Finding the Vex Pneumatic System Cv

Vex finally posted component Cv specs. A few were not available from SMC web site but I took a guess at them and approximated the system Cv as follows:
Comments: 1/Cv_sys^2 = sum(1/Cv_i^2) where Cv_i are component Cv’s
4-Jan-10
System Cv Calculation (test config)
Part……..Number,.. n…. Cv……. n/Cv^2
Pressure reg………..1   0.111     81.0… no spec
Reservoir Fitting….1   0.311      10.3… no spec
tire pump fitting…. 1   0.083     144…. no spec
T fitting………………..2   0.356       15.8
Solenoid………………1    0.050     400.0
Valve fitting………….3   0.078     495.9
Cyl fitting……………..1   0.150       44.4
Tubing………………….1   0.110        50.4… assumes .11 Cv per meter
…………………….. ……………….sum 1241.895
…………………….. ……………….Cv_sys 0.028

So the Cv_sys of .028 gets closer to the .015 that I need to match the test results. The valve fitting and the Solenoid dominate. I would have thought the tubing would have contributed more. (I assumed a meter length for the calculation).

I suspect there are a few more contributers to system pressure losses that need to be added in somewhere. I couldn’t find anything in the cylinder spec re flow coefficients but I’ll bet there are some pressure losses across the cylinder input manifold.

I measured the Coulomb friction losses at about 2 oz which should be negligible.

So, I’m still stuck with a .5 fudge factor but that feels a little better than having a .3 factor

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