wrote: I'm not sure that the Renolds #
is applicable to a Gas [Air] only applies to Fluids for determining whether
you have Laminar or Turbulant Flow for Thermodynamic Calculations. Surely
once you have a Vacuum the Pipe/Tube is empty so you are Sucking Nothing
other than any Air that Leaks in? Therefore Pipe Size/System
Volume is probably best kept to a minimum?
^^^^^^^^^^^^^^^^
I usually edit a post down to the "bare bones" that I want to comment on.
However, I have to quarrel with most of what you say. Reynolds Number
applies to "fluids." Air is a fluid. It has to do with calculating the
pressure drop in fluid flow, in both laminar and turbulent flow, and in
estimating when the transition from laminar to turbulent takes place.

In a practical vacuum system the pipe is NOT empty. There is a pressure
gradient in the pipe from the chuck all the way to the pump suction. This
gradient is what causes the air to flow toward the pump. Making the pipe
smaller increases the flow resistance, and reduces the capacity of the pump
to cope with leaks. In any practical system, the volume in the pipe will be
quite small compared to the capacity of the pump. The extra volume you add
by making the pipe large will delay the pull-down by a second or two,
perhaps. But, making the pipe too small could result in so much pressure
gradient that the pressure inside of the bowl will rise and interfere with
the holding power of the chuck.

Incidentally, though it has not been mentioned, for the same reason that the
pipe should be large, it should also be short.