Let me train (torture you with) my horrible english a little and speak like paintgun valve expert... (bassically most from us are all already experts):
The main advantage of the nelson valve train is his excessive simplicity or better maximalized primitivism.
In powertube, the valve stem is here integrated with the valve port to the barrel. Bolt, powertube and hammer are here in one arrangement, it is simple and compact. There are few parts and commonly only two seals what have key importance for function. Most parts are easy to manufacture by machining and the final montage is easy. KISS principe is that what is there working.
The main "internal balistic" advantage of nelson valve train is that you have here direct path from the valve chamber to barrel chamber - what allows you get with the nelson valve train good CO2 efficiency easy. That is really good... but the problem is that it is perhaps the only one "internal balistic" advantage.
The problem is that with the parts simplicity and integration you are here limited in many other ways. The powertube sealing (powertube x bolt, powertube x valve nut) is problematic and comonly you have leaks with every shoot here. Hammer is cocked here opposite to the valve, what means that you are restricted in spring combinations. Max. airflow boost / powertube ID entlargement has here limitations because the hammer and the whole trigger mechanism is on the powertube.
You can make the details of nelson marker better, from better materials, with better finish than were on common older nelson. You can find the optimal hammer weight, spring combination for this great, simple design. But possibilities of excessive tunning are here limited.
Make comparsion with sheridan (not for valve train bashing, but only for comparsion of the natural advantages and disadvantages of the designs):
In sheridan valve train the manufacturing and the montage process is more complicated. There are comonly more key seals, more parts, or parts what are harder to manufacture. It is hard to have here slick, good, direct airflow from valve chamber to barrel. But because there is no parts integration in function or in space, you can easily work on every part and maximalize thier effectivity.
Good performance tunning is not easy thing. With Nelson you have easier work and it is easier to get really good
results. Thier simplicity and direct air path allows nelsons commonly be more efficient than common sheridans. But I think that beyond some extend, with the nelson valve train you are more limited than with sheridan.
From this point of view, the whole "nelson evolution" concept has here imho turned in bad way.
Imho modern high quality nelsons (Carters, Phantoms, new Grey Ghosts, Gargoyles, and even old high princed tournament grade markers) have already reached thier natural limitations.
There are still some details which can be perfected (imho it is shape of the seal on powertube, optimal expansion and flow in the valve chamber)... and the common markers are commonly not perfect in the basic things like optimal spring combinations, optimal hammer weight, optimal sealing, optimal barrel. With that you can do something.
But work on the main remaining disadvantages of the nelson valve train is imho really hard and it ruins the KISS principe extenssively. I see the biggest space for improvement in powertube sealing. Theoretically when you have common 0,1mm clearance/space (0,004") on diameter here, between powertube and valve nut and the same space between powertube and bolt, then when you have powertube with ID 5,2mm (0.2"), the crosssection of the powertube ID is 21,23mm2 and the crossection of the unsealed space can be (2x) ~0,95mm2. That is 21,23 X 1,9 - what is 8,9%. With smaller powertube with ID 4mm (0,157") will it be 14,33mm2 X (2x) 0,9 - what is 14,3%. With larger clearances on the unsealed places the effect will be even worse. That means that you loosing around 10% of gas with every shoot by leaks.
But dry put here seal and you will see where is the common nelson design simplicity... The parts and things will be alot complicated.
That what you doing here is basically not tunning - you working basicaly on new construction. That is not bad, but it is simply different. Being some years design engineer in industry, I dare to say that when you working on new construction, it is very important to be not limited with the old construction, be able let the all old things go to hell and work only with that what is simply more practical.
But you drying here to work with natural disadvantages of nelsons, which can be not solved without full design reconstruction... but you will preserve the basic nelson pump-construction. With this attitude you can get perhaps some good results, but in fist place you will imho ruin the main natural nelson advantages. In reality, the evolution of Nelson has been already finished before some years. The in-line concept has been evolved with Automags etc.
You can do what you will, but you will here everytime struckt in two problems:
- closing force of the pressured gas on the cupseal
- striking mechanism, sealing and cocking
There is simply no way how go around these problems... because the mechanism is in-line, all goes in the same way and there are simply such like problems.
When you can not defeat them, you need ally with them. Because you have problems with the pressured gas, it is better use him to own advantage. Because there are problems with hammer, best solution is make the construction hammerless.
And that leads us to my great Stock Class invention: high-efficient Mule valve system
(I call i so, because it is dumb like mule, but likewise so strong and tough)
There is no hammer, the mechanism is self-cocking. Shooter operation is limited only on reloading of the balls in chamber (I think that there will be moving barrel like in Splatmaster paintgun or in Chaunchat machine gun - the barrel is here simply the lightest an simpliest part, so why do not move with barrel instead of bolt...).
How it works:
1. on beginning dump chamber is empty.
1. pressured gas goes trought the center part of the valve in the dump chamber. Because there is only small hole to outer diameter, the gas has time to push the valve sleeve in only one possible direction - in front and so close the space in chamber.
2. the trigger sear on the diameter lockes the sleeve when he is in front position, where is the chamber sealed.
3. with raising pressure in the dump chamber, the ballance of the forces changes - the gas pushes the sleve trought bigger surface to backward.
4. when shooter fires the gun, the trigger sear is released, valve sleeve is released and accelerated with full power of the gas backward.
5. the whole outer diameter of the chamber opens, the gas is released with maximall speed to chamber - there is no other marker with such like gasflow
6. the pressured gas in the dump chamber is depleted. Begins the 1. phase.
It should work, and it should have no oponents in efficiency. The only question are the exact dimensions, especially of the dump chamber.
The pressure input can be controled by reg and by this way the velocity can be controlled..
Eventually, there can be striker - which will be act like part of trigger.
The biggest disadvantage of this design is imho big pressure on the sear. But you can use cylindrical high face sear on whole diameter. It will be possible use the poppet valve to release the sleeve, but I have doubts about gas loss and about speed of release, when there will be small holes and make equally fast poppet valve means make simply other similar valve.
Originally the idea
came from FASOR (Forward Air - Spring Operated Return) mechanism, the only difference was that the construction was opposite - it should be not used to be self-loading, but for fastest possible valve opening and biggest possible airflow. But then I have find that the return spring is here not necessary. The first model should be only experimental gun - muzzle loadet and chamber pressured with manually operated valve. The curent model can be theoretically used like fully functional stock class paintgun.
Work on prototype are unter way.
(Really it is not nelson. I have dried to construct nelson style in-line hi-flow balanced valve design, with striker, but it was simply useless. Imho you will find nothing better than my Mule design. And he can fit in common nelson style marker. Let the nelsons live with thier KISS principe, or make new construction. BTW im working on Tigershark tunning - with larger powertube ID (4,0 vs 4,8mm) there should be better efficiency than in case of my tunned New Hammer... and even the hammer and bolt of Tigershark looks for me suitable for tunning... altrought it can be funny, I will meet WickedKlown2 Grey Ghost efficiency with him)