trying to read all of the quality information I can get my hands on. When you are grooving your metal pistons, do your groves have round or square shoulders in the bottom of the grove?
If you don't mind sharing, what process do you use for grooving?
Thanks! This post and subsequent thread has been an excellent read.
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For pump piston and pumper valve O-rings, I use a radiused groove to minimize the groove volume.... Under pressure, the O-ring gets forced into the outer, front corner of the groove in the piston, and the outer, rear corner of the groove in the valve.... It you use square-bottomed grooves (which is normal for O-rings) you will have extra volume in the inner corners, which will fill with HPA, increasing the headspace and lowering the compression ratio.... I also keep the grooves as close as practical to the end of the valve and piston, for the same reason, to minimize the headspace.... You really only need about 0.030", you can even go less than that, but don't ever drop the valve or piston, you will dent the groove when it hits the floor (don't ask how I know that)….
Having the smallest possible headspace is more important at high pressures, it doesn't make a huge difference to the pressure inside the valve at low pump numbers.... I don't have any photos of me cutting an O-ring groove, but I just grind a tool from a piece of HSS lathe tooling to the shape and dimensions of the groove I want, and then turn the groove on my lathe.... I keep the width quite close to the O-ring cross section (eg. ~0.110" for a 0.102" O-ring) and cut it deep enough to have about 10% compression on the O-ring when installed.... For a 0.102" CS O-ring I would cut the groove so that the diameter at the bottom of the groove is about 0.180" smaller than the ID of the pump tube.... and then use a 90 Durometer O-ring to keep compression to a minimum....
Bob
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That is exactly what I needed to know. Thank you.
If you have the time or inclination, please feel free to chime in over here with anything you think I need to know (or at least what I should know to start) - https://www.gatewaytoairguns.org/GTA/index.php?topic=154848.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=154848.0)
I am currently reading everything I can get my hands on. Trying to catch up in a hurry.
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I use a radiused groove to minimize the groove volume....
That would never have occurred to me, your dedication to efficiency is truly admirable! If I could chip in with another machining question, how are you making the grooves for a circlip as done here (https://www.gatewaytoairguns.org/GTA/index.php?topic=9588.msg1551107#msg1551107)?
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Form tools are incredibly useful items to have Jack. If you have a grinder and a piece of HSS, most any shape is possible, just look at the job that needs doing and grind the cutting edge and relief that you need.
A thread cutting tool is an example of a form tool, as is a grooving tool...internal or external. Trepanning tools, radius cutters etc...all form tools.
This fellow shows a simple technique that results in some accurate tools sized perfectly for your Sherline...
https://www.youtube.com/watch?v=k2a9ywCEK_A (https://www.youtube.com/watch?v=k2a9ywCEK_A)
Al
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Form tools are incredibly useful items to have Jack. If you have a grinder and a piece of HSS, most any shape is possible, just look at the job that needs doing and grind the cutting edge and relief that you need.
A thread cutting tool is an example of a form tool, as is a grooving tool...internal or external. Trepanning tools, radius cutters etc...all form tools.
This fellow shows a simple technique that results in some accurate tools sized perfectly for your Sherline...
https://www.youtube.com/watch?v=k2a9ywCEK_A (https://www.youtube.com/watch?v=k2a9ywCEK_A)
Al
That there is a great video. Thanks Al
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Form tools are incredibly useful items to have Jack. If you have a grinder and a piece of HSS, most any shape is possible, just look at the job that needs doing and grind the cutting edge and relief that you need.
Definitely one of the areas in machining where I haven't ventured much into yet.
This fellow shows a simple technique that results in some accurate tools sized perfectly for your Sherline...
Fantastic watch, thanks for sharing! And guess who has a lot of broken drill bits to play with ::)
I would just be wary of using a Dremel so close to the lathe because of the dust, I know he covers it but it still made me wince.
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No need to wince Jack. ;) Cover things up and clean them well afterwards. Tool post grinders (factory or ad-hoc) are nothing new, and were once fairly common...and a handy bit of kit too.
Al
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Wow-
"That there is a great video"
All I can say is that just taught me more than I knew about making tools
THANK YOU !!!
Now if I could just get enough courage to start using my OLD lathe
{Old like, a rise n fall tool holder and foot powered. I guess before 1875, but what do I know }
Then maybe, just maybe I could build some of the stuff stuck in my head
But, that could be.,.,., who knows?? I might live thru it.
Again Thank you
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. I then removed the stock piston, adjusted the length of the one with the Crosman cup to put it under slight compression (you can feel the resistance when the handle is 1" from closing) and repeated the test.... I then removed the valve, replaced the valve front end with the flat one, installed the flat-topped piston (adjusted so that resistance on the handle is felt at 3/4" from closing) and tested one more time
[(http://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/2289Pistons_zps436278b6.jpg)
sorry, I've read the whole thread and this part isn't clear to me, are you saying the blue line is for STOCK valve + Al piston?
if correct, where can you get this adjustable/pump cup piston?(in EU)
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Look at the photo in the first post.... The stock valve has a cone on the front (top right).... The aluminum piston is on the bottom left and fits onto the front half of the adjustable piston at center left (instead of the flat top piston with O-ring).... I don't know of anybody who makes them commercially....
Bob
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and is the blue line you graphed for stock valve + mod piston or were both modded??
it really is not clear to me, prolly I'm missing something
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Yes, the blue line labeled "aluminum piston with cup" is with the stock valve...meaning the end of the valve is the original conical shape that matches the rubber cup.
Only the red line labeled "aluminum flat top piston" has both parts modded...meaning they each have flat faces so they meet with minimal headspace.
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Yes, the blue line labeled "aluminum piston with cup" is with the stock valve...meaning the end of the valve is the original conical shape that matches the rubber cup.
Only the red line labeled "aluminum flat top piston" has both parts modded...meaning they each have flat faces so they meet with minimal headspace.
"dang" so the valve mod unless it has more volume is pointless(at low pumps)
and i guess that piston figure would be even better with the poly tube mod you described in your pdf?
so much mods info here, is there a more basic-technical thread list for beginners on modding crosman pistols?
Thanks nervous trigger
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The volume of the valve is unchanged in Bob’s comparison so we can see how much pressure is achieved with X number of pumps depending on the type of piston and head geometry. If any of the configurations had a different valve volume, we could not directly compare them in this way.
Incidentally, in most cases you would not want to increase the valve’s volume. Perhaps you might for a 13xx that has been retrofitted with a long .22 barrel but it would be counterproductive for a short barrel in either caliber. It would just take more pumping strokes to build the same pressure yet it would yield no benefit…just louder because the valve would be belching air well after the pellet has left the barrel. Some folks have actually gone the other direction and inserted something in the valve to reduce its volume so it takes fewer strokes to build pressure.
From my perspective, the big takeaway from Bob’s excellent study is that there is a massive benefit to using a stiffer piston and placing a shim of some kind behind the pump cup to take up any headspace (make it so the cup squeezes against the valve when you close the pump arm). At anything up to 10-12 pumps, there’s no need for a flat-top piston or valve. For example, we can see an almost 50% increase in pressure over the OEM arrangement at 10 pumps. The reason that is appealing to me is because that’s about as much pumping effort as I’m willing to invest. I mean, sure it might be fun to pump 40 times and see the max power I can get. I’d do that once…okay, twice so I can see if it’s repeatable. But that’s about it. From then on, it’s never going to see more than a dozen pumps.
Regarding your question about the poly tube transfer port, I think it had been established as a slight benefit for .22 cal and a slight detriment to .177.
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The volume of the valve is unchanged in Bob’s comparison so we can see how much pressure is achieved with X number of pumps depending on the type of piston and head geometry. If any of the configurations had a different valve volume, we could not directly compare them in this way.
Incidentally, in most cases you would not want to increase the valve’s volume. Perhaps you might for a 13xx that has been retrofitted with a long .22 barrel but it would be counterproductive for a short barrel in either caliber. It would just take more pumping strokes to build the same pressure yet it would yield no benefit…just louder because the valve would be belching air well after the pellet has left the barrel. Some folks have actually gone the other direction and inserted something in the valve to reduce its volume so it takes fewer strokes to build pressure.
From my perspective, the big takeaway from Bob’s excellent study is that there is a massive benefit to using a stiffer piston and placing a shim of some kind behind the pump cup to take up any headspace (make it so the cup squeezes against the valve when you close the pump arm). At anything up to 10-12 pumps, there’s no need for a flat-top piston or valve. For example, we can see an almost 50% increase in pressure over the OEM arrangement at 10 pumps. The reason that is appealing to me is because that’s about as much pumping effort as I’m willing to invest. I mean, sure it might be fun to pump 40 times and see the max power I can get. I’d do that once…okay, twice so I can see if it’s repeatable. But that’s about it. From then on, it’s never going to see more than a dozen pumps.
Regarding your question about the poly tube transfer port, I think it had been established as a slight benefit for .22 cal and a slight detriment to .177.
agreed, less pumps the better
if there was no loss I'd go for bigger valve/TP
in a case like this tho: https://www.gatewaytoairguns.org/GTA/index.php?topic=45838.msg156257639#msg156257639 (https://www.gatewaytoairguns.org/GTA/index.php?topic=45838.msg156257639#msg156257639)
would shimming be enough or do you need to file the valve's tip?
just curious, the gun shoots perfectly out of the box(unlike a 2100 i had to return)