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Unread 20-01-2012, 09:31
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Re: pneumatics or motors?

OK. Lets go through this:

Quote:
Originally Posted by DavisDad View Post
The 10 CFM fills an accumulator (reservoir) until charged to about 2-3 PSI.
1: How do you charge the accumulator without using a valve(0.32CV) between the accumulator and the cannon?

Quote:
Originally Posted by DavisDad View Post
The compressed air is released directly into the end of the cannon; like a potato cannon. The air is released very fast and the 2 psi acts against the 50 sq.in. surface of the ball = 100 lb force at initial release.
2: In order to release the air that fast you would need either a vane valve or sprinkler valve. Both have CVs too high for FIRST.
3: Consider your mass flow. As the valve is opened the air starts to flow and pressure begins to build in the cannon (I'll ignore leakage around the ball, which you'd want to lower frictional forces). When the pressure gets to ~0.15PSI (12 oz acting on an 11 oz ball) the ball will start to move up the cannon.

Quote:
Originally Posted by DavisDad View Post
My calcs say I need about 15 ft-lb energy to accelerate the ball to about 31 ft/sec. The size of the accumulator will determine the final exit pressure on the ball. Of course leakage around the ball is a big variable.
4: Pressure will remain ~ 0.15PSI as the air fills the, now additional, volume created by the ball movement. giving you only .75LBf of the 15LBf that you need.

My guess is that the ball never leaves the cannon, as the leakage around the ball will probably have a higher CV than the CV of the valve used.
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