.510 cal bullpup development project

[Big Bore Bart]

Lloyd:   Take that steel head down to .588-.598, then undercut that puppy.    Your larger than necessary OD is still choking flow a low lift.  On a metal faced valve the margin only needs to be .005-.010" for a good seal, much more than that will cause sealing problems.

[rsterne]

Sean.... Did you use ball bearings with the driven one having a mass of 5% of the driving one or less, and the spring rate on the driven one being 2000% ?.... just saying....

The collision is kind of like putting a ball bearing up against a bus and then hitting it with a scooter, IMO....

Bob

[Rdsail]

Excellent project and amazing number. I might have to take the 1hour drive to check it out 
I can't image that kind of power our of an airgun.

I'm subscribed.

[lloyd-ss]

Thanks for the comments everyone.  A lot of different thoughts and conjectures going around among us.

BBB, I think I will try and make the head a little smaller but, but not quite yet.

I think the power and efficiency will work itself out ok.  My big concern now is the heavy hammer hit that is needed to open the valve.   It is hard to cock, hard on the trigger assembly, not good for accuracy, and just generally undesirable.   I am going to try and make a pressure balanced valve and see if I can, first, get it to work, and then, cut the hammer force to less than half, and maybe to 25% of what it is now. I can mod the valve body that I already have but I will need to make yet another valve stem and head assy. I know from the past that opening big valves can put tremendous loads on components and break and bend and gall things up, so making a mechanism that is durable, but not excessively heavy is part of the task.

Lloyd

[lloyd-ss]

The first version of the balanced valve is built and installed and working OK.  It has a peek valve head.  The valve throat is now bored out to .578, because of a little clean up while boring the balancing piston hole.  The throat and the balancing piston bore are the same diameter.  The stem is .250.  I forgot to weigh the stem assy before installing it, and it is not a light weight piece. The return spring also acts as a mechanical over-travel stop to keep the balancing piston from coming out of its bore and into the valve throat.  That would be a mess and probably ruin a few things.  Max travel is limited to about .22”. 

The pictures show some of the details.  You can see the valve head and stem with the integral balancing piston and o-ring, and the  1/4” dia rear stem that slides  in the bore of the rear plug. The rear plug, which is static, serves to seal the rear of the balancing cylinder.  It has an o-ring inside the 1/4” bore to seal the rear stem and thus the balancing cylinder. There are three .101 dia bleed holes to feed and exhaust the rear of the balancing cylinder into the high pressure reservoir.



You can also see the long hammer in the pictures.  It had to be that long to accommodate the previous long travel without running completely past the sear and being locked forward, or breaking the sear during rebound.  The hammer is bored out to accept the double spring that was needed to open the previous valve.


Comparison of the previous conventional design .57 throat valve and the new balanced version, at 2600psi.

                                                                                                     conventional valve    balanced valve
Force (from reservoir pressure) holding the valve closed                   663 lbs                      128 lbs
Force (from reservoir pressure) trying to close an open valve            71 lbs                       128 lbs

The first test.
Set up
                                                       conventional valve      balanced valve
Hammer stroke                                       3.1”                          1.13”
Hammer weight                                      193 grams                130 grams
Hamm vel at impact                                  33 fps                     15 fps
Hamm energy at impact                               7.4 fpe                   1.0 fpe
Hamm momentum at impact                   .44 ftlb/sec              .13 ftlb/sec 

Results from the first test 
Hammer energy used                                    7.4 fpe                     1.0 fpe
Energy delivered  at 2600 psi                 approx 650 fpe    approx  240 fpe   

Discussion
The new setup is doing what I wanted, it has greatly reduced the amount of hammer energy needed to open the valve.  The new set up obviously needs some tuning to bring the delivered energy level back up to the 600 fpe range, but the important thing is that the with the balanced valve, a hammer hit at only 13% of the previous hammer energy was able to open the valve and fire the projectile at 37% of the previous delivered energy.  In the conventional set up the gun would not have fired at all.  I think this is  a major step in the right direction.

I am not sure what will be needed to get the delivered energy level back up to the 650 fpe level, but there are plenty of avenues to try.
Lloyd-ss

[rsterne]

Interesting first results, Lloyd.... I will be very curious to see how much hammer energy and momentum is required to get the gun back up to the 650 FPE level again.... It's really too bad you can't measure the lift for the original valve and for each step with the new one....

Bob

[csdilligaf]

Wow Lloyd, from thought to test piece in about a week.  Wish I could get things done that fast.  It looks promising so far.   My balanced valve although on a much lower power has achieved all my goals of lighter hammer, lighter spring and less travel of hammer.  Its going to be interesting to see how well it works for 650fpe.  In the normal set up with a heavy hammer travel 3" is there much of a hang time?  I have never shot bigbore stuff but it seems like it might be a little like shooting a Flint lock?

[rsterne]

Based on Lloyd's supplied data of a hammer veloicty of 33 fps and a travel of 3", that works out to be about 15 milliseconds hammer travel time, significantly less than your reaction time, so I doubt you would notice it very much....

Bob

[PakProtector]

I notice the double nut on the valve spring return keeper. No surprised you decided to go that way, as an experimental I have running a single wee clip for that purpose has spat the clip off and the valve is currently running w/o a return spring... Not that it is doing badly; I am running well below max energy, and that point is a lowly 82 FPE for 43 gr, .224 boolits...

I see hammer force at impact...I suspect you mean 'hammer energy'...as given the clip spitting, I am willing to bet heavily on there being enough force at impact to elastically deform the valve stem axially; the very tip where the hammer hits is no doubt moving at near hammer speed before the head has moved enough to un-seat.
cheers,
Douglas

[lloyd-ss]

Douglas,
Thanks for pointing out that improper terminology.  I just made the correction.  It is important to use the right terminology although I admit I get sloppy/lazy about it sometimes. 
Good thought about the compression in the valve stem during hammer impact.  Just like driving a nail.  So is the E-clip rattling around inside somewhere now?
Lloyd
P.S. I have been distracted by other pressing needs and haven't tried to boost the power back up on the balanced valve yet.  And BTW, I would say that your 82fpe from the .224 is pretty darn decent!

[PakProtector]

Douglas,

Good thought about the compression in the valve stem during hammer impact.  Just like driving a nail.  So is the E-clip rattling around inside somewhere now?
Lloyd

That wee thing is MIA...LOL
cheers,
Douglas

[SeanMP]

Douglas,

Good thought about the compression in the valve stem during hammer impact.  Just like driving a nail.  So is the E-clip rattling around inside somewhere now?
Lloyd

That wee thing is MIA...LOL
cheers,
Douglas

I'll use this moment to jump back on my soapbox.
Here is an example of me breaking my own cardinal rule. Use high grade fasteners. Period. I always specify the best fasteners that can be obtained. In this case I was sent a package of offshore Eclips and I used exactly 2 before throwing them in the bin...those two are on the marauder prototype valves.
I have other identical design valves that have sustained thousands of hits without a failure using simple eclips that are of good and traceable quality.

....of course there is always the possibility that Douglas depressed the keeper as he was installing it.

However....HoloKrome's ad copy states "this is the second most expensive fastener you'll ever buy. The most expensive is the one that fails"
words to live by I guess

Douglas

82 fpe and well below max power...Nice!

[PakProtector]

Hey LLoyd, you have been quiet for quite a spell now...am getting impatient waiting for the next installment of 'as the boolit flies...quickly'
cheers,
Douglas

[lloyd-ss]

Hey LLoyd, you have been quiet for quite a spell now...am getting impatient waiting for the next installment of 'as the boolit flies...quickly'
cheers,
Douglas

Douglas,
Bear with me a little while longer. Almost all of my recent airgun time has been spent on preparing and shipping kits.  I will get back on this shortly.  Part of my hesitation is that I think to really fix this correctly, I  might have to make a totally new valve instead of just being able to mod what I have.  I have to wrap some other things up first.  Thanks for prodding me on, though.  That never hurts (unless the prod is turned on, LOL)
Lloyd