AGD
04-27-2002, 01:11 AM
Guys,
You are making sense in your arguments but are working with limited data. You will have to take my word on the stuff I will tell you because unless you came here and go through the testing I can't verify the results.
We first setup our gun dyno in the late 80's because the Sheridan Pump guns got way less efficiency than the Nelson based guns. Sheridans got about HALF the number of shots from a 12 gram. We cut a deal with PMI that they would pay us a big sum of money for every extra shot we got out of their guns. We were very motivated to make them more efficient.
We started into the project with the same thoughts you have here, that it's all about flow. Make the flow better you get better efficiency. This made sense because the Nelson had a straight though power tube and the Sheridan had all kinds of turns and chambers.
We spent month after month systematically working though the passages, making them bigger and smaller, smoothed all the curves etc. At each step we used the dyno to record the data. After all the flow path work, the data showed no significant difference in efficiency.
Confused we targeted the poppet valve itself. We had good knowledge of valve systems in car engines and theorized that a "3 angle valve job" that helped car performance would also help the poppet valve. We were convinced that the poppet had the highest air flow and thus would be most effected by flow improvement. After making many of the most perfect, miniature, 3 angle poppet valves you ever saw, we were still at the same efficiency.
Because it was the last thing, we now focused on the hammer itself and started changing weights and springs. Surprisingly we finally did see a change in efficiency. This did not jive with our theory on air flow. In one experiment we drilled a hole in the side of the gun (see, been doing it for years :) and used a pin to catch the hammer as it bounced off the poppet valve. To our amazement the efficiency skyrocketed and matched the Nelson guns.
We now sat down and examined the 6 months of work to see where we went wrong and try to understand what was really happening. We examined all of our pressure behind the ball curves and discovered that no matter how high the pressure peak was, the area UNDER the curve that represented the total energy, was nearly the same. We concluded that you had high variability in how hard you "hit" the ball as long as you didn't run out of barrel length to accelerate it. This is in direct conflict with the better flow theory.
We also looked at the pressure build up times. This is the time it takes to go from 0 to peak pressure. Again to our surprise, the time as about the same no matter how high the pressure peak was.
After all this we came to some conclusions which have remained true for a decade.
1. the efficiency problem in the Sheridan was caused by the bolt bouncing off the poppet valve and hitting it several more times before it came to rest. Each hit was AFTER the ball left the barrel and just released air needlessly. Lighter bolts reduced the problem. The data showed the bouncing bolt for the whole 6 months but we just ignored it as noise. Lesson learned, do not make assumptions based on what you think you know, look at ALL the data.
2. It takes X amount of energy to accelerate a paintball to 300 fps, no more no less. For years later we always laughed when everyone got excited about claims of a new gun with double the efficiency. Lesson learned, within a range it doesn't much matter if its lower or higher pressure you get the same efficiency.
3. Inertia plays a key role in the paintball acceleration. We feel that inertia holds the paintball in place while the pressure builds up behind it, thus giving a relatively stable build up time. The pressure build up is now causing the pressure to come toward equilibrium between the poppet valve and the back of the ball and this REDUCES flow rates. Because the entire chamber behind the ball is being pressurized, flow is not a critical factor WITHIN A RANGE. This is not to say if you made the flow paths 1/16th of an inch it wouldn't effect anything. I am saying that with reasonable size flow paths curving each 90 degree bend has very little effect.
My research conclusions are that most flow paths have little to do with efficiency. The point many of you are touching but not going into enough depth on is the reciprocation of the bolt system. Yes as you concluded reciprocation of the bolt takes energy, what you have not considered is that how FAST you move the bolt will determine HOW MUCH energy. The Mag with a superbolt has 18 FPS bolt speed, the Cocker has 4 FPS. See if you can get the Cockers bolt up to 18 FPS and see where your efficiency goes. Bob Long told me if he ups his ram pressure to 100 psi his efficiency goes to hell, wonder why... If you think about it, if flow did make a difference then the shortest path would have the most advantage. Between the Cocker and the Mag there is a whole lot of difference in what the air has to travel through.
Submitted for your enjoyment,
AGD
You are making sense in your arguments but are working with limited data. You will have to take my word on the stuff I will tell you because unless you came here and go through the testing I can't verify the results.
We first setup our gun dyno in the late 80's because the Sheridan Pump guns got way less efficiency than the Nelson based guns. Sheridans got about HALF the number of shots from a 12 gram. We cut a deal with PMI that they would pay us a big sum of money for every extra shot we got out of their guns. We were very motivated to make them more efficient.
We started into the project with the same thoughts you have here, that it's all about flow. Make the flow better you get better efficiency. This made sense because the Nelson had a straight though power tube and the Sheridan had all kinds of turns and chambers.
We spent month after month systematically working though the passages, making them bigger and smaller, smoothed all the curves etc. At each step we used the dyno to record the data. After all the flow path work, the data showed no significant difference in efficiency.
Confused we targeted the poppet valve itself. We had good knowledge of valve systems in car engines and theorized that a "3 angle valve job" that helped car performance would also help the poppet valve. We were convinced that the poppet had the highest air flow and thus would be most effected by flow improvement. After making many of the most perfect, miniature, 3 angle poppet valves you ever saw, we were still at the same efficiency.
Because it was the last thing, we now focused on the hammer itself and started changing weights and springs. Surprisingly we finally did see a change in efficiency. This did not jive with our theory on air flow. In one experiment we drilled a hole in the side of the gun (see, been doing it for years :) and used a pin to catch the hammer as it bounced off the poppet valve. To our amazement the efficiency skyrocketed and matched the Nelson guns.
We now sat down and examined the 6 months of work to see where we went wrong and try to understand what was really happening. We examined all of our pressure behind the ball curves and discovered that no matter how high the pressure peak was, the area UNDER the curve that represented the total energy, was nearly the same. We concluded that you had high variability in how hard you "hit" the ball as long as you didn't run out of barrel length to accelerate it. This is in direct conflict with the better flow theory.
We also looked at the pressure build up times. This is the time it takes to go from 0 to peak pressure. Again to our surprise, the time as about the same no matter how high the pressure peak was.
After all this we came to some conclusions which have remained true for a decade.
1. the efficiency problem in the Sheridan was caused by the bolt bouncing off the poppet valve and hitting it several more times before it came to rest. Each hit was AFTER the ball left the barrel and just released air needlessly. Lighter bolts reduced the problem. The data showed the bouncing bolt for the whole 6 months but we just ignored it as noise. Lesson learned, do not make assumptions based on what you think you know, look at ALL the data.
2. It takes X amount of energy to accelerate a paintball to 300 fps, no more no less. For years later we always laughed when everyone got excited about claims of a new gun with double the efficiency. Lesson learned, within a range it doesn't much matter if its lower or higher pressure you get the same efficiency.
3. Inertia plays a key role in the paintball acceleration. We feel that inertia holds the paintball in place while the pressure builds up behind it, thus giving a relatively stable build up time. The pressure build up is now causing the pressure to come toward equilibrium between the poppet valve and the back of the ball and this REDUCES flow rates. Because the entire chamber behind the ball is being pressurized, flow is not a critical factor WITHIN A RANGE. This is not to say if you made the flow paths 1/16th of an inch it wouldn't effect anything. I am saying that with reasonable size flow paths curving each 90 degree bend has very little effect.
My research conclusions are that most flow paths have little to do with efficiency. The point many of you are touching but not going into enough depth on is the reciprocation of the bolt system. Yes as you concluded reciprocation of the bolt takes energy, what you have not considered is that how FAST you move the bolt will determine HOW MUCH energy. The Mag with a superbolt has 18 FPS bolt speed, the Cocker has 4 FPS. See if you can get the Cockers bolt up to 18 FPS and see where your efficiency goes. Bob Long told me if he ups his ram pressure to 100 psi his efficiency goes to hell, wonder why... If you think about it, if flow did make a difference then the shortest path would have the most advantage. Between the Cocker and the Mag there is a whole lot of difference in what the air has to travel through.
Submitted for your enjoyment,
AGD