Mon Dec 11, 2017 1:08 pm
The length would play a role, but a relatively minor role (in this relatively short length of hose). The length can make a difference, but it is not as critical as the diameter.
The new EPDM hoses that Bryan is offering are actually longer than the silicone hoses and I have not noticed any resistance difference (and haven’t heard anyone else make a comment). There may be a measurable difference if we took some precise instrumented measurements under very controlled conditions, but none of the divers have noticed a difference.
As I mentioned, the cross-sectional flow area is a function of the square of the diameter.
The area of a circle = diameter square x Pi/4 (Also expressed as the radius square times Pi).
A = (D^2)* (Pi/4)
or A = (r^2) * Pi
Therefore a small reduction in the hose diameter can make a big difference.
From my observation (and limited testing), the typical one inch diameter is about the optimal minimum diameter for a decent DH with a decent venturi assist. Going smaller can quickly increase the noticeable flow resistance and going bigger can help a bit, but the point of diminishing return is quickly reached.
Due to the area being a square function of the diameter, a small change can make a big difference in either direction.
Note: the inside roughness of a hose (or pipe) will also make a difference. Actually, the roughness can combine with the length to play a significant part in flow resistance, but the diameter is still more critical (especially in this short length of hose/ tubing).
Both questions about the diameter and length of a hose are very good question and I am the subject was brought up. They are both factors in fluid dynamics and my answers come are based on calculations/analysis, observations, and testing. But these are relative statements based on these flow systems, do not assume that they directly apply to other piping or fluid systems.
Luis
Buceador con escafandra autónoma clásica.