Bungy and Surgical tubing

[Mike Betts]

Originally Posted by boomergeek

Does your piston move during the shot? Most video examples I've seen of various pneumatic/tubing kickers show the piston moving during the shot.
If your piston moves during the shot, does it move faster than 20 inches per second?

Has Bimba (or any other actuator expert) sanctioned any conditions where a piston is "engineered appropriately" to move the piston faster than 20 inches per second?

Dick,

This "specification" has been floating around these boards for a while now.

I'd love to find out the exact source of the 20"/sec specification. I downloaded the Bimba manual and can find it nowhere.

I calculate a 1" bore cylinder will move at about 70" per second (unloaded, 45 PSI delta with about a 2 CFPM airflow).

This was brought up in another thread. Upon reflection, my thoughts are:

1. If the cylinder is rated at 125 PSI, I would think it should be built to survive a 110 PSI delta actuation over years of use.
2. The rules state no more than 60 PSI as a working pressure.
3. Assuming that the piston is used to deflect the spring assist at a 45 PSI delta, then the effective contribution of the spring is that of a 45 PSI delta.
4. Added to the 45 PSI delta of the pneumatic system, you have an effective force of 90 PSI delta acting on the piston.

Even with pre-charged cylinders at some percentage extension to maximize speed and direct exhaust at .3 cv, I'm having a difficult time getting a dangerous material fatigue scenario for an expected lifetime of a couple of hundred two minute matches.

Like I said, I'd love to get to the source...

Regards,

Mike