Pressure-flow characteristic for a 4-Way Directional Valve
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I've to parametrize the block "4-Way Directional Valve" in Simscape Fluids by using Pressure-flow characteristic. I've read carefully the documentation: https://it.mathworks.com/help/physmod/hydro/ref/4waydirectionalvalve.html, but unfortunately not everything is clear. In particular the pressure differential vector is not well defined (what positive pressure or negative pressure means?) and the same for the volumetric flow. Assuming positive pressure drop from A to P and positive flow from P to A I've used the following parameter, but I'm note sure it's right, someone could confirm?
x= [0,2,4,6,8,10]; %mm, spool position
P=[5,50,315]; %pressure vector bar
q5b= [0,0, 4, 14,31,58]; %liters/minute at 5 bar
q50b=[0,0, 8, 20,35,58]; %liters/minute at 50 bar
q315b=[0,0, 13, 23,33,40]; %liters/minute at 315 bar
M=[q5b' q50b' q315b']; %volumetric flow rate table
Yifeng Tang on 20 Jul 2022
I believe the pressure differentials refer to p.P-p.A, p.P-p.B, p.A-p.T, p.B-p.T. The flow direction is defined in the save way.
Your parameters look OK, although I suspect you may run into issues if for example, somehow p.A is higher than p.P. The extrapolation may give you unexpected results.
Also, consider use isothermal liquid (IL) domain instead of hydraulics: https://www.mathworks.com/help/physmod/simscape/ug/upgrading-hydraulic-models-to-use-isothermal-liquid-blocks.html