Unit of Hydraulic Resistance

It doesn't have a named unit. You could define it by analogy with electric current flow, but you would need to calculate pressure drop first, so it wouldn't be any help.

Also electricity obeys Ohm's law (for ordinary conductors) and current varies directly with voltage. For fluid flow, in most practical cases ΔP varies as Q².

Valves, specially flow control valves, are often described by Kv (analogous to conductance, reciprocal of resistance), defined by

Kv = Q*√(SG/ΔP) where Q is flow in m³/h, SG is fluid specific gravity and ΔP is pressure drop in bar. (there's also Cv which is similar but in American units)

Cheers.......Codey

friction.

Pressure drop per unit length of pipe.

The Weisbach-Darcy equation can be used to work it out from first principles in the case of non-compressible fluids.

The electrical equivalent is voltage drop per unit length of conductor.

Electrical resistance (ohm) is voltage drop per amp. You can divide by length of conductor if you want ohm per unit length.

And if by analogy hydraulic resistance is defined as say bar/(m³/h) there could be a problem as usually ΔP varies as Q².

Also there's no problem using the Weisbach-Darcy equation for compressible fluids. Pressure and temperature have to be handled correctly, but then it's OK.

Cheers........Codey

To be consistent with the ISO units it should be N*m^-2/(m^3*s-1)=N*s/m^5.

A specific resistance would be related to the tube length but a global resistance has not to be bound to the length. The Ohm is a global unit so that for similitude the hydraulic unit has as well to be global.

Years ago an American company supplier of miniature hydraulic resistor -Lee- used the "LOhm" which could be either read as Lee-Ohm or as Liquid-Ohm.