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Originally Posted by DavisDad
I'm guilty... 
I couldn't let go of the idea. I had to know how the leakage around the ball would affect the performance.
I rigged up an Extrol tank (hydronic expansion tank) to a short length of Sonotube (big toilet paper tube). The ball is fairly tight with less than 1/16 gap = (tube ID - ball OD)/2. I had my son hold down the rig and I jammed a baseball bat in from the back to get a good force on the diaphragm. The ball went about 10'; OK but not great. A SWAG of the leakage is about 1/2 the volume pushed by the diaphragm leaks by the ball.
There is also an affect I've observed from testing with a reversed shop vac: - I had the hose stuck into a bucket that fit on the OD of the Sonotube
- Before I put stops at the bottom of the Sonotube, I tried the rig letting the ball fall into the bucket where gap was large
- When I turned on the vac, the ball was held in the bucket = the rig sucked the ball back
Maybe there is some back pressure from the leaking air creating high pressure in front of ball (drag).
Extrol sketch --> http://www.arttec.net/Solar/12-24-10...gm_diagram.jpg
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By using a rubber diaphram, you are basically creating your own compressor (without the bellows valve, and using the ball as a poppit valve).
As such you may run into issues with <R69> and proving <R73>
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[R69] All pneumatic components must be COTS pneumatic devices rated by their manufacturers for working pressure of at least 125psi (with the exception of [R71]-D).
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[R73] Compressed air on the Robot must be provided by one and only one compressor. Compressor specifications may not exceed nominal 12V, 1.05 cfm flow rate, 120 psi maximum working pressure. Off-board compressors must be controlled and powered by the Robot.
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I'd suggest you Q&A this before you bring it to competition.