Low pressure dump chambers and efficiency

[pbjosh]

Redkey-

I am with my wifey this weekend, she had an Ectopic Pregnancy, and ruptured her falopian tube while I was at Vegas. So I have relocated to my house with everything to help her heal from surgery.

Maybe next time, I have some ACE Racers built that just ROCK and I want to show them off!

Josh

[Redkey]

ugh! Man that sucks.

I hope she gets better soon.

[pbjosh]

So how was STP, I heard it went very well.

Josh

[Redkey]

Ended up staying at home and working.

A bit more productive. Not quite as fun.

How is your wife doing?

[Vegeta]

Originally posted by AGD:
Maybe one way to describe it is like this. If you had a basket of corn kernels pour out on your head you would be annoyed but ok. If you tried to stick your head into a basket of corn it would be a tough task.

OK we have hit a low point! corn kernels? (whistles.....)

OK so big paths w/ corners = little diffrence.
Small paths w/ corners = diffrence. We also have to think about cycle time along with velocity here folks. The more turns the air has to take from valve to ball may not make a big diffrence when firing slow. Take it this way.

Lets say we haev a seupt where there is two turns hte air has to make from the valve to the ball. Now it takes say 15 seconds for the air to get from point A to the ball, going around the corners. Now if hte gun starts to shoot faster, that air will have to be moving thru there to keep up with the bolt, or else the golt will be hitting the ball, and startign to return before the air has completely exited the bolt, and therefore cuaseing the seal between barrel/botl to break and the left air to leak up the feed tube and bobble your balls. The FASTER the air can get out hte bolt, the better, especially durign high feeding rates.

Am I on track here? I have nothing to expiriment or see this on.. just going out on a limb.

Josh is having a heated discussion here, and I am right now behind his story.
He is a damn good designer, and I have seen his new gun, I belive he calls the 'Shiva' project am I right?
Josh im sure we'd love to see some more details on that thing.. maybe it would help in this discussion?

[pbjosh]

Vegeta-

The 'Shiva' was mostly a test mule. I haven't been able to kill the blow-back, and have tabled it for a bit. Sorry. But what I did do is prove my hypothosis that a LP dump chamber gun doesn't need to be in-effecient. So I am happy for a while. And that was with a Dye Boomstick boys, not some long barrel. In fact I needed much more energy to shove a ball out of a 14 j&j than a dye boomer. 240 in*lbs per shot on the 14" compared to 175 in*lbs on the Boomer. Eat that one up you doubters.

As for internal speeds in paintball guns, most of the air is gone in 3-8 milliseconds, ask AGD, he knows. In 1-2 ms the air is at the ball and moving it for the most part.

Josh

[Vegeta]

Hmm.. ok i dont relly know about the times it takes for things to move/flow andall.. I wish I did. 1-2ms wont hurt anything.

[echoes]

One thing to keep in mind is that a dump chamber may be more susceptible to a change in pressure than a poppet valve would be. For example, if you fire your cocker at a high ROF and pressure to the valve drops, dwell will increase slightly helping to compensate. But I can't think of anything like that on the mag or any dump chamber design.

By the way, to whoever it was that said that they didn't think the novas are fast; they are very fast. I've heard that they can even cycle faster than RTs. I don't have any numbers to back that up, but I've owned two novas and it seems possible.

[pbjosh]

One thing to think about with dwell compared to pressure in a poppet is that all the parts have to be balanced, so, if you are not feeding the poppet enough air the valve can open a bit longer and cause a more air to release. That is part of the reason you are suppose to tune your 'cocker to the 'sweet spot'. If you tune over the sweet spot, and then out shoot the reg, then you can shoot hot.

As for the Nova, I am fairly sure it wasn't just a dump chamber design. I took a good look at it, and I think It really shoots from a Poppet Valve Emulator (PVE) style. The Piston would go forward as the reg recharged and before all the pressure would leave the Chamber. Part of the reason for the large port in the front I think might have to do with back pressure on the piston, from the ball as it exited, helps hold the piston open.

If somebody wants to send me a Nova ET I can set it up with a Morlock and Warp, and we could see how fast it really will go!

[ES13Raven]

Originally posted by pbjosh
If you tune over the sweet spot, and then out shoot the reg, then you can shoot hot.

Can you further explain that to me?

[pbjosh]

The 'Sweet Spot'

Oh boy, I will keep this decent and on topic :)

I am not to good at describing these things sometimes. The sweet spot is a point of balance in the valve of a 'cocker or similar gun that the most air flow can run through the gun. It is a balance between the air pressure behind the cup seal and the spring as it acts against the force of the hammer. As you increase pressure into the gun (again, 'Cocker types) you will see the velocity rise, until it gets to a point, then it starts to decrease, and then after a bit more pressure is added, the velocity starts to rise again. The first point that the velocity rises, right at its peak, is the sweet spot. Tuning the gun to a point above that (higher pressure than the sweet spot) allows you to have the velocity increase as you fire at a rate above what your regulator can supply, so you end up with less pressure, making your gun run in the sweet spot, hence shooting higher at times. I hope this answered your question.

Josh

[ES13Raven]

I understand the sweet spot being the point of highest flow and balance between spring tension and pressure.... acts like a bell curve with velocity.

What I don't understand is if you run a higher pressure than the sweet spot, how you could "fire at a rate above what your regulator can supply"?

Wouldn't a higher pressure recharge the valve chamber quicker using the same reg?

[Vegeta]

"The Sweet Spot" - Great explanation.

There are just so many variables here.. whoo!
And just think if people were to be able to tune the spring inside the valve (blowback-type) with a screw on the outside of hte gun just like you would to turn up velocity. More spring bound = diffrent sweet spot.it would peak before the bolthits the all the way mark. Also would result in shorter dwell? Hmmm this takes some thinking. less bound/more rebound of hte spring equals longer dwell time? possible bottom out? more volume? And what if this was implemented on a cocker type valve?

[pbjosh]

ES13Raven-

Quite a few regs just are not that good. Look at AGD's testing of the Govnair, 20 seconds to fully recharge. I had similar issues with a Stab at 180 psi. It took a while to recharge. You could take a Govnair, run it at 300 psi, but have the valve tuned for sweet spotting at 260. Then at high rates of fire, you wouldn't supplying the gun with a full 300 psi. Funny how that works, eh?

Vegeta-

There used to be that adjustment on the Spyder. You could adjust your front screw in or out to adjust valve spring pressure, and the original ones also had a screw on the body where the valve dumped into the bolt to act as a choke to adjust velocity.

Also several other guns had that also, including an adjustment for the F1's (aftermarket) and a couple others. The Original 'Blade' (heavy F1 clone) also came with one. We had one of those. We played around with the front screw alot to figure out how the balance of it all was. Kinda of a cool design in some ways.

I have a CADed cocker body with an adjuster in the front for the valve. It would be involved, but could be done.

Josh

[Vegeta]

I dont know about this WDP reg, but Tom and a guy did soem 'informal' reg testing one time, and posted the results here in deep blue. They tested an RT against an Angel reg i belive. All I can remeber abot it was that the angel's reg (Angel AIR it was?) recharged much slower than the RT.