The Daffy Dfly Pist...
 

The Daffy Dfly Piston Design and its Little Rubber Donut  

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Steve in NC
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2018-05-23 21:20:45  

Following up on Jim's thread...

https://airgunwarriors.com/airgun-talk/love-my-plinkster-just-got-my-dragonfly/#post-8610

...here are a few early impressions of my experimentation with my own .177 Dragonfly.

First are the results of swapping out the stock sear for the Plinkster/Stormrider/Varmint/CP-1M/Dragonfly SuperSear.

PlinksterSSkit

1st stage = 8oz

2nd stage = 1lb 8oz

Creep = low to unnoticeable

Short version:  Far superior to the stock trigger.

Next is the potential for AC performance as dictated by such factors as pumping efficiency at high pressure, and hammer bounce elimination.

The latter can be efficiently and effectively achieved with the Plinkster/Stormrider/Varmint/CP-1M/Dragonfly FreeFlightHammer HDD...

PlinkFFdiagram

The former, however, is limited by such factors as pump headspace losses, which, unfortunately, are quite large in the Dfly's pump, due to (my guess) its designer's apparent paranoia about that favorite sport of the MSP shooter:  Overpumping.

As shown in the photo below, the Dfly piston is driven, not by a solid metal rod, but by a squishy rubber donut.  Consequently, pumping force is used, not to directly compress the aircharge, but to first squish the donut.  This has the (theoretically) desirable result of eliminating the possibility of pump damage if pumped to overpressure by a crazed power-mad, over-caffeinated shooter, but has the (very practical) downside of reducing pump efficiency by introducing very large headspace losses as pressure rises and squishing of the donut prevents driving the piston home to properly contact the valve face.

Also, a close look at the circumference of the donut reveals scuffing which suggests that, under pressure, the rubber expands into hard contact with the pump tube, which likely causes wasteful friction and unnecessarily difficult pumping effort.

Clearly, to realize the full potential of this little pumper, we'll need to dump the donut.

DaffyDfly


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Steve in NC
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2018-05-23 23:47:45  

One thing I did get to work was a two-shot repeater mode.

That is to say, after precharging with 9 strokes, you can then take two ~715fps (with CPLs = 9fpe) shots without pumping between shots, then recharge with 8 pumps for another two.  Lather, rinse, repeat.

Potentially useful when hunting or pesting and gets some actual use out of that magazine.

One interesting observation:  The first (high pressure) shot is vewy vewy quiet.  "Springer quiet!"


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DavidEnoch
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2018-05-24 21:56:02  

A+ Steve


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Steve in NC
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2018-05-27 09:18:01  

Thanks David.

Latest news is I've turned the Dfly over to maestro James Perotti.  James kindly offered take a look at its powerplant and realize its potential by making valve and pump what they could and should have been in the first place.

I'm excited to see what James comes up with!


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James Perotti
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2018-05-27 12:16:25  

It's coming along, I'm working on the new piston now, that's the last mod. I just noticed that the barrel is 22" long, that's 3" longer than a Benji barrel. I've got a couple lighter hammer springs for you too.


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James Perotti
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2018-05-27 14:23:32  

Here's the first numbers, with .177, 7.9 grain premiers. 1 pump 313, 2 pumps 467, 3 pumps 563, 4 pumps 634, 5 pumps 688, 6 pumps 736, 7 pumps 774, 8 pumps 811, 9 pumps 844, 10 pumps 863. This is with an increased volume valve, and a lighter hammer spring than stock. I think it would be peppyer with the stock spring, I'll try it later.


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James Perotti
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2018-05-27 15:04:56  

It sounds better with the stock hammer spring, but all the shots were a little slower??  It doesn't look like there is anything to gain over the gun in stock form.  


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Steve in NC
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2018-05-27 15:11:47  

Very Promising!  And I bet the pumping effort - even at 10 pumps - is much easier because the new valve volume is so much larger than stock that the pressure is lower at 10 pumps than it is in the stock valve at only 8.

DflyMV


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robnewyork
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2018-05-27 23:08:46  

interesting build , I know this is a better platform than the 39x for power / experiments.

just read the other thread, I have heard this is not a 12mm muzzle or a 10mm, but rather a .462 rough cut that holds the ldc.


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Steve in NC
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2018-05-28 11:05:00  
Posted by: robnewyork

... I have heard this is not a 12mm muzzle or a 10mm, but rather a .462 rough cut that holds the ldc.

Unfortunately, Rob, the Dfly doesn't have an LDC.  Its sisters - the Plinkster, Stormrider, and Varmint - do (well, sort of), but because the Dfly tube was extended to the full length of the barrel to make room for the pump linkage, that took up the clearance used in the other guns for their LDC. 

So, lacking enough room for even that minimal LDC, the designers (presumably the same fellows who have the rubber donut fetish) substituted a simple plastic muzzle "weight" (?) to support the front sight.


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robnewyork
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2018-05-28 14:04:37  

does the pump arm swing past the plane of the compression tube ?


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Steve in NC
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2018-05-28 14:50:32  
Posted by: robnewyork

does the pump arm swing past the plane of the compression tube ?

Not sure what you mean by "plane of the compression tube," but the arm opens probably less than 120 deg.  An LDC could extend beyond the end of the barrel and tube without fouling the arm.


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JiminPGH
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2018-05-28 16:24:41  

OK, here's what I've done to mine so far.

1. Oiled all pivot points with Secret Sauce.  Reduced pumping effort.

2. Steve's 2 stage trigger.  REMARKABLE improvement.

3. Replaced the rubber piston buffer (?) with a solid nylon spacer.  I'll need to get back on the Combro and do some high pump levels to see if this makes any difference at all.  But at least now I have a non-compressible chain of force from pump handle to valve.

4. Took off the rear sight and added a Williams 5D AG peep.  This isn't the sexy one with the target knobs, but my experience with Williams peeps is once you get it where it belongs, it seldom needs to be adjusted.  Basement accuracy is greatly improved, and I have a pre-existing collection of different apertures to play with.

5. Cleaned the barrel!  HOLY SMOKES!  It took about 15 or more Q-tips pushed thru with a mix of Beeman degreaser and very light trumpet valve oil before I got clean ones coming out.  Once I figured out how easy it is to remove the barrel from this gun, I did the same cleaning routine on my Plinkster, with the same filthy results.  If you have one of these guns, it's incredibly easy to take the barrel off, and they DO need to be cleaned.  FWIW, both my Dragonfly and Plinkster are .177, and Q-tips are the perfect size for these barrels.

6. Added a slit piece of 3/8" ID rubber fuel line to cover the barrel between the breech block and the barrel band.  This makes pumping much more comfortable.  Think Sheridan factory barrel guard pumping grip.

Next step will be Steve's FFHDD.  I'll wait on further results from James' experiments before I decide whether or not to mess with valve volume and/or hammer spring.  Right now, I kinda like it the way it is.


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Steve in NC
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2018-05-28 17:05:11  

Question, Jim: How did you set up the piston length adjustment to accommodate your rigid spacer?

Meanwhile, thanks for the kind feedback on the SuperSear.


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JiminPGH
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2018-05-28 19:22:05  

As your photo shows, there's a roll pin that holds the piston head to the pump rod.  It has a slot that I assume is to allow for compression of the doughnut.  The doughnut is contained by two beveled washers.  I needed the rear washer to support the oil sponge.  I simply sized the nylon spacer to replace the rubber doughnut and one of the beveled washers.  In other words, I made it just long enough so the retaining roll pin could clear the head end of the slot.  That way, as I figure it, the piston head always remains in the same place as zero-pump state, with relation to the valve face.  It can't move further back.  I did not access the piston length adjustment at all.  It still has factory "cam-over" to keep the pump closed.  The only difference I can see is that there is no compressiblity in the pump stroke, and the piston head retains its forward position in the slot due to the rigid spacer, regardless of pump pressure.

Maybe I'm missing something?


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Steve in NC
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2018-05-28 19:49:20  
Posted by: JiminPGH

...Maybe I'm missing something?

If you are missing anything, then me too.  That sounds like a perfectly logical, if slightly aggressive, choice for piston length adjustment. I suspect there's plenty of flexibility in the linkage to take up the lack of donut squish.

I'm looking forward to the tale your Combro tells.


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tkerrigan
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2018-05-28 23:38:27  

Mine is a .22 and I just used steel washers and two diaphragm rubber washers[1/16" each] to replace the donut I'm sure that as previously mentioned it was rubbing the pump tube bore at 8-14 pumps.  I did the usual Crosman stuff to the valve and it's still hard to pump even after that. have since read of two that I didn't know about.  After you shorten the male threads of the valve half, reach in and remove the unused female threads.  Also, drill a hole in the intake check valve from the spring side.    It shoots 14.3 premiers at 800fps at 13 pumps if I remember correctly right now.  I'll get back to it and do some more work on it later on, too many projects in the fire right now.  As hard to pump as it is right now, I think it might need a center section added to the valve.  Regards, Tom


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James Perotti
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2018-05-30 09:25:21  

Hi Tom,  I wouldn't recomend shortnig the threads in the valve. The valves are made from dead soft aluminum, and the threads are a fine thread.


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James Perotti
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2018-05-30 09:34:46  

Hi Jim, I think the valve throat and seal is a choke point in these valves, due to the tappered seat and seal. I increased the porting in Steve's valve, and turned down the valve stem behind the seal. I also increased the valve volume, by turning down the front section of the valve between the o-rings, and drilling two 1/8" holes, to the interior, there should have been a noticeable increase in velocity, but there wasn't.


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Steve in NC
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2018-05-30 09:36:47  
Posted by: James Perotti

Hi Tom,  I wouldn't recomend shortnig the threads in the valve. The valves are made from dead soft aluminum, and the threads are a fine thread.

Probably good advice.  If the valve let go while under pressure while pumping (and Tom says he routinely uses pretty high pump counts and therefore pressures) the results might be messy and even dangerous with the pump linkage being forced open violently.


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Steve in NC
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2018-05-30 09:46:41  
Posted by: James Perotti

...there should have been a noticeable increase in velocity, but there wasn't.

Hi, James.  Have you had a chance to experiment some more with hammer springs?


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tkerrigan
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2018-05-30 10:18:17  

If you increase valve volume, it takes more pumps to increase speed.  Probably just 9 or 10 though, if you want the same pressure as 8 pumps on non-modified.  Regards, Tom


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Steve in NC
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2018-05-30 11:12:05  
Posted by: tkerrigan

If you increase valve volume, it takes more pumps to increase speed.  Probably just 9 or 10 though, if you want the same pressure as 8 pumps on non-modified.  Regards, Tom

Yup.  And James's valve mod's made a big increase - 0.18ci - which is probably pushing a full 2x over the stock (small) volume. 

The biggest single contribution was the turning down of the front section (0.13ci), but he also shortened the checkvalve (0.01), bored out some of the front ID (0.02) and even took advantage of the volume of the clearance between valve OD and tube ID (0.02).

So it should take around 15 or 16 pumps to get to a pressure similar to that provided by 8 in box-stock config'.

If I forgot anything, please correct me, James.


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JiminPGH
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2018-06-01 17:46:21  

Some numbers post rigid spacer installation.  All shot with Benjamin 7.9 gr hollowpoints, AKA CPHP.  3 pumps, 674, 677, 673, 673, 673.  4 pumps, 742, 741, 741, 740, 741.  5 pumps, 786, 789, 788, 785, 785.  6 pumps, 820, 818, 821, 820, 819.  7 pumps, 850, 847, 845, 845, 848.  8 pumps, 865, 866, 868, 869, 867.  These numbers are from a Combro, so your mileage may vary.  In terms of effort vs reward, I'm really pleased in the 4-5 pump range.

DragonflyPiston


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Steve in NC
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2018-06-01 20:05:23  
Posted by: JiminPGH

Some numbers post rigid spacer installation. ...  In terms of effort vs reward, I'm really pleased in the 4-5 pump range.

11.8fpe (nearly 12fpe!) from only 6 pumps.  Not a bad result from merely ditching a donut.

Seriously, Jim:  Nice work!


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ray1377
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2018-06-02 22:49:22  
Posted by: Steve in NC
Posted by: JiminPGH

Some numbers post rigid spacer installation. ...  In terms of effort vs reward, I'm really pleased in the 4-5 pump range.

11.8fpe (nearly 12fpe!) from only 6 pumps.  Not a bad result from merely ditching a donut.

Seriously, Jim:  Nice work!

So Steve

How long is it gonna take you to design a drop in kit to replace that piece of rubber?

That is phenominal results for a .177 pumper. I could live with that 7 pump setting for sure 🙂

Thanks Ray


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Steve in NC
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2018-06-03 00:08:47  
Posted by: ray1377

So Steve

How long is it gonna take you to design a drop in kit to replace that piece of rubber?

That is phenominal results for a .177 pumper. I could live with that 7 pump setting for sure 🙂

Thanks Ray

Well, I'd say Jim is currently the resident authority on that question, but my guess is that McMaster Carr catalog # 94639A678 ($8.67 per pack of 25) would be pretty darn close. 

Hopefully Jim'll set us straight if I've mixed up the measurements.

 


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JiminPGH
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2018-06-03 06:00:37  

The factory doughnut mikes at 1/2" uncompressed.  I started with something I had laying around, and just filed it to fit.  The 1/4" center hole is correct, but there's a small shoulder on the piston head, so I did a slight counter-bore.  The McMaster part would probably be a drop-in with both washers.


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Steve in NC
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2018-06-03 09:32:30  
Posted by: James Perotti

...This is with an increased volume valve, and a lighter hammer spring than stock. ...

Well, James, we (mostly you) did it!  The holy grail of 12fpe on 3 pumps per shot.

Adding an FFH debouncer and tuning for 9 precharge pumps, then 3 charge pumps per shot (= 12 total = 9 conserved air + 3 discharged air) gets (shooting boxed CPLs = 7.9gr)...

 Shot#     FPS          FPE

1 830 12.1
2 831 12.1
3 835 12.2
4 840 12.4
5 844 12.5

Average:

836 12.3

Noise level, as expected, is much quieter than when dumping air -- just as you'd expect with only 3 pump stroke volumes discharged with the shot, instead of 6 or more.  More details to follow.

I think I have a blister  😥 but I'm happy, anyway! 😎 


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nervoustrigger
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2018-06-03 11:44:54  

Great work here, guys!

An ACP is really the way to go.  Dump valves are so terribly inefficient and all that pumping back from zero pressure just robs the fun from shooting.

3 pumps to maintain 12fpe is a very enticing prospect.

If either of you guys have shot enough groups to get a good feel for its accuracy, I’m curious to know how it went.  

 

 

 

 


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