The "90psi" graph...

[SLICEnDICE]

Transducers

I see clearly now and understand.

[Kweasi]

I'm still not clear here....

It's my understanding that the "90psi" and hense the 32lbs force figures are the "threshold" before the ball starts to move. That is to say the ball remains stationary untill the pressure behind it reaches the threshold and overcomes the forces holding the ball still.

But this does not compute- if that were the case than how can a bolt supplying only 8lbs force (ie Matrix) chamber a ball?

-Kweasi

[Doc Nickel]

Kwayze- keep in mind that, in the millisecond-times we're looking at here, it's also a matter of "that's how much pressure managed to reach the breech before the ball's friction and inertia were overcome and it began to move."

In other words, the chamber- the breech and space behind the ball- was filling faster than the ball could 'react'.

Liken it with a golf ball being hit: The ball actually compresses a little and deforms, THEN starts to accellerate off the tee.

I'm not saying the paintball deforms, I'm saying that the force builds up before the ball begins to move- and the faster the force builds, the higher the apparent pressure before that movement.

So it's not so much that it takes X pressure to get the ball going, its a matter of that's how fast that particular marker, at that pressure, with that valve dwell time and that particular valve and bolt, can pressurize the breech, and to what level, before the ball's intertia is overcome and begins to accellerate.

I'd be interested to see those same transducers in Nova, which is supposed to operate normally at 90 psi- I'd wager the breech pressure before the ball moves is far lower, but the "peak" as depicted above is spread out over a far longer time.

Doc.

[sniper1rfa]

im with doc, also, there is the sticktion (is that actually a word?) before the ball unseats itself.

[Kweasi]

AH HA! That clears it up a good deal. Much thanks.

But...
If different valve set-ups do in fact cause different relationships between peak-pressure and ball movement, does that suggest that "low-pressure" markers *really are* gentler on paint?

-Kweasi

[sniper1rfa]

technically, yes, but you wont notice it, as there is no way in hell that 90 psi will break a ball (or come remotely close) with only a little friction and its own inertia opposing its movement.

[athomas]

The pressure in the chamber is about 350psi. When the bolt moves forward it releases the pressure behind the ball. When the pressure behind the ball is greater than the friction and stationary inertia forces on the ball, the ball begins to move. The rate of acceleration of the ball is directly proportional to the pressure exerted behind it.

Edit: This explaination is for a mag valve.

So, as air/gas builds up pressure behind the ball, it starts moving. Initially, the rate of pressure increase is greater than the rate of speed increase. Then as the speed increases due to acceleration, the area behind the ball increases faster than the chamber can pressurize it. Even though there is 350psi in the chamber, the pressure never gets above 60psi behind the ball. This is where the pressure graph shows a decline in overall pressure behind the ball. At some reduced pressure, the forces behind the ball will not equal the frictional forces in front and along the sides of the ball. The ball will start slowing down.

This happens very fast. To be able to measure it with a degree of accuracy takes precise instruments. The data is collected electronically and is subject to calibration/offset, but relationship to high and low is always constant. You just have to know where zero is and calibrate the data accordingly.

[Kweasi]

Offsetting that graph to "zero" it, effectively moves the whole thing up 5 units. That would mean the actual "theshold pressure" is 95psi, would it not?

-Kweasi

[athomas]

I agree. The corrected data may have to be moved up 5psi. That would mean the actual psi behind the ball is 95psi.

[Kweasi]

(Musta read my previous post before I edited it and corrected my error- just clarifying).

-Kweasi