I'm getting different result from what you got using the first equation that I had presented in the original post.
T = (V / D) * loge (A / (A - B))
V = 0.03472 cu. ft.
D = 0.42 scfm
gives me
T = 0.133 min which in seconds comes to
T = 8 sec
+/- 50 mbar would do.
Yes I agree with you that the equations don't take into account the pipe dimensions and the valve. However I needed a rough estimate for pump sizing.
I am getting conflicting results on finding the pump downtime for a diaphragm vacuum pump for air.
There is a 60 cu. inch vessel that I need to evacuate to 600 mbar abs. in about a second.
The current pump that I have has the following ratings
Free flow = 12 liter/min
Max vacuum = 500 mbar...
