Super Bolt and Low pressure upgrades
This is only an idea - it is not supported by mathematics or physics only what I know - which is GCSE grade maths and physics.
Seeing as the superbolt is a lot lighter (1/3 or so) than a normal stock bolt - it shouldn't require as much force to get up to the required speed and force. I know the currect A.I.R. and RT valves are capable of being turned down to get more efficiency but they were not designed for this.
Maybe AGD you could re-engineer a valve so that it will work as efficiently as possible with a superbolt giving more shots (which i would love) and possibly a lower pressure (though not that needed it would be nicer to have a less harsh marker, and give me the chance to use higher grade paint).
Feel free to contradict, insult - congratulate or reward.
A very, very long post...
> There's no way the bolt/power tube is
> acting like a regulator. To do that the
> bolt would have to sit close to it
> rearmost position, the only place an
> air-tight fit occurs.
Regulators do not have to be air tight to do their job in a flow through system. All they must do is restrict the flow sufficiently, causing the downstream pressure to drop. This can be demonstrated with a garden hose and a couple of valves. Since the plunger in the center of the Mag's bolt does not completely exit the powertube, the bolt plunger restricts airflow. The amount of restriction is dependent on the location of the plunger relative to the power tube tip. This position is controlled by the strength of the return spring, the diameter of the bolt plunger, and the differential pressure in front of and behind the bolt. Hence, the bolt and return spring act as a regulator. The spring limits the travel of the bolt, which determines how much the airflow through the powertube is restricted.
> In a closed system, the change in
> pressure will only result from change
> in volume, or change in temperature.
Agreed, in the ideal gas case which is what we're assuming.
> The strength of the spring or weight of
> the bolt has no effect on the pressure
> other than some small amount of loss
> due to temperature.
I believe you're likely correct with regards to the bolt weight, but I'm not so sure about your claims regarding the spring. The only way to find out for sure would be to perform a test using different spring strengths.
> Where does the 350 psi go? Well, to
> start with a lot of it goes right where
> Bad Dave said it goes. Expand the
> chamber to include the powertube and
> bolt and the pressure goes way down.
> But its not enough you say? No its not.
> Think about the relationship of the
> bolt, the bolt plunger (not sure if
> that's the right term) and the power
> tube when the bolt is fully extended.
> There is a HUGE air space between the
> power tube and the body, and the air
> flow is open to that space.
The dump chamber in a Mag is around 0.55 cubic inches in volume, as stated in the following thread:
I do not have my Mag in front of me, so I'm working from memory here. The outer diameter of the powertube is approximately 0.5 inches. The tube is approximately 1.5 inches long. The inner diameter of the powertube is approximately 0.25 inches. The interior volume of the tube would therefore be around 0.07 cubic inches.
The bolt consists of a cylindrical volume with a piston in the middle. The piston diameter is approximately 0.25 inches, and it's about 1.5 inches long. The inner diameter of the bolt is around 0.5 inches, and again, is around 1.5 inches long. The total volume inside the bolt (minus the portion occupied by the piston) would therefore be around 0.22 cubic inches.
I don't necessarily agree with your statement that the air can flow out of the powertube and back behind the bolt. It seems to me that the bolt plunger remains in the powertube; thus, the rear of the bolt itself remains around the exterior of the powertube, restricting airflow into the space behind the bolt. However, I'll assume that you're correct for this calculation.
The inner diameter of the Mag's body is around 1 inch. The region between the dump chamber and the bolt's rear face when the bolt is in its forward position is about 1.5 inches long. The total volume of this space (minus the portion occupied by the powertube) would therefore be around 0.88 cubic inches.
0.88 + 0.22 + 0.07 = 1.17 cubic inches.
Including the dump chamber volume brings this up to 1.72 cubic inches, a factor of right around 3 increase in volume. By your argument (and my estimates of sizes), the behind ball pressure would be around 130 psi. We've still got a factor of two somewhere that isn't taken care of yet. Even if we increase the lengths of the powertube, bolt, etc to 2 inches, we're still significantly on the low side in terms of required volume.
> But that STILL isn't where ALL of it
> goes. Who ever said that the pressure
> in the entire chamber/power tube/bolt
> system is evenly distributed. Sure, if
> you leave it long enough it will be,
> but you can rest assured that a
> pressure wave runs down the powertube,
> bounces around as it tries to avoid the
> bolt plunger, and then heads down the
> bolt to find the ball. By the time the
> REST of the air pressure gets there,
> the ball has begun moving down the
> barrel, further enlarging the volume so
> the bulk of the air doesn't seem to
> produce as much pressure at the site of
> the ball.
In the thread whose URL I listed above, Tom posted a picture of an Angel's pressure curve, showing when the ball began its motion relative to the peak pressure in the barrel. He has stated that the ball begins its motion pretty darn close to the top of the pressure curve, regardless of the type of gun being fired.
To reach the total volume (chamber + powertube + bolt + space behind the bolt + volume between bolt and ball somewhere down the barrel) which would drop the pressure down to around 60 psi, the ball would have to be around 5 inches down the barrel. This conflicts with the above paragraph in terms of when the peak pressure occurs.
The only explanation I can come up with is the plunger is restricting the airflow through the powertube, thus limiting the peak pressure. Since the bolt return spring strength is what is limiting bolt travel, we've got a regulator of sorts.
> Bjjb99....just out of curiosity, you
> say the valve would need to be
> increased by a factor of 6x. If that is
> the case, than how do some of these lp
> guns do it without having a dump
> chamber the size of pop can?
An interesting question... here's my take on it. Many lp guns operate at a lower chamber pressure than the Mag (250 psi versus the Mag's 400 or so). Tom has stated that the Mag has one of the lowest behind-ball pressures in the paintgun world. His plot of the Angel's pressure curve shows a peak behind-ball pressure of around 100 psi for that gun. If you start with 250 psi and only drop to 100, you don't need nearly as large a volume increase as you would going from 400 psi down to 60. Thus, the lp guns that start with a lower operating pressure have no need for soda can sized volumes into which the pressure can expand. Athomas has already stated that initial chamber sizes in lp guns can be 4 times that of a Mag.
> Another thing that is apparent on the
> mag is that when chamber volume
> doubles, the operating pressure is NOT
> cut in half. It will go down, but is
> not a 50/50 relationship.
I'm pretty sure I disagree with this statement. Can you point me to a reference which explains what you're saying? Maybe it's the way it's worded, but it sounds like you're darn close to violating a thermodynamic law or two.
> The mag operates at about 60 psi max in
> the barrel as the ball is fired. This
> is achieved as the 400 psi is forced
> through a smaller ventrical called the
> power tube. This acts as a restrictor.
> As the air exits the other end of the
> tube into the barrel it pushes the ball
> forward causing the barrel volume to
> increase. Due to the increasing volume
> and the restricted flow, the pressure
> never gets above 60.
That's a good concise description of the Mag's behavior. The only thing I might add is that the bolt plunger does not completely exit the powertube, further restricting the airflow.